Download Nutritional Aspects of Inborn Errors of Metabolism

Feeding the Sick Infant, edited by Léo Stem.
Nestlé Nutrition Workshop Séries, Vol. 11.
Nestec Ltd, Vevey/Raven Press, New York
© 1987.
Nutritional Aspects of Inborn Errors
of Metabolism
Michel Vidailhet
Department of Pediatrics 3, Hôpital d'Enfants, 54511 Vandoeuvre-lès-Nancy, France
GENERALITIES
Introduction
Inherited metabolic disorders in volve différent nutritional aspects. On the one
hand, the disease itself can impair normal nutrition. During the end of the fetal
growth period and the first two years of life, the human brain grows at an impressive rate. This brain growth spurt period (1) is associated with a very high rate of
protein synthesis that makes the central nervous system vulnérable to any interférence with protein synthesis. Biochemical insuit at this critical period may hâve a
permanent effect on brain function.
The accumulation of one or more substrates above an enzymatic block can affect normal metabolism and nutrition. For example, in amino acid disorders the
high tissue levels of accumulated amino acid may competitively inhibit the transport of other amino acids sharing the same transport mechanism. Amino acids in
excess may interfère with the activity of enzymes involved in the metabolism of
other amino acids. Short-chain fatty acids, oxo-acids, and other organic acids interact with ureogenesis, gluconeogenesis, pyruvate metabolism, etc. In fructose intolérance, the accumulation of fructose-1-phosphate causes the trapping of inorganic phosphate. The fall in cellular ATP and ADP inhibits several enzymatic
activities and results in altérations of energy metabolism.
On the other hand, the metabolic block can induce severe deficiencies in one or
more metabolites normally produced by the pathway. In ail urea cycle disorders,
except arginase deficiency, arginine becomes essential; without arginine supplementation, stunted growth and hyperammonemia occur despite protein restriction.
Undemutrition may be the conséquence of gênerai metabolic disturbances.
Chrome hypoglycemia, lactic acidosis, and secondary hypercorticism explain the
poor growth observed in glycogenosis type I. Severe and progressive impairments
of liver function and, to a lesser degree, of rénal tubular function play a major
rôle in the development of malnutrition, which appears in galactosemia, fructose
intolérance, or in hereditary tyrosinosis.
205
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INBORN ERRORS OF METABOUSM
Even in lysosomal disorders, stunted growth can begin in the first few weeks of
life, as in Wolman disease, probably because of the importance of the liver and
small bowel lésions in this disease.
In transport mechanism disorders, levels of spécifie nutrients may be decreased,
with, as a conséquence, symptoms of deficiency, as in acrodermatitis enteropathica secondary to zinc malabsorption.
On the other hand, surprisingly enough, cystinuria-lysinuria does not resuit in
lysine or arginine deficiency, despite the increased rénal excrétion and the intestinal malabsorption of thèse amino acids. Such an apparent contradiction is now well
explained by the importance of direct intestinal absorption of di- and tripeptides.
Dietetic Treatment
Because of the multiplicity of inborn errors of metabolism, it is not possible
to review ail their nutritional drawbacks. Some metabolic disorders are harmless
variations of normal metabolism (e.g., essential fructosuria, cystathioninuria),
whereas others cause severe illness or mental détérioration early in life. The latter
are often treatable by means of spécial diets and their nutritional aspects appear
most important for clinical practice. A block in galactose, fructose, or amino acid
metabolism leads to accumulation of thèse substrates and their metabolites, which
can be prevented by spécifie restricted diets. Such diets may hâve to be continued
for many years, sometimes indefinitely, as in maple syrup urine disease (MSUD),
urea cycle disorders, galactosemia, etc.
The prolonged use of a synthetic or semisynthetic diet may hâve adverse effects
if the absolute and relative amounts of the différent nutrients are not well provided.
Thèse diets must provide: (a) adéquate calorie intake; (b) minimum requirements
of essential amino acids and nitrogen; (c) vitamins, minerais, and trace éléments
in sufficient amounts; (d) normal products of the metabolic pathway that can no
longer be produced and that hâve essential functions (e.g., tyrosine in phenylketonuria (PKU), arginine in urea cycle disorders, cysteine in homocystinuria, free
glucose in glucose-6-phosphatase deficiency). The biodisposability and intestinal
absorption of several nutrients, such as vitamins or trace éléments, may be very
différent between synthetic diets and normal foodstuffs. Apart from the main effects intended by the treatment, it is important to be concerned about ail nutritional
problems that may resuit from the disease and its dietetic therapy.
According to the type of metabolic disorder one can distinguish several kinds
of dietetic manipulations.
Supplementation
This is the easiest to perform. An example is zinc supplementation for acrodermatitis enteropathica. In Menkes disease parenteral supplementation with copper
gives much less satisfactory results.
A particular group of inherited metabolic diseases is the group of vitamin-
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INBORN ERRORS OF METABOUSM
dépendent disorders. Several amino acidemias and organic acidemias are completely or partially cured by large doses of vitamins that are the precursors of spécifie cofactors involved in defective enzymatic reactions. Table 1 lists thèse diseases. According to the kind of enzymatic deficiency, a metabolic disorder, as
methylmalonic acidemia, may be fully or partially responsive or unresponsive to
B12 vitamin therapy. In every instance it is important to try such cofactor therapy,
which is easier to apply than restricted diets.
Exclusion
Such diets can be proposed when the nutrient to be excluded is not an essential
one. This is the case for galactose (galactosemia, galactokinase deficiency, glycogenosis type I) and for fructose (fructose intolérance, fructose-1, 6-diphosphatase
deficiency, glycogenosis type I).
Restriction
In disorders involving an essential amino acid, the diet must supply the minimal
requirement for this amino acid that is restricted relative to the total protein intake.
Most of the natural protein is replaced by a protein substitute deprived of this
amino acid (Tables 2 and 3).
TABLE 1 . Amino acid and organic
acid disorders
that may be responsive
Disease
to vitamin
therapy
Vitamin
Dose
Homocystinuria (cystathionine synthetase deficiency)
Cystathioninuria
Hyperoxaluria
Xanthurenic aciduria
Pyridoxine
1 0 0 - 1 5 0 mg/day
Methylmalonic acidemia (MMA) (mutase deficiency)
Homocystinuria + M M A + hypomethioninemia
B 12
0.25-1 mg/day
Homocystinuria + hypomethioninemia
Folie acid
1 0 - 5 0 mg/day
Maple syrup urine disease
Lactic acidosis (pyruvate dehydrogenâte [PDH]
deficiency)
Thiamin
1 0 - 2 0 mg/day
Dicarboxylic aciduria
Type 2 glutaric aciduria
Riboflavin
100 mg/day
Hartnup disease
Niacin
5 0 - 2 0 0 mg/day
Hyperphenylalaninemia with dihydropterin synthetase
deficiency
BH„*
3 - 5 mg/kg
Tyrosinemia
C
5 0 - 1 0 0 mg/day
Multiple carboxylase deficiency (3-methylcrotonylglycine,
propionic, lactic acids)
Biotin
10 mg/day
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209
TABLE 3. Low amino acid and galactose-free substitutes
Disorder
Substrate lowered
Name of Product
Cystinosis
Maple syrup urine disease
cystine (0.5 g/100 g)
Branched-chain amino
acids
Homocystinuria (classical
form)
Methionine
Tyrosinosis
Phenylalanine and tyrosine
Histidinemia
Histidine
Hyperlysinemia
Urea cycle disorders
Lysine
Nonessential amino acids
Propionic and
Methylmalonic acidemias
Galactosemia
Nitrogen
Isoleucine, methionine,
threonine, valine
Galactose
Albumaid X Cysf
M.S.U.D. Aid·
Leucidonfc
M.S.U.D. 1 and 2e
Albumaid X Meth*
Methionaid"
Hom 1 and 2e
Albumaid X Tyr*
Tyrosinaid*
Tyrosidon"
Tyr 1 and 2e
Histinaid*
Histidon"
Hist 1 and 2e
Lys 1 and 2e
Essential Amino Acid
Mixture*
U.C.D. 1 and 2e
Ketosteril"
OS 1 and 2e
Galactomin 19*
Nutramigen"
Pregestimil·
Isomil'
Prosobee"
Vegelact9
•Scientific Hospital Supplies (England)
•"Nutricia (The Netherlands)
c
Milupa (Fédéral Republic of Germany)
''Fresenius (Fédéral Republic of Germany)
"Mead-Johnson (United States)
'Ross (United States)
«Gallia (France)
For PKU, see Table 2.
A major danger of such diets is the occurrence of nutritional deficiencies, particularly a deficiency in the restricted amino acid. Phenylalanine deficiency owing to
overtreatment of PKU has been well described. The baby fails to gain weight; develops a severe, red, cutaneous rash starting in the napkin région; vomits; becomes
anorexie and léthargie; and may develop alopecia, edema, and fréquent infections.
Death or définitive mental retardation may ensue. Deficiency of other essential
amino acids has the same gênerai effect.
In several diseases such as MSUD, propionic acidemia (PA), B12 unresponsive
methylmalonic acidemia (MMA), and infantile tyrosinosis, the borderline between
deficiency and excess is narrow, and monitoring is more difficult than in PKU.
Low protein diets, in which total protein is restricted and replaced by nonprotein
calories, are necessary in several diseases such as urea cycle disorders. They give
210
INBORN ERRORS OF METABOUSM
way to protein lack and sometimes necessitate the use of an essential amino acid
mixture or of keto- and hydroxy-analogues of essential amino acids.
Emergency Conditions
Some of the diseases manifest themselves in severe acute forms, particularly in
the neonatal period. This is the case for several amino acid disorders like MSUD,
urea cycle disorders, MMA, PA, and isovaleric acidemia (IVA). Certain clinical
findings are suggestive of a hereditary metabolic disease that frequently mimics
neonatal sepsis. An important négative finding is the absence of fetal or périnatal
distress that might explain the observed abnormalities. Metabolic diseases are
characterized by a silent interval of variable duration (5-6 days in MSUD; 2-4
days in PA, MMA, and IVA; 2-6 hr in severe pyruvate carboxylase deficiency).
It is in the second stage that symptoms occur, at a time when placental élimination
no longer plays its rôle. Several features are characteristic: Thèse include neurological manifestations such as altérations in consciousness (lethargy, altemating
hyperexcitability, and somnolence), hypertonia, convulsions, and feeding problème. Other suggestive findings include vomiting, abnormal breath or urine odor,
a hemorrhagic syndrome, and jaundice. A number of simple laboratory tests can
be diagnostically helpful in newborns thought to hâve a hereditary metabolic disorder. Blood déterminations should include true glucose, electrolytes, acid-base
equilibrium, ketonemia, clotting factors, calcium, transaminases, and amino acid
chromatography. Several simple urinary tests are helpful, including déterminations
of ketones (Acetest), reducing sugars (Clinitest), glucose (Clinistix), and alphaketo-acids (2-4 DNPH test). Depending on the suspected etiology, more specialized testing can be undertaken such as an ion exchange chromatography of amino
acids and gas chromatography/mass spectrometry of urinary organic acids. The etiology of thèse acute conditions is summarized in Table 4.
In such acute conditions resulting from amino acidemias, organic acidemias, or
hyperammonemias, temporary removal of protein from the diet and high energy
intake coming from carbohydrates help to limit accumulation of toxic metabolites.
Peritoneal dialysis and exchange transfusions are frequently necessary to remove
toxic metabolites and/or to correct hyperammonemia or severe metabolic acidosis.
AMINO ACID DISORDERS
PKU
Définition and Generalities
PKU can no longer be defined as a phenylpyruvic oligophrenia, owing to the
success of dietary measures in preventing the appearance of mental deficiency in
this disease. PKU is a hereditary metabolic disorder transmitted as an autosomal
récessive trait, and arises from the permanent inactivity of hepatic phenylalanine
INBORN ERRORS OF METABOUSM
211
TABLE 4. Possible hereditary metabolic disorders causing neonatal neurological distress
With acidosis
MSUD (mild acidosis)
Methylmalonic acidemia
Propionic acidemia
Isovaleric acidemia
β-keto-thiolase deficiency
Pyruvate carboxylase deficiency
Multiple carboxylase deficiency
Type 2 glutaric aciduria
HMG CoA lyase deficiency
Nonketotic C6-C10 dicarboxylic aciduria
Congénital hyperlactacidemias
With hypoglycemia
Methylmalonic acidemia
Propionic acidemia
Pyruvate carboxylase deficiency
Multiple carboxylase deficiency
Types 1 and 2 glutaric aciduria
HMG CoA lyase deficiency
Nonketotic C6-C10 dicarboxylic aciduria
With alkalosis
Urea cycle enzyme disorders
CPS I deficiency
OCT deficiency
Arginosuccinate synthetase deficiency
Arginosuccinase deficiency
Arginase deficiency
With ketosis
MSUD
With ketosis {contd.)
Methylmalonic acidemia
Propionic acidemia
Isovaleric acidemia
β-keto-thiolase deficiency
Pyruvate carboxylase deficiency
Multiple carboxylase deficiency
CoA transferase deficiency
With hyperammonemia
Urea cycle enzyme disorders
CPS I deficiency
OCT deficiency
Arginosuccinate synthetase deficiency
Arginosuccinase deficiency
Arginase deficiency
Organic acidemias
Methylmalonic acidemia
Propionic acidemia
Isovaleric acidemia (+.)
β-keto-thiolase deficiency
Pyruvate carboxylase deficiency
Multiple carboxylase deficiency
Type 2 glutaric aciduria
HMG CoA lyase deficiency
Hyperornithinemia with homocitrullinemia
Congénital lysine intolérance
Isolated neurological distress
Glycine encephalopathy
D-glyceric I acidemia
HMG, hydroxymethylglutaric; CPS, carbamyl-phosphate synthetase; OCT, ornithine-carbamyl transferase; MSUD, maple syrup urine disease.
hydroxylase. It is characterized by a phenylalaninemia exceeding 25 mg/100 ml
(1,500 μιηοΐ/ΐ), normal tyrosinemia, and urinary excrétion of phenylpyruvic and
orthohydroxyphenylacetic acids (PPA and Ο OH PA) when normal protein dietary
conditions exist (3 g/kg/day in the neonatal period). It was Fôlling in 1934 (2) who
discovered PKU, Jervis in 1947 (3) who demonstrated the deficiency in phenylalanine's hepatic hydroxylation, and Mitoma et al. (4) and Kaufman (5,6) who studied the enzyme System responsible for its hydroxylation (Fig. 1). This System involves an enzyme complex associating phenylalanine hydroxylase, dihydropteridine reductase (DHPR), and the cofactors NADH and tetrahydrobiopterin
(5,6). In true PKU, phenylalanine hydroxylase itself is inactive, demonstrating
less than 1% of its normal activity. Two important advances were made in the
treatment of this disorder when Bickel et al. in 1953 (7) demonstrated the efficacy
of a low phenylalanine diet, and when Guthrie and Susi in 1961 (8), proposed a
simple neonatal screening procédure that was accurate and economical.
In France, PKU occurs once in approximately 15,000 births; it is approximately
the same in the United States (9). Besides classical PKU, one can observe atypical
212
1NB0RN ERRORS OF METABOUSM
PROTEINS
•
.
/
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PHENYLPYRUVIC ACID
PARA HYDROXYPHENYLPYRUVIC
ACID
HOMOGENTISICACID
ORTHO-HYDROXYPHENIYL ACETIC ACID
1
PHENYLALANINEHYDROXYLASE
2
PHENYLALANINE TRANSAMINASE
3
TYROSINEAMINOTRANSFERASE
4
PARA HYDROXY PHENYLPYRUVATE OXIDASE
FIG. 1. Simplifiée! schéma of phenylalanine metabolism.
PKU and persistent moderate hyperphenylalaninemias in which the enzymatic defect is less severe. Giittler has published a comprehensive study of the genetic
hypothèses explaining the three principal phenotypes in phenylalanine hydroxylase
deficiency (10).
Clinical Présentation and Diagnosis
The clinical présentation of nontreated PKU has been well defined. The infant
seems completely normal during the neonatal period. In some cases, digestive
problems and vomiting are noted in the first weeks. A delay in psychomotor development and even régressions become évident after several months; convulsive
épisodes are noted in 25% of the cases. Other findings include a depigmentation of
hair and irises, abnormal urine odor described as musty, and fréquent eczematous
cutaneous lésions. In 96% to 98% of the cases, mental deficiency is severe with
an IQ below 50.
When treated early and properly followed, PKU has an excellent prognosis, and
mental deficiency is avoidable. Long-term statistical studies comparing affected
INBORN ERRORS OF METABOUSM
213
children and their nonaffected siblings nonetheless demonstrate a slightly lower IQ
in PKU infants, even when treated early (11). In the early school years, deficiencies in language (12), fine motricity, and temporospatial organization can handicap
the child (13).
The diagnosis of PKU is biological, consisting of the analysis of plasma phenylalanine and tyrosine levels, and the analysis of urinary excrétion of certain metabolites including PPA and Ο OH PA.
Frequently, immaturity in phenylalanine's transamination reaction can delay the
excrétion of PPA. Conversely, one can observe hyperphenylalaninemias caused by
immaturity, or véritable transitory PKU, characterized by a phenylalaninemia exceeding 25 mg/100 ml, normal tyrosinemia, and excrétion of PPA and Ο OH PA
(Table 5). Ail of thèse disorders normalize with time despite the return to a normal
protein diet. The possibility of immaturity and enzymatic variants (14) nécessitâtes
systematic vérification of the diagnosis of true PKU at about 3 months of âge. An
oral phenylalanine loading test (100 mg/kg) can distinguish between true PKU,
atypical PKU, and transitory hyperphenylalaninemia. It is also necessary to systematically eliminate the possibility of hyperphenylalaninemia owing to tetrahydrobiopterin deficiency whether it results from a deficiency in DHPR or in biopterin
synthesis.
Treatment
The treatment of PKU is based on dietary restriction of phenylalanine. However, since phenylalanine is an essential amino acid, the residual intake must remain sufficient (approximately 200-300 mg/24 hr). Phenylalanine tolérance varies
according to the infant and the severity of the enzyme deficiency. Plasma phenylalanine levels are customarily maintained slightly above normal (2-6 mg/100 ml)
in order to avoid the risks associated with deficiency. Thèse risks include anémia,
growth stagnation, anorexia, cutaneous lésions, lethargy, and mental deficiency,
and can be as detrimental as those caused by excess intake. The level at which
phenylalaninemia should be maintained remains a subject of discussion. This type
of restricted diet can be achieved using protein hydrolysates low in phenylalanine
or mixtures of pure amino acids lacking phenylalanine (Table 2). Thèse products
should always be administered along with natural protein sources (small quantities
of milk, for example) to assure a minimal intake of phenylalanine. The follow-up
of treated PKU infants includes periodic clinical and biological control: growth
and weight gain, psychomotor development, and phenylalanine levels. The diet
should be adapted to âge and laboratory findings (introduction of green vegetables,
fruits, and spécial low protein foods: flour, noodles, bread, low protein cookies,
etc.). The dietitian, psychologist, and biologist should collaborate with the pediatrician in treating thèse children. Every patient receiving treatment for PKU must
receive vitamin suppléments and the diet of each patient should be considered
most carefully from this point of view. Some low phenylalanine products do not
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INBORN ERRORS OF METABOUSM
215
contain added vitamins, and it is therefore essential to give the complète supplément each day. The absorption of some minerai éléments, especially calcium and
zinc, may be compromised by the substitution of vegetable proteins for méat and
the exclusion of milk and dairy products from the diet. Concern over trace élément
deficiency was confirmed by the work of Alexander et al. (15) who showed a deficiency of iron, copper, zinc, and manganèse in PKU children receiving a low
phenylalanine diet. A new formulation for trace élément supplementation with an
increased dosage of iron, copper, and zinc was suggested. Despite a daily supplementation with 8 g of a minerai mixture, Taylor et al. (16) still observed signs of
a relative zinc deficiency in hair and plasma of PKU patients that might resuit from
a compétitive inhibition of absorption by copper or other metals supplemented in
the diet. Except for diet restriction, the lives of thèse children should be as normal
as possible (family life, peer contact, schooling, etc.). The majority of authorities
advise discontinuation of dietary restrictions at the âge of 6 or 7 years. Hère again,
some uncertainties persist. A growing number of workers including Bickel (17),
advocate the continuation of strict dietary restriction until the âge of 12. A problem
that will become increasingly important in the years to corne is that of PKU mothers. It has conclusively been proven that children of nontreated PKU mothers suffer from intrauterine growth retardation, microcephaly, mental deficiency, and cardiac malformations. According to Lenke and Levy (18), risks are elevated when
phenylalaninemia levels exceed 15 mg/100 ml. Restricted diets, initiated early in
pregnancy, and maintaining phenylalaninemia below 8 mg/100 ml, might insure
the birth of normal infants. Komrower et al. hâve recently outlined the practical
difficulties of initiating and maintaining such diets in many cases, and hâve emphasized the need for prospective studies in this poorly understood domain (19).
Hyperphenylalaninemias Caused by Tetrahydrobiopterin (BH4) Deficiency
In 1975, Kaufman et al. (20) first reported a case of PKU due to DHPR deficiency in an infant suffering from severe mental deficiency despite dietary restrictions that were initiated early and correctly followed. Since BH4 acts as a cofactor
in other hydroxylation Systems (tyrosine hydroxylase and tryptophan hydroxylase)
necessary for the synthesis of neurotransmitters (DOPA, norepinephrine, serotonin) it was proposed that DOPA, Carbidopa and 5-OH-tryptophan be added to
the phenylalanine restricted diet (27). Two kinds of BH4-deficiencies can be
distinguished (22).
Hyperphenylalaninemias caused by DHPR deficiency
The deficiency in DHPR can be demonstrated in a variety of tissues. Contrary
to phenylalanine hydroxylase deficiency, it can also be demonstrated in cultured
fibroblasts.
216
INBORN ERRORS OF METABOUSM
Hyperphenylalaninemias caused by dihydrobiopterin synthesis deficiency
In 1977, another type of malignant hyperphenylalaninemia was described, characterized by tetraplegia, myoclonic crises, and death despite early dietary restriction and even though phenylalanine hydroxylase and DHPR activities remained
normal. Several case studies since then hâve demonstrated a deficiency in dihydrobiopterin synthesis. This deficiency can resuit from dihydrobiopterin synthetase
or from guanosine-triphosphate (GTP) cyclohydrolase I deficiencies (23).
Some patients with a dihydrobiopterin synthetase deficiency can be treated effectively by BH4 monotherapy (5 mg/kg/day) whereas, in most cases, neurotransmitter precursor supplementation is necessary. Although hyperphenylalaninemias
caused by disorders in biopterin metabolism are relatively rare (1 in 100 cases of
true PKU), their négative évolution and successful treatment by DOPA and 5-OHtryptophan justify routine screening for them in cases of neonatal hyperphenylalaninemia. Several methods hâve been proposed (24). The most promising techniques, both précise and nonaggressive, appear to be assays of reduced and oxidized biopterins in the urine and the biological assay of BH4 in blood using a
Guthrie card (25).
Disorders of the Urea Cycle
Since the description of argininosuccinic aciduria by Allan et al. in 1958 (26),
numerous enzyme disorders affecting the différent stages of ureogenesis hâve been
identified (22): mitochondrial carbamyl-phosphate synthetase (CPSI) deficiency;
ornithine-carbamyl transferase (OCT) deficiency; argininosuccinate synthetase
(ASS) deficiency responsible for citrullinemia; argininosuccinate lyase (ASL) deficiency, responsible for argininosuccinic aciduria; arginase deficiency responsible
for argininemia. Recently a deficiency in N-acetylglutamate synthetase has been
discovered. This enzyme is necessary for the synthesis of N-acetylglutamate,
which, in turn, activâtes CPSI (Fig. 2). The overall prevalence of urea cycle disorders is estimated to be 1 in 3,000 live births. Ail of thèse urea cycle disorders,
except for OCT deficiency, are transmitted in an autosomal récessive manner.
OCT deficiency, the most fréquent of them, is transmitted as a dominant sexlinked trait. Urea cycle disorders are not the only metabolic disorders capable of
giving severe hyperammonemia. Other hereditary metabolic disorders are frequently accompanied by hyperammonemia even in the complète absence of hepatic failure. This is the case in methylmalonic, propionic, isovaleric, and methylacetoacetic acidemias, as well as in pyruvate carboxylase deficiency (28).
Différent mechanisms hâve been proposed to explain the abnormalities in ureogenesis and resulting hyperammonemia encountered in thèse diseases (29). Whatever
the mechanism, when hyperammonemia is paradoxically associated with metabolic
acidosis and ketosis (more often it is associated with alkalosis), investigations
should be oriented toward the organic acidemias. Other disorders can also give
INBORN ERRORS OF METABOUSM
217
Glutamic acid
NH 3 + C 0 2
î
ADP
--,>
CARBAMYL-PHOSPHATE
OROTICACID
Argininosuccinic acid
PYRIMIDINES
1. Carbamyl-phosphate synthetase I
2. Ornithine-carbamyl transferase
IC-PS-I)
(O.C.T. )
3. Argininosuccinate synthetase
4
Argininosuccinate-lvase
5. Arginase
FIG. 2.
Schematic représentation of the urea cycle.
hyperammonemia (Table 6): (a) congénital protein intolérance with hyperlysinuria
caused by abnormalities in the transport of basic amino acids (30), (b) hyperammonemia with hyperornithinemia and homocitrullinuria (31), (c) congénital lysine
intolérance (32), (d) inadéquate portai circulation (porto-caval shunting), transient
hyperammonemia of the prématuré (33).
For each of the enzyme disorders affecting the urea cycle, clinical forms with
varying degrees of severity hâve been reported. Each corresponds to one of
the différent enzyme variants in which enzyme activity can be more or less
diminished.
Neonatal Forms
The neonatal forms are the most severe and are often rapidly fatal. Defective
enzymatic activity is less than 10% of normal in thèse patients, in contrast to children with intermittent forms who hâve greater than 10% of normal activity. After a
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INBORN ERRORS OF METABOUSM
219
symptom-free interval from 1 to several days after birth, the infant begins showing
anorexia, vomiting, progressive altération of consciousness from lethargy to coma,
and convulsions. Laboratory investigations reveal considérable ammonemia at levels substantially higher than those observed in severe hepatic failure, often surpassing 700 μΜ/l. At the same time glutaminemia is elevated, as well as glutamic
acid, alanine, and lysine. Blood urea nitrogen may remain at normal levels despite
defective urea synthesis. Occasionally one observes an increase in transaminases
and a decrease in coagulation factors of hepatic origin. Alkalosis is présent more
often than ketosis or metabolic acidosis. The EEG shows nonspecific diffuse altérations.
The physiological defect in thèse infants is an inability to synthesize and excrète
waste nitrogen in the form of urea. This defect allows nitrogenous precursors of
urea, glutamine, alanine, and ammonium to accumulate. Life-threatening épisodes
of hyperammonemia can be treated with peritoneal or hemodialysis before irréversible damage occurs. In disorders other than arginase denciency, arginine,
which is the only amino acid of the urea cycle to be incorporated into protein,
becomes essential. Plasma arginine levels are low. A low protein diet given without arginine suppléments should increase the tendency toward arginine denciency,
poor growth, and, in turn, reduced utilization of nitrogen, thereby tending to increase hyperammonemia. There is also some évidence that arginine does stimulate
activity of N-acetylglutamate synthetase, an enzyme responsible for production of
N-acetylglutamate, which is the essential cofactor of CPSI. Moreover, as arginine
is the main precursor of ornithine, required for uptake of carbamyl-phosphate, arginine supplementation allows urinary excrétion of both nitrogen atoms (coming
from carbamyl-phosphate and aspartic acid) as argininosuccinic acid in ASL denciency, and of one of them as citrulline in ASS denciency.
Whatever the mechanisms involved, arginine suppléments added to a reduced
protein intake benefit patients with urea cycle defects other than arginase denciency. One should aim at plasma arginine levels of 60 to 100 μπιοΐ/ΐ. In severe
forms of CPS, OCT, and ASS deficiencies, additional measures are necessary.
One approach is to replace natural protein by a mixture of essential L-amino acids.
Another theoretically more effective approach replaces natural protein by a mix­
ture of keto- or hydroxyanalogues of several essential amino acids (leucine, isoleucine, valine, phenylalanine, and methionine) given with a mixture of other essen­
tial amino acids (threonine, lysine, tryptophan, and histidine) and L-arginine.
Thèse approaches allow réduction of nitrogen intake, stimulate nitrogen utilization
for synthesis of nonessential amino acids, and of some of the essential ones, from
their keto-analogues (34). However, high costs of keto-analogue mixtures argue
against their long-term utilization. More promising are treatments with sodium
benzoate and phenylacetate that stimulate urinary waste nitrogen excrétion in the
form of hippuric acid (benzoic acid + glycine) and phenylacetylglutamine (phenylacetic acid + glutamine), greatly decreasing the level of hyperammonemia (35,36).
In the liver mitochondria, the benzoate forms benzoyl-CoA which is excreted with
a high clearance by the kidney. If glycine is low, benzoyl-CoA will accumulate
220
INBORN ERRORS OF METABOUSM
and impair gluconeogenesis, lipid metabolism, and carbamyl-phosphate synthesis:
therefore, benzoate should be used only if organic acidemias hâve been ruled out
as causes of the hyperammonemia. The use of phenylacetate is still expérimental.
Its advantage, in relation to benzoate, is the fact that 2 mol of nitrogen are fixed
per mol of phenylacetate. However, its répulsive smell prevents its pérorai administration at the présent time.
During hyperammonemic coma, an intravenous infusion of sodium benzoate
(250 mg/kg in a 3% solution) and of arginine hydrochloride (800 mg/kg) is followed by constant infusion. Peritoneal dialysis or hemodialysis appears to be much
more efficient than exchange transfusion for ammonia removal. To reduce the catabolic state and endogenous utilization of protein for energy production that increases NH3 production, it is urgent to cover calorie needs with IV administration
of glucose (80 ml/kg/24 hr of 20% glucose with electrolytes) and lipid emulsion
(3 g/kg/24 hr), the latter after organic acidemias hâve been ruled out. Enterai nutrition is undertaken as soon as possible, by continuous naso-gastric infusion, to assure a calorie intake exceeding 120 kcal/kg/24 hr. As soon as ammonemia has
fallen below 200 μπιοΐ/ΐ, a mixture of essential amino acids (0.5-0.7 g/kg) with
added milk protein (0.5-0.7 g/kg) should be given without delay.
Long-term therapy differs according to the spécifie enzymatic defect. In argininosuccinic aciduria, a protein restricted diet (1.5 g/kg/day), supplemented with arginine (0.5-0.7 g/kg/day in 4 divided doses) allows for équilibration.
In citrullinemia, the therapy associâtes essential amino acids (0.5-0.7 g/kg/day),
limited natural protein (0.5-0.7 g/kg/day), arginine (0.5-0.7 g/kg/day), and sodium benzoate (0.25 g/kg/day). Carbohydrates and lipids are provided in order to
maintain calorie intake above 100 kcal/24 hr.
In CPS and OCT deficiencies, citrulline should be used instead of arginine, in
equimolar amounts: 1 mol of nitrogen will be fixed for argininosuccinate synthesis
and released as urea (37).
Acute épisodes of hyperammonemia, sometimes resulting in death, can occur
despite this treatment. The precipitating causes include intercurrent infections or
excessive protein intake. Treatment of thèse épisodes requires intravenous arginine
and benzoate therapy together with peritoneal dialysis or hemodialysis when
required.
Some other treatments hâve been proposed: N-carbamylglutamate, which is an
analogue of N-acetylglutamate, is effective in the treatment of hyperammonemia
due to N-acetylglutamate synthetase deficiency and might improve control of ammonia levels in OCT, ASS, and ASL deficiencies and in the partial deficiency of
CPS (37). In argininemia, secondary to arginase deficiency, a low arginine diet
started in the neonatal period normalizes arginine levels and allows normal intellectual and neurological development. Unfortunately in the neonatal forms of other
urea cycle diseases, the results are far from this successful. Neurological and developmental progress has been variable. Many children hâve delayed intellectual
development; thèse unfortunate outeomes seem correlated with the duration and
the severity of the neonatal hyperammonemic coma.
INBORN ERRORS OF METABOL1SM
221
Glycine Encephalopathy
Neonatologists are familiar with this occurrence because of the rapid onset of
the disease and its severity. The désignation glycine encephalopathy is preferred
over hyperglycinemia without ketosis, initially proposed to contrast this disorder
with the hyperglycinemias with ketosis. The latter is synonymous with several organic acidemias such as propionic and methylmalonic acidemias. In glycine encephalopathy, hyperglycinemia can be moderate or even absent even though glycine levels in the CSF are increased from 10 to 30 times normal values. Glycine
encephalopathy is caused by the inactivity of glycine synthetase, the enzyme necessary for converting glycine to serine. The disease's severity probably stems from
glycine's inhibitory rôle on synaptic transmission. After a free interval of 2 to 3
days after birth, severe neurological symptoms appear: extrême hypotonia, lethargy, and irregular superficial breathing. Respiratory failure often requires ventilatory assistance. The metabolic abnormalities include hyperglycinuria, moderate
hyperglycinemia ranging from 6 to 14 mg/100 ml, and extrême increases in CSF
glycine levels ranging from 1 to 2 mg/100 ml (N, 0.06 ±0.01 mg/100 ml). A major élément in the diagnosis is the EEG demonstrating a flat tracing interrupted
pseudoperiodically by bursts of sharp wave activity. The prognosis is not favorable. Should the infant survive the initial period of respiratory failure, thanks to
modem methods of ventilatory assistance, severe mental deficiency with microcephaly and convulsions are nonetheless unavoidable. EEG findings subsequently
evolve toward hypsarythmia. Différent therapeutic approaches hâve been tried separately or together: exchange transfusion or peritoneal dialysis during acute épisodes; semisynthetic low glycine-serine diet; choline, folie acid, N5-formyltetrahydrofolate; methyl-serine; administration of sodium benzoate or ursodesoxycholic
acid to increase glycine élimination (38).
Treatment with strychnine, a spécifie antagonist of the glycine System in the
CNS proposed by Gitzelmann et al. (39) has given better results even though it
does not prevent severe mental retardation (40). D-glyceric acidemia described by
Brandt and co-workers (41) appears with a very similar clinical and biochemical
picture.
Branched-Chain Amino Acid Disorders
A great number of inborn errors of branched-chain amino acid metabolism hâve
been described, nearly at every step of their catabolism (Fig. 3).
Several variants of thèse diseases may be vitamin responsive: MSUD, thiamin
responsive (20 mg/day) (42); MM A, vitamin B,2 responsive; PA, biotin responsive
(10 mg/day), belonging in fact to a multicarboxylase deficiency with accumulation
of other organic acids (3 methylcrotonylglycine, pyruvic, lactic, and 3 hydroxyisovaleric acids). Vitamin therapy must be systematically tested even if, in severe
neonatal forms, vitamin dependency is rarely observed (43). As in urea cycle dis-
INBORN ERRORS OF METABOLISM
222
I
-t
a-KETO 0 METHYLVALEfitC ACID
ETHYL>
ι KÊTOISOCAPflOIC ACID
*'
ISOVALERYL-CoA
a-METHYLBUTYRYL-CoA
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ο METHYL β-HYDROXYBUTYRYL CoA
*'
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β HYDROXY-p-METHYLGLUTARYL CoA
(S-HYDROXYISOBUTYRYL-CQA
ISOBU
0 HYDROXYISOBUTYRIC ACID
I
a-METHYLACETOACETYL CoA
ACETOACETICACID
1. HYPERVALINEMIA (VAL1NE TRANSAMINASEJ
2
'ISOVALE
a KETOISOVALEHIC
ACID
METHYLMALONIC SEMIALDEHYDE
PROPION YL-CoA
MAPLE SYRUP UfilNE DISEASE IBRANCHED KETOACIDS DECARBOXYLASE)
3
ISOVALERIC ACIDEMIA (ISOVALERYL-CoA ÛEHYDROGENASE I
4
Jl METHYLCROTONYL GLYCINURIA (β-METHYLCROTONYL CoACARBOXYLASE
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'LMALOh
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L METHYLMAUONYL-CoA
'LMALON
5. 3 METHYLGLUTACONIC ACIDURIA |3 MG-CoA HYDRATASE I
6. β-ΗΥΟΗΟΧΥ-0-METHYLGLUTARIC ACIDURIA (HMG-CoA t-YASE)
7
SUCCINYL-CoA
METHYLACETOACETIC ACIDURIA IK DEPENDENT KETOTHIOLASEI
B. PROPIONIC ACIDURIA j PROPION YL-CoA CARBOXYLASE1
9
METHYLMALONIC ACIDURIA IMM-CoA RACEMASE)
10
METHYLMALONIC ACIDURIA IMM-CoA MUTASEI
FIG. 3. Hereditary diseases of branched-chain amino acid metabolism.
orders, the emergency treatment of branched-chain amino acid disorders during the
acute phase has two mean goals: removal of toxic metabolites and anabolism.
The more effective methods for removal differ, according to the toxic organic
acids or amino acids accumulated; peritoneal dialysis associated with exchange
transfusions in MSUD and in PA, forced diuresis and exchange transfusions in
MMA, glycine supplementation in IVA (43). Carnitine supplementation may also
be important to remove and to eliminate toxic organic acids such as acetylcarnitines in MMA, PA, IVA, 3 hydroxy-3-methylglutaric aciduria, and β keto-thiolase
deficiency (44). The arrest of catabolism and the promotion of anabolism needs a
high calorie intake. Continuous enterai nutrition by a naso-gastric tube must be
begun as soon as possible with carbohydrates (glucose and glucose polymers), lipids, vitamins, minerais, and precursor free amino acid mixtures. Precursor amino
acids may be introduced in limited amounts after lowering of toxic metabolites.
The long-term outeome of patients with thèse disorders is still disappointing when
they are vitamin unresponsive. Many children die secondarily during an acute crisis, and many of the survivors are mentally retarded. A good outeome is possible
for patients with MSUD if diagnosis is made early and treatment begun (45).
MSUD
Symptoms appear when plasma levels of the branched amino acids and their
corresponding alpha-keto-acids increase, particularly when leucine levels exceed
INBORN ERRORS OF METABOUSM
223
10 to 12 mg/100 ml. Treatment consists of maintaining the branched amino acid
concentrations at approximately normal levels by implementing diets low in leucine, isoleucine, and valine. Since thèse three essential amino acids are necessary
for normal protein synthesis, a minimal quantity of leucine, isoleucine, and valine
must be présent in the diet. It is advisable to maintain the plasma levels of thèse
three amino acids between 2 and 5 mg/100 ml, slightly higher than the normal
values. In the classical acute form leucine tolérance is situated between 200 and
600 mg/day. Ail alimentary proteins contain substantial quantities of branched
amino acids. Therefore, dietary restriction nécessitâtes the utilization of semisynthetic diets in which protein requirements are essentially provided by amino acid
mixtures totally lacking the three branched amino acids. Natural proteins must be
strictly limited to quantities corresponding to the infant's tolérance to branched
amino acids. Requirements in water, minerais, trace éléments, vitamins, fats, and
carbohydrates must not be neglected. During periods of decompensation, high levels of branched amino acids (especially leucine) should be rapidly lowered to less
than 10 mg/100 ml. Peritoneal dialysis has been shown to be the most effective
technique—even more effective than exchange transfusion. Dialysis sessions
should not exceed 48 hr. When treatment is initiated early enough (within the first
10 days after birth) and when a satisfactory equilibrium is rapidly obtained and
maintained, results tend to be excellent with normal intellectual development. The
best results are obtained when there is a previous family history of MSUD. In
thèse cases, the diagnosis is usually made much earlier, before appearance of clinical findings. Such was the case in three out of six personal observations.
In the subacute and moderate forms of MSUD, branched amino acid tolérance
is considerably higher than in the classical acute form. Leucine tolérance ranges
from 900 to 1,200 mg/day. In certain patients, a simple low protein diet is an adéquate therapy. In the intermittent forms of MSUD normal protein diets can be
maintained provided that protein intake is diminished or abolished during periods
of infection or stress causing excessive catabolism.
DISORDERS OF CARBOHYDRATE METABOLISM
Thèse disorders include glycogenoses, glycogen synthetase deficiency, fructose
and galactose intolérances, and enzyme disorders affecting gluconeogenesis such
as type I glycogen storage disease and fructose-1, 6-diphosphatase and pyruvate
carboxylase deficiencies. Furthermore certain enzyme defects in amino acid metabolism and fatty acid beta-oxidation (Table 4) can cause severe hypoglycemia.
Galactosemia
Galactosemia is a récessive autosomal disorder described by Goppert in 1917.
Galactose-1-phosphate uridyl transferase deficiency was established by Kalckar
et al. in 1956 (46). Its frequency is approximately 1 in 55,000 newborns. The
affected infant usually appears normal at birth and symptoms develop within 3 or
224
INBORN ERRORS OF METABOUSM
4 days after institution of milk feeding. The early manifestations include jaundice,
anorexia, vomiting, hypotonia, hepatomegaly, and susceptibility to infection.
Escherichia coli septicemia is not uncommon in thèse infants. Ophthalmologic examination demonstrates cataracts, and ail patients hâve some rénal tubular involvement characterized by proteinuria, generalized amino aciduria, and tubular acidosis. There is frequently hypermethioninemia, tyrosinemia, and tyrosyluria due to
hepato-cellular insufficiency. The absence of succinylacetone in urine allows for
the differential diagnosis with true tyrosinosis. Without treatment the hepato-cellular damage worsens; splenomegaly, ascites, edema, and hemorrhagic phenomena
supervene and death occurs rapidly, subséquent to infection or hepatic failure.
Absence of galactose-1-phosphate uridyl transferase activity in erythrocytes can
be shown provided that the child has not been recently transfused. In such circumstances, the démonstration of a partial enzymatic deficiency in both parents' erythrocytes may be helpful for diagnosis.
Dietary management in galactosemia aims to suppress, as completely as possible, galactose from the diet, to avoid the accumulation of galactitol and galactose1-phosphate (Fig. 4). As cataracts are the only pathological manifestation in galactokinase deficiency—one step earlier in galactose metabolism—galactose-1-phos-
GALACTOSE
UTP
1 GALACTOKINASE
2. GALACTOSE - 1 • P0 4 - URIDYL TRANSFERASE
3. U.D.P GLUCOSE 4 EPIMERASE
4 and 5- U.D.P GLUCOSE and U.D.P. GALACTOSE
PYROPHOSPHORYLASE (presumed lo be identicall
FIG. 4.
Galactose metabolism.
1NBORN ERRORS OF METABOLISM
225
phate accumulation appears as the main toxic compound for the liver, kidney, and
brain. Galactose-1-phosphate inhibits phosphoglucomutase, pyrophosphorylase,
and possibly glycogen phosphorylase. Galactose-1-phosphate accumulation probably induces a trapping of phosphorus with dégradation of adenine nucleotides resulting in increased urea production and impaired energy metabolism.
Total élimination of galactose from the diet appears to be without adverse effects, despite its présence in a number of important body compounds as galactosphingolipids. In fact, the donor molécule of galactose during biosynthesis of thèse
molécules (UDP galactose) can be synthesized from UDP glucose.
Elimination of galactose is accomplished primarily by avoidance of milk and
dairy products, which can be replaced by lactose-free milk substitutes. Beetroots,
peas, liver, brain, sweetbread, or any organ méats are excluded as well as commercial food products that may contain lactose or galactose.
The immédiate effect of treatment is dramatic. Early treatment prevents liver
and kidney failure, brain damage, and cataracts. Over a long term, total exclusion
of galactose from the diet provides satisfactory growth and health. However, despite early and well-followed treatment, many galactosemic children achieve only
a low normal intelligence and expérience speech defects or visual perception difficulties. Most children make less intellectual progress than, for example, welltreated phenylketonurics. Furthermore, in galactosemic girls, the secondary risk of
ovarian dysfunction appears to be important (47). Prénatal accumulation of galactose-1-phosphate and galactitol has been demonstrated in the galactosemic fétus
after abortion (48); this fact could well explain thèse disappointing results. According to Gitzelmann and Steinmann (47), biosynthesis of galactose-1-phosphate
from UDP glucose via UDP glucose-4-epimerase and UDP glucose-pyrophosphorylase (Fig. 4) might constitute a pathway for self-intoxication, not only
in utero, but also later on.
Fructose Intolérance
Hereditary fructose intolérance is an autosomal récessive disorder characterized
by a primary deficiency of hepatic aldolase (aldolase B) (Fig. 5). Most symptoms
are explained by the accumulation of fructose-1-phosphate in those cells that metabolize fructose, namely hepatocytes, enterocytes, and rénal tubular cells. Fructose itself has no toxicity, as demonstrated by fructokinase deficiency, a metabolic
disorder characterized by essential fructosuria, without any clinical symptoms.
Symptoms occur when fructose, saccharose, or sorbitol are introduced in the diet.
The classical case history is that of an infant that has been nursed for 3 or 4
months and is perfectly well. When vegetables, orange juice, or saccharose are
added to the diet, the child begins to vomit, to be drowsy and léthargie after
meals, and fails to thrive. If the diagnosis is not quickly suspected, severe liver
damage will occur, with hepatomegaly, hemorrhages, lethargy, and, sometimes,
edema, ascites, and splenomegaly. Jaundice may or may not be présent. In older
226
INBORN ERRORS OF METABOUSM
children and adults the diagnosis may be easier; the patients refuse anything sweet
as they hâve already experienced nausea, vomiting, sweating, and dizziness after
eating sweet food.
The diagnosis can easily be made by an intravenous fructose tolérance test (0.25
g/kg) that induces hypoglycemia and hypophosphatemia. Enzymatic deficiency
may be demonstrated by liver biopsy or, more easily now, by small intestinal
biopsy (49).
Therapy is simple and consists of the total élimination of fructose and ail potential sources of fructose from the diet. Before using any formula, any drug, or any
parenteral fluid, one should check carefully and make sure that it does not contain
fructose (lévulose), sorbitol, or saccharose. As ail fruits, fruit juices, and a great
number of vegetables are excluded, ascorbic acid supplementation may be proposed, even though vitamin C deficiency has not been reported in such patients.
Gluconeogenesis Disorders
Fructose-1, 6-Diphosphatase Deficiency
This autosomal récessive disease involves a one-way enzyme of gluconeogenesis permitting the cleavage of fructose-1, 6-diphosphate to fructose-6-phosphate
(Fig. 5). Affected children remain euglycemic for 12 to 16 hr after the last meal
until glycogen stores are depleted, after which they become hypoglycémie. A main
problem in thèse children is lactic acidosis. The liver lacks the physiologie capacity to take up lactate originating from muscle, as well as glycerol released from
adipose tissue, and to convert them into glucose. Fasting, stress, muscular exercise, and infections precipitate lactic acidosis and, secondarily, hypoglycemia.
—^
GALACTOSE 1 PO,
GLUCOSE 1 P0 4
'
FRUCTOSE
^
FRUCTOSE 1 PHOSPHATE
FRUCTOSE 6 PHOSPHATE
}
!
FHUCTOKINASE
4
G Î U C O S E 6 PHOSPHATASE
J FRUCTOSE 1 PHOSPHATEALDOLASE
5
PTRUVATE CARBOXVLASE
3
6
PHOSPHOENQLPVRUVATE
FRuCTOSL 1 6 DIPHOSPHATASE
FIG. 5
41
GLUCOSE β P O „
FRUCTOSE 1 6 DIPHOSPATE
CARBOX¥K!NASE
Fructose metabolism and gluconeogenesis disorders.
INBORN ERRORS OF METABOUSM
227
Thèse children do not tolerate (but without aversion for sweet-tasting foods) fructose, which précipitâtes hypoglycemia, by the same mechanism as in fructose intolérance. An intravenous fructose tolérance test induces hypoglycemia and hypophosphatemia, somewhat less severe than in fructose-1-phosphate aldolase
deficiency. Therapeutic management of the disease is much more difficult than in
fructose intolérance. Besides fructose exclusion, the treatment consists of fréquent
feedings, every 2 to 3 hr, and active treatment of infections that can lead to severe
lactic acidosis and hypoglycemia. In such circumstances continuous glucose infusions by naso-gastric tube or IV perfusion may be necessary.
Glycogenosis Type I
Glycogen storage disease type I (Von Gierke disease) occurs because of the congénital inactivity of the key hepatic enzyme glucose-6-phosphatase that is normally
active in hepatocytes, rénal tubular cells, and enterocytes. Individuals with the disease are unable to release free glucose into the blood and become hypoglycémie
2.5 to 3 hr after a meal. They accumulate glycogen and triacylglycerol in their
liver and are unable to convert fructose and galactose into glucose (Fig. 5).
Growth retardation, hepatomegaly, bleeding tendency, hyperlactacidemia, hyperuricemia, and hyperlipidemia are the other main features of the disease.
Stimulation tests with glucagon, epinephrine, galactose, and fructose clearly indicate that glucose cannot be released from glucose-6-phosphate. Since 1959, several cases hâve been reported in which in vitro glucose-6-phosphatase activity of
frozen liver was normal, despite typical clinical and biological features. In such
cases, named pseudotype I glycogenosis, repeated bacterial infections hâve been
reported related to neutropenia, due to arrest of bone marrow maturation, and to
neutrophil dysfunction (50). In thèse pseudo-type I glycogenoses, the apparently
normal glucose-6-phosphatase activity disappears when enzymatic activity is assayed on intact microsomes coming from fresh unfrozen liver. A defect in glucose6-phosphate translocase, an enzyme that transports glucose-6-phosphate inside the
microsome, has been demonstrated by Lange et al. (51). More recently, Nordlie
et al. (52) reported another enzymatic type of pseudotype I glycogenosis, which
they proposed to name type le glycogenosis.
Whatever the exact enzymatic type, la, b, or c, the primary aim of treatment is
to maintain glucose levels as well as possible. Since 1974, numerous publications
hâve demonstrated that continuous nocturnal intragastric feeding, accounting for
one-third of the total calorie intake, combined with fréquent daytime feeding, has
prevented hypoglycemia and improved both growth and metabolic abnormalities.
However, elevated blood lactate and triglycéride levels are not always completely
corrected. Particular attention must be paid in the morning at the end of intragastric infusion, because of the particular risk of hypoglycemia at this time. Children
must be fed within 30 min after the cessation of intragastric infusion. Fructose and
galactose must be maintained as low as possible in the diet as they are unable to
produce free glucose. Recently Smit et al. (53) hâve shown the advantage of slow
228
INBORN ERRORS OF METABOUSM
release carbohydrate such as uncooked cornstarch (2 g/kg) diluted in water, which
maintains glucose levels for 6.5 to 9 hr. Uncooked cornstarch may be an effective
alternative regimen when continuous nocturnal intragastric infusion is refused or
badly tolerated.
DISORDERS OF FATTY ACID METABOLISM
In the last several years, a number of hereditary metabolic disorders affecting
beta-oxidation hâve been reported. They are characterized by vomiting, altérations
in consciousness, hepatomegaly, metabolic acidosis, elevated free fatty acids
(FFA), and severe hypoglycemia without ketosis. Fat accumulâtes in liver and
muscle. Thèse disorders présent acute neonatal forms, fatal within several days,
as in certain cases of type 2 glutaric aciduria and C 6 -d 4 dicarboxylic aciduria, or
intermittent forms in which clinical, biological, and histological findings resemble
those found in Reye syndrome (54).
The patient's basic problem is the inability to maintain sufficient energy metabolism in circumstances with glucose depletion. The defective fatty acid oxidation
induces defective hepatic gluconeogenesis (55) that, associated with a vanished
sparing effect from the ketone bodies (56), is responsible for severe hypoglycemia.
Treatment of thèse children aims at preventing starvation and, during acute épisodes, at restoring as swiftly as possible normal glycémie levels via intravenous
infusion of glucose.
Type 2 Glutaric Aciduria
The disorder type 2 glutaric aciduria (57,58), also termed ethylmalonic aciduria
(59), is caused by a deficiency in acyl-CoA dehydrogenase activity that simultaneously affects the catabolism of organic acids derived from branched-chain amino
acids (isovaleric, isobutyric, alpha-methylbutyric acids) and tryptophan (glutaric
acid) as well as the catabolism of medium-chain fatty acids (C6-C10 dicarboxylic
aciduria) and butyric acid. The manifestations of this organic acidemia are very
similar to those observed in Jamaican vomiting sickness, caused by hypoglycin, a
végétal toxin that inhibits the same acyl-CoA dehydrogenases (60). Type 2 glutaric
aciduria présents either as a severe neonatal form with vomiting, coma, sweaty
feet odor, hypoglycemia, hyperammonemia, and metabolic acidosis (57,58,61), or
as an intermittent form evolving in épisodes of nonketotic hypoglycemia (62). Investigations indicate that the dehydrogenase apoenzyme is intact and that the defects are probably localized on the common flavoproteins (57,63).
Nonketotic C 6 -C u Dicarboxylic Aciduria
Nonketotic dicarboxylic aciduria is not a well-defined disease, but indicates dicarboxylic aciduria that is seen in congénital defects related to the beta-oxidation
of fatty acids. It stands in contrast to the ketotic dicarboxylic aciduria observed in
INBORN ERRORS OF METABOUSM
229
diabètes or starvation where beta-oxidation is increased and accompanied by ketonuria and C6-C8 dicarboxylic aciduria resulting from omega-oxidation of FFA.
This entity clinically manifests itself as épisodes of lethargy or coma with hypoglycemia. The first patient reported died on the first day of life with lactic acidosis
and C6-C)4 dicarboxylic aciduria (64). Five other patients survived the neonatal
period but subsequently suffered a number of Reye syndrome-like attacks (65-67).
The enzymatic defect probably involves the medium-chain acyl-CoA dehydrogenase.
In 1977, Tanaka et al. (68) reported an observation characterized by acute crises
with hypoglycemia, hyperammonemia, adipic aciduria, and mild Cg-Cio dicarboxylic aciduria related to a butyrl-CoA dehydrogenase deficiency.
Systemic Carnitine Deficiency
This disorder manifests itself in a similar manner, with épisodes of acute encephalopathy, vomiting, lethargy, coma, hepatic failure, metabolic acidosis, nonketotic hypoglycemia, hepatic steatosis, and lipid myopathy. In acute crises, findings resemble those in Reye syndrome. Muscular weakness and predominantly
proximal amyotrophy can be présent. Thèse abnormalities are due to a severe carnitine deficiency. Another finding, although inconstant, is C6-Ci0 dicarboxylic
aciduria (69-71). Uncertainty still remains as to the origin of the carnitine deficiency (72). Whatever it may be, carnitine therapy may be bénéficiai.
Carnitine Palmitoyl Transferase Deficiency
In the forms generally observed in adulthood (73), this disorder is primarily
characterized by muscular abnormalities including muscular pain and myoglobinuria after strenuous physical activity. In the more commonly cited adolescent or
adult forms, carnitine palmitoyl transferase (CPT) deficiency appears only to affect
skeletal muscle while leaving other metabolic sites intact. Recently however,
Bougnères and co-workers (74) reported an infant suffering from hepatic CPT deficiency responsible for fasting hypoglycemia and hypoketonemia. Mention should
also be made of three cases reported by Hermier et al. (75) in which an encephalopathy was associated with CPT deficiency.
DISORDERS IN THE METABOLISM OF TRACE ELEMENTS
Our understanding of the metabolism and physiological rôle of trace éléments
has been increasing rapidly. A number of pathological entities hâve been attributed
to trace élément disorders essentially involving iron, iodine, zinc, copper, sélénium, and chromium. The rôle of other trace éléments such as cadmium, vanadium, molybdenum, and manganèse has also recently received attention.
Trace éléments intervene in various domains including hematopoiesis, immu-
230
INBORN ERRORS OF METABOUSM
nity, thyroid hormones, metalloenzymes, oxidoreduction, glycoregulation, etc.
We shall discuss only two hereditary disorders in trace élément metabolism encountered in infancy: acrodermatitis enteropathica and Menkes disease.
Acrodermatitis Enteropathica
This rare autosomal disorder appears in the first months after birth and is fatal
when untreated (76). It is characterized by chronic diarrhea, hypotrophy, alopecia,
periorificial and distal erythemato-squamous dermatitis, and récurrent infections.
Zinc levels are usually low in blood, erythrocytes, and hair follicles (77). Metalloenzymes such as alkaline phosphatase are decreased. Zinc malabsorption is probably due to abnormalities in a zinc binding factor of enterocytic origin. The reason
for the therapeutic efficacy of human milk compared with the deleterious effect of
cow's milk has not been elucidated and has stimulated research in the rôle of exogenous binding factors.
Oral treatment with zinc sulfate (100 mg/day in divided doses) is rapidly effective. This treatment should be continued indefinitely, especially in pregnant patients, since zinc deficiency can cause abortion and malformations.
Menkes Disease
Also termed kinky-hair or, more exactly, steely-hair disease, Menkes disease is
a rare récessive X-linked disorder affecting copper metabolism (78,79). Soon after
birth, patients présent with a convulsive encephalopathy, abnormal (pili torti) and
depigmented (steely) hair, hypothermia, growth deficiency, characteristic facial
dysmorphy, and bone lésions (osteoporosis and metaphyseal fractures). It is characterized by many of the features of copper deficiency but apparently without neutropenia and anémia. Death usually occurs before 2 years of âge. The copper deficiency is caused by its abnormal intestinal absorption associated with its
accumulation in gut mucosa. A large proportion of the small amount of copper
absorbed accumulâtes in the kidney, probably during reabsorption in the rénal
tubules.
Treatment is based on parenteral administration of copper, which raises plasma
copper and ceruloplasmin to normal but does not correct other facts of the disease.
It may be more effective if initiated soon after birth.
REFERENCES
1. Dobbing J, Sands J. The quantitive growth and development of the human brain. Arch Dis Child
1973;48:757-67.
2. Fôlling A. Uber Auscheidung von Phenylbrenztraubensaiire in den Harn als Stoffwechsel Anomalie in Verbindung mit Imbezillitât. Ζ Physiol Chem 1934;227:169-76.
3. Jervis GA. Studies of phenylpyruvic oligophrenia: the position of the metabolic error. J Biol
Chem 1947:169:651-6.
INBORN ERRORS OF METABOUSM
231
4. Mitoma L, Auld RM, Udenfriend S. On the nature of enzymatic defect in phenylpyruvic oligophrenia. Proc Soc Exp Biol Med 1957;94:634-5.
5. Kaufman S. Phenylalanine hydroxylase cofactor in phenylketonuria. Science 1958;128:1506.
6. Kaufman S. The phenylalanine hydroxylating System in phenylketonuria and its variants. Biochem
Med 1974;85:55-9.
7. Bickel H, Gerrard J, Hickmans EM. Influence of phenylalanine intake on the chemistry and behavior of a phenylketonuric child. Acta Pediatr 1954;43:64-77.
8. Guthrie R, Susi A. A simple phenylalanine method for detecting phenylketonuria in large populations of newborn infants. Pediatrics 1963;32:338-43.
9. Veale AMO. Screening for phenylketonuria In: Bickel H, Guthrie R, Hammersen, G, eds. Néonatal screening for inborn errors of metabolism. Berlin: Springer Verlag, 1980:7-18.
10. Guttler F. Hyperphenylalaninemia: diagnosis and classification of the various types of phenylalanine hydroxylase deficiency in childhood. Acta Paediatr Scand [Suppl] 1980;280:1-80.
11. Rey J, Rey F. Phénylcétonurie et développement mental: un problème mal posé. Arch Fr Pédiatr
1978;35:3-10.
12. Melnick CR, Michals KK, Matalon R. Linguistic development of children with phenylketonuria
and normal intelligence. J Pediatr 1981; 98:269-72.
13. Rappaport D, Saudubray JM, Hatt A, et al. Etude psychologique de 20 enfants phénylcétonuriques traités tôt. Ann Pédiatr (Paris) 1975;22:509-16.
14. Rey F, Leeming RJ, Curtius H Ch, Niederwieser A, Viscontini M, Rey J. La phénylcétonurie
"transitoire." Un déficit permanent. Arch Fr Pédiatr 1979;36:48-55.
15. Alexander FW, Clayton BE, Delves HT. Minerai and trace métal balances in children receiving
normal and synthetic diets. Q J Med 1974;43:89-111.
16. Taylor JC, Moore G, Davidson DC. The effect of treatment on zinc, copper and calcium status
in children with phenylketonuria. J Inherited Metab Dis 1984;7:160-4.
17. Bickel H. Phenylketonuria: past, présent, future. J Inherited Metab Dis 1980;3:123-32.
18. Lenke RR, Levy HL. Maternai phenylketonuria and hyperphenylalaninemia. Ν Engl J Med
1980;303:1202-8.
19. Komrower GM, Sardharwalla IB, Coutts JMJ, Ingham D. Management of maternai phenylketon­
uria: an emerging clinical problem. Br Med J 1979;1:1383-7.
20. Kaufman S, Holtzman NA, Milstien S, Butler IJ, Krumholz A. Phenylketonuria due to a defi­
ciency of dihydropteridine reductase. Ν Engl J Med 1975;293:785-90.
21. Curtius H Ch, Niederwieser, A, Viscontini M, et al. Atypical phenylketonuria due to tetrahydrobiopterin deficiency. Diagnosis and treatment with tetrahydrobiopterin, dihydrobiopterin and sepiapterin. Clin Chim Acta 1979;93:251-62.
22. Rey F, Harpey JP, Leeming RJ, Blair JA, Aicardi J, Rey J. Les hyperphénylalaninémies avec
activité normale de la phenylalanine hydroxylase: le déficit en tétrahydrobioptérine et le déficit
en dihydrobioptérine reductase. Arch Fr Pédiatr 1977;34:109-20.
23. Niederwieser A, Blau N, Wang H, Joller P, Antares M, Cardesa-Garcia J. G.T.P. cyclohydroxylase I deficiency, a new enzyme defect causing hyperphenylalaninemia with neopterin, biopterin,
dopamine and serotonine deficiencies and muscular hypotonia. Eur J Pediatr 1984;141:208-14.
24. Berlow S. Progress in phenylketonuria: defects in the metabolism of biopterin. Pediatrics
1980;65:837-9.
25. Leeming RJ, Barford PA, Blair JA, Smith I. Blood spots on Guthrie cards can be used for inherited tetrahydrobiopterin deficiency screening in hyperphenylalaninaemic infants. Arch Dis Child
1984;59:58-61.
26. Allan JD, Cusworth DC, Dent CE, Wilson VK. A disease probably hereditary characterized by mental deficiency and a constant gross abnormality of amino acid metabolism. Lancet 1968;1:182-7.
27. Farriaux JP. Le cycle de l'urée et ses anomalies. Paris: Doin, 1978.
28. Vidailhet M, Lefebvre E, Marsac C, Beley G. Congénital lactic acidosis with pyruvate carboxylase inactivity. J Inherited Metab Dis 1984;4:131-2.
29. Coude FX, Sweetman L, Nyhan WL. The inhibition by propionyl coenzyme A of N-acetylglutamate synthetase in rat liver mitochondria. A possible explanation for hyperammonemia in
propionic and methylmalonic acidemia. J Clin Invest 1979;64:1544-51.
30. Simell O, Perheentupa J, Rapola J, Visakorpi JK, Eskelin LE. Lysinuric protein intolérance. Am
J Med 1975;59:229-40.
31. Shih VE, Efron ML, Moser HW. Hyperomithinemia, hyperammonemia and homocitrullinuria. A
new disorder of amino-acid metabolism associated with myoclonic seizures and mental retardation. J Dis Child 1969;117:83-92.
232
INBORN ERRORS OF METABOUSM
32. Colombo JP, Burgi W, Richterich R. Congénital lysine intolérance with periodic ammonia intoxication. A defect in L-lysine dégradation. Metabolism 1967;16:910-25.
33. Eggermont E, Devlieger H, Marchai G, et al. Angiographie évidence of low portai liver perfusion
in transient neonatal hyperammonemia. Acta Paediatr Belg 1980;33:163-9.
34. Smith I. The treatment of inborn errors of the urea cycle. Nature 1981; 291:378-80.
35. Brusilow S, Tinker J, Batshaw ML. Amino-acid acylation; a mechanism of nitrogen excrétion in
inborn errors of urea synthesis. Science 1980;207:659-61.
36. Batshaw ML, Brusilow S, Waber L, et al. Treatment of inbom errors of urea synthesis. Activation of alternative pathways of waste nitrogen synthesis and excrétion. N Engl J Med
1982;306:1387-92.
37. Bachmann C. Treatment of congénital hyperammonemias. Enzyme 1984;32:56-64.
38. Schoos-Barbette S, Gérard J, Francotte N, Lambotte C. A treatment of non-ketotic hyperglycinaemia. J lnherited Metab Dis 1984;7:165-7.
39. Gitzelmann R, Steinmann B, Otten A, et al. Non ketotic hyperglycinemia treated with strychnine,
a glycine receptor antagonist. Helv Paediatr Acta 1977;32:517-25.
40. Warburton D, Boyle RJ, Keats JP, Vohr B, Pueschel S, Oh W. Non ketotic hyperglycinemia.
Effects of therapy with strychnine. Am J Dis Child 1980;134:273-5.
41. Brandt JN, Rasmussen K, Brandt S, K0lvraa S, Schondeyder F. D-glyceric acidemia and non
ketotic hyperglycinemia. Clinical and laboratory findings in a new syndrome. Acta Paediatr
Scand 1976;65:17-22.
42. Scriver CR, Mackenzie S, Clow CL, Delvin E. Thiamine-responsive maple syrup urine disease.
Lancet 1971;1:310-2.
43. Saudubray JM, Ogier H, Charpentier C, et al. Neonatal management of organic acidurias. Clinical update. J lnherited Metab Dis 1984;7:2-9.
44. Chalmers RA, Stacey TE, Tracey BM, et al. L-carnitine insufficiency in disorders of organic acid
metabolism. Response to L-carnitine by patients with methyl-malonic aciduria and 3-hydroxy3-methyl glutaric aciduria. J lnherited Metab Dis 1984;7:109-10.
45. Léonard JV, Daish P, Naughten ER, Bartlett K. The management and long-term outeome of organic acidaemias. J lnherited Metab Dis 1984;7:13-7.
46. Kalckar HM, Anderson EP, Isselbacher KJ. Galactosemia, a congénital defect in a nucleotide
transferase: a preliminary report. Proc Natl Acad Sci USA 1956;42:49.
47. Gitzelmann R, Steinmann B. Galactosaemia: how does long-term treatment change the outeome?
Enzyme 1984;32:37-46.
48. Ng WG, Donnell GN, Bergren WR, Alfi O, Golbus MS. Prénatal diagnosis of galactosemia. Clin
Chim Acta 1977;74:227-35.
49. Shin YS, Moro V, Doliwa H, Endres W. A radioisotopic method for fructose-1-phosphate aldolase assay that facilitâtes diagnosis of hereditary fructose intolérance. Clin Chem 1983;29:
1955-8.
50. Schaub J, Heyne K. Glycogen storage disease type Ib. Eur J Pediatr 1983;140:283-8.
51. Lange AJ, Arion WJ, Beaudet AL. Type lb glycogen storage disease is caused by a defect in
the glucose-6-phosphate translocase of the microsomal glucose-6-phosphate System. J Biol Chem
1980;255:8381^1.
52. Nordlie RC, Sukalski KA, Mufioz JM, Baldwin JJ. Type le, a novel glycogenosis. Underlying
mechanism. J Biol Chem 1983;258:9793-4.
53. Smit GPA, Berger R, Potasmck R, Moses SW, Fernandes J. The dietary treatment of children
with type I glycogen storage disease with slow release carbohydrate. Pediatr Res 1984; 18:
879-81.
54. Neimann N, Vidailhet M, Grun G, Alba G. Insuffisance hépatique aiguë de l'enfant avec stéatose
viscérale et encéphalopathie (syndrome de Reye). Ann Pediatr (Paris) 1975;22:195-202.
55. Ruderman N, Shafrir E, Bressler R. Relation of fatty acid oxidation to gluconeogenesis. Effect
of pentenoic acid. Life Sci 1968;7:1083-9.
56. Robinson AM, Williamson DH. Physiological rôles of ketone bodies as substrates and signais in
mammalian tissues. Physiol Rev 1980;60:143-87.
57. Goodman SI, McCabe ERB, Fennessey PV, Mace JW. Multiple acyl-CoA dehydrogenase deficiency (glutaric aciduria type II) with transient hypersarcosinemia and sarcosinuria; possible inherited deficiency of an électron transfer flavoprotein. Pediatr Res 1980;14:12-7.
58. Przyrembel H, Wendel V, Becker K, et al. Glutaric aciduria type 2: a report on a previously
undescribed metabolic disorder. Clin Chim Acta 1976;66:227-39.
59. Mantagos S, Genel M, Tanaka K. Ethylmalonic-adipic aciduria. In vivo and in vitro studies indi-
INBORN ERRORS OF METABOUSM
60.
61.
62.
63.
64.
65.
66.
67.
68.
69.
70.
71.
72.
73.
74.
75.
76.
77.
78.
79.
233
cating deficiency of activities of multiple acyl-CoA dehydrogenases. J Clin lnvest 1979;64:
1580-9.
Tanaka K. Disorders of organic acid metabolism. In: Gaull GE, éd. Biology of brain dysfunction.
New York: Plénum Press, 1975:145-214.
Sweetman L, Nyhan WL, Trauner DA, Merritt TA, Singh M. Glutaric aciduria type 2. J Pediatr
1980;96:1020-6.
Dusheiko G, Kew MC, Joffre BI, Lewin JR, Mantagos S, Tanaka K. Récurrent hypoglycemia
associated with glutaric aciduria type 2 in an adult. N Engl J Med 1979;301:1405-9.
Gregersen N, K0lvraa S, Mortensen PB, Rasmussen K. C6-Ci0 dicarboxylic aciduria: biochemical
considérations in relation to diagnosis of β-oxidation defects. Scand J Clin Lab lnvest
1982;42:15-27.
Lindstedt S, Norberg K, Steen G, Wahl E. Structure of some aliphatic dicarboxylic acids found
in the urine of an infant with congénital lactic acidosis. Clin Chem 1976;22:1330-8.
Gregersen N, Rosleff F, K0lvraa S, Holboth S, Rasmussen K, Lauritzen R. Non ketotic C6-Cio
dicarboxylic aciduria: biochemical investigations of two cases. Clin Chim Acta 1980;102:
179-80.
Naylor EW, Mosovich LL, Guthrie R, Evans JE, Tieckelmann H. Intermittent non ketotic dicarboxylic aciduria in two siblings with hypoglycemia: an apparent defect in beta-oxidation of fatty
acids. J lnherited Metab Dis 1980;3:19-24.
Truscott RJW, Hick L, Pullin C, et al. Dicarboxylic aciduria; the response to fasting. Clin Chim
Acta 1979;94:31-9.
Tanaka K, Mantagos S, Gerel M, Seashore MR, Billings BA, Baretz BH. New defect in fatty
acid metabolism with hypoglycaemia and organic aciduria. Lancet 1977;2:986-7.
Chapoy P, Angelini S, Cederbaum S. Déficit systémique en carnitine. Place dans le syndrome
de Reye. Nouv Presse Méd (Paris) 1981;10:499-502.
Glasgow AM, Eng G, Engel AG. Systemic carnitine deficiency simulating récurrent Reye syndrome. J Pediatr 1980;96:889-91.
Karpati G, Carpenter S, Engel AG, et al. The syndrome of systemic carnitine deficiency: clinical,
morphologie, biochemical and pathophysiologic features. Neurology <NY) 1975;25:16-24.
Rebouche CJ, Engel AG. In vitro analysis of hepatic carnitine biosynthesis in human systemic
carnitine deficiency. Clin Chim Acta 1980;106:295-300.
Di Mauro S, Di Mauro PM. Muscle carnitine palmityl transferase deficiency and myoglobinuria.
Science 1973;182:929-31.
Bougnères PF, Saudubray JM, Marsac C, Bernard O, Odièvre M, Girard J. Fasting hypoglycemia
resulting from hepatic carnitine palmitoyl transferase deficiency. J Pediatr 1981;98:742-6.
Hermier M, Carrier H, Berthillier G, Feit JP, Jeune M. Hypotonie et encéphalopathie convulsivante avec myopathie lipidique et déficit en palmityl-carnitine transferase (P.C.T.). Entité nouvelle? Pédiatrie 1979;34:503-18.
Baudon JJ, Fontaine JL, Larrègue M, Feldmann G, Laplane R. Acrodermatitis enteropathica.
Etude anatomo-clinique de deux cas familiaux traités par le sulfate de zinc. Arch Fr Pediatr
1978;35:63-73.
Moynahan EJ. Acrodermatitis enteropathica: a lethal inherited human zinc deficiency disorder.
Lancet 1974;2:399-400.
Coddon R, Freycon MT, Lauras B, Châtelain Ph, Freycon F. Une nouvelle observation de maladie de Menkes. Pédiatrie 1979;34:695-706.
Danks DM. Hereditary disorders of copper metabolism in Wilson's disease and Menkes' disease.
In: Stanbury JB, Wyngaarden JB, Fredrickson DS, Goldstein JL, Brown MS, eds. The metabolic basis of inherited disease. 5th éd. New York: McGraw-Hill, 1983:1251-68.
DISCUSSION
Dr. Schwartz: My concern is not related to acute diagnosis and management, which in
most tertiary care centers is sophisticated, but rather to the long-term management of patients. In the United States our problème corne from our inability to adequately define nutrients; specifically, foods are not well labeled. In the management, for example, of galactosemia and hereditary fructose intolérance, it is almost impossible to instruct the family to
234
INBORN ERRORS OF METABOUSM
buy foods that hâve a known fructose or galactose content; we certainly avoid ail foods
containing additives, even if it is never put on the label, hot dogs for example. Even for
the pure foods, it is very difficult to exactly define the fructose content of spécifie foods.
This is an area that requires further thought. I hâve no idea what goes on in Europe, but if
it is as complicated as it is in the United States, it must also be very difficult to adequately
manage thèse patients.
Dr. Vidailhet: We also hâve some problems. Certain products produced by the agroalimentary industry sometimes also contain toxic metabolites. Another important aspect of
the long-term management is the family's understanding of the disease mechanism itself.
Dr. Schwartz: Hâve you considered doing duplicate diet analysis in spécifie diseases?
When you hâve a child on a particular diet, you can feed the child an equal quantity of the
same food as put into a container, as well as what is refused; both can be analyzed. This
is a familiar technique used in metabolic balance studies.
I hâve not heard of anyone using it on an outpatient basis, but, theoretically, it could be
a means for obtaining a spécifie measure of what, for example, the total fructose is in the
diet of a child that is presumably on a fructose-free diet.
Dr. Vidailhet: No, we did not use that technique.
Dr. Stern: I think what you are describing is another way of measuring how much did I
offer him, but how much did he actually take?
Dr. Schwartz: There is another area that is particularly important for fructose intolérance.
That is how to treat a child when he gets an infection. Fortunately, in the United States we
can call up virtually any drug company day or night and find out exactly what the ingrédients are, but it poses significant problems because many of the liquid préparations do hâve
fructose or sucrose as a filler.
Dr. Vidailhet: We do not hâve any problem in France, because the drug composition is
always clearly indicated.
Dr. Stern: I do not think Dr. Schwartz was talking about the drug composition but rather
about the vehicle in which the oral préparation for the antibiotics for young infants is given.
This may hâve a large amount of fructose or sucrose, and that is not usually indicated on
the label.
Dr. Goyens: We should be very cautious, when comparing Menkes disease (MD) and
copper deficiency, not to assimilate them. MD is much more complex than a copper deficiency; the copper metabolism in those patients is totally abnormal. Evidence can therefore
be found in the différent symptomatology of MD and copper deficiency, the inefficiency of
parenteral copper supplementation in MD and, probably more important, the abnormal handling of copper by cultured fibroblasts of MD patients. In fact, thèse fibroblasts hâve consistently elevated copper concentration compared to normal fibroblasts (1).
Secondly, you mentioned zinc, copper, iron, and manganèse deficiency in treated PKU
patients. There is, however, also a sélénium story in treated PKU patients that illustrâtes
very clearly the problems encountered with synthetic exclusion diets. Ingrid Lombeck (2)
in West Germany recently documented sélénium deficiency in thèse patients; we had the
same findings in Brussels. The deficiency is due to the very low sélénium content of synthetic diets used in thèse patients. Récent work done in Finland (3) and elsewhere (4)
showed that sélénium supplementation with organic sélénium, selenium-enriched yeast, is
much more effective than classical supplementation with sodium selenite or selenomethionine, not only in terms of plasma levels but also in terms of selenium-dependent enzymatic
activities. However, yeasts are very rich in phenylalanine. As a conséquence, we are still
unable to efficiently supplément PKU patients with organic sélénium.
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235
Dr. Stem: Dr. Goyens, what effects are seen from low sélénium?
Dr. Goyens: Thèse PKU patients hâve very low plasma levels of sélénium and very low
erythrocytic glutathione-peroxidase activity. They did not présent with clinical symptoms,
but in biochemical terms, there are important abnormalities.
Dr. Stem: The glutathione-peroxidase, for which sélénium appears to be a co-enzyme,
has been demonstrated in fact as being missing in some newborns also because of sélénium
deficiency. This study was done by Nathan Rudolph in Brooklyn several years ago. Unfortunately, no one has paid too much attention to it but it may be a cause of red cell breakdown. Is there any évidence in some of thèse patients that they hâve abnormal hemolysis?
Dr. Goyens: I do not know about PKU patients, but the same hypothesis has been put
forward to explain the shortened half-life for red blood cells in kwashiorkor patients (5).
Dr. Bakken: I just want to make a couple of comments regarding PKU disease. This
disease was discovered by a Norwegian doctor, A. Fôlling, 50 years ago. It has been followed very closely in Norway. You asked how long the patients should follow the diets.
A study in older patients from 20 to 30 years, in which the disease was not detected and
who are mentally retarded, shows that the behavior of thèse patients is very much improved
by the diet. A second comment—at the Institute of Nutrition at the University of Oslo, a
spécial program for families with PKU children was established that provided them with
ail the information about the content of amino acids in différent foods and made it easier
for them to know what to give and what not give, especially in the âge bracket 12 to 18
years when one may be a little bit less strict as far as the diet is concerned. They hâve now
also started a program for other diseases such as MSUD.
Dr. Vidailhet: The treatment of MSUD disease is much more difficult in the teenage
period; it is frequently very difficult to obtain strict adhérence to the diet, although adhérence to it is very important in MSUD. I personally discontinue the treatment after 12 years,
in PKU.
Dr. Bakken: We do not do the same now, because we saw that some of thèse patients,
when 13 or 15 years old, perform poorly at school. We carried out a lot of psychological
tests and other investigations, and it is obvious that some of them are better when remaining
on the diet. We pediatricians hâve neglected the teenagers. They make up a very important
group, but it seems that they do not belong anywhere.
Dr. Stern: In the United States and Canada, and to some extent in Britain, the adolescent
population belongs to the pediatricians, and it is now fairly rigorous that children under 18,
at least as a minimum, are pédiatrie patients and not internai medicine patients. Nevertheless, the adolescent problem is enormous. It is difficult enough to get an adolescent who is
allergie to chocolaté to stop eating chocolaté at a party, but we hâve ail kinds of difficulties,
for example, with adolescent diabetics who do not want to take their insulin. When you
impose a very restricted diet in a peer pressure situation, it becomes an enormous social
undertaking, not just a phenomenon of prescribing the diet and asking to hâve it. I suspect
that one of the reasons for discontinuing the diet at 12 is to avoid having trouble with adolescents who did not want to follow the diets, but Dr. Bakken's information is very interesting. It is difficult to obtain évidence for the necessity of a long-term diet on the basis of
improvements of patients who hâve not been treated up until that point. There we are, in
fact, facing the same problem as when giving iodine supplementation in iodine déficient
cretinism. On the other hand, there is no good évidence for the initial discontinuation of
the diets at either 6 or 12 years. If PKU is serious for the brain in the newborn, I know of
no évidence that would suggest that it does not remain serious when the brain is getting
older. I always wondered about the rationale for the discontinuation of the diets. I suspect
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that what our Norwegian colleague is saying may very well turn out to be correct, that
détérioration may be far more subtle in terms of what happens but that there is so far no
good évidence for discontinuation of the diet at any âge.
Dr. Padilla Munoz: I hâve been fortunate to follow three families with PKU disease that
were diagnosed very early and were treated with low phenylalanine diets. Thèse infants
presented with severe neurological damage, with convulsive disorders and mental retardation. I hâve been lucky to follow some of thèse patients for more than 15 years. At the âge
of 7 or 10 years, some of thèse cases were completely off of the low phenylalanine diet
and did fairly well. They showed minimal brain dysfunction with slight motor disorder and
low memory. One of them is already 17 years of âge and présents with hypogonadism.
Could it be that some PKU patients, if they hâve been treated in the first 5 or 10 years,
may do better afterwards and that some metabolic adjustments occur enabling thèse patients
to do fairly well without any spécifie diet?
Dr. Vidailhet: When PKU patients are treated very early, they do not présent with mental
disturbances and the prognosis is very good, contrary to what happens in galactosemia.
When treatment is ineffective, we need to exclude tetrahydrobiopterin (BU,) deficiency,
which requires another treatment. The behavior of untreated PKU children does not improve when they get older, and they remain severely mentally retarded. However, in atypical PKU, when the levels of phenylalanine are not so high, maybe between 15 to 20 mg
per dl, and when the patient is on a normal protein diet, the intelligence quotient may be
better.
Dr. Frenk: It is tempting to point out that in advanced malnutrition, one can find sorts
of caricatures of several of thèse genetically determined metabolic disorders. Advanced
malnutrition, particularly of the kwashiorkor (KWK) type, may, metabolically speaking,
mimic many of thèse diseases. For instance, one of the particular characteristics of KWK
is a transient deficiency of phenylalanine hydroxylase leading to a transient deficiency of
tyrosine, which thus becomes an essential amino acid until recovery takes place (6). Since
thèse metabolic caricatures are unfortunately much more common than the genetically determined diseases, they provide a golden opportunity for investigation of the many still unknown features of the latter. Another example is the acrodermatitis enteropathica-like appearance of dermal and mucosal lésions in many KWK patients (7). We do not know much
about minerai transport mechanisms in advanced malnutrition. Other examples of réversible
biochemical and clinical features, similar to those of some genetically determined diseases,
may be found (8) in many severe nutritional disorders.
Dr. Goyens: I cannot agrée entirely with Dr. Frenk's comment. It is true that some
symptoms and biochemical abnormalities observed in severe protein energy malnutrition
sometimes mimic very well those observed in some inborn errors of metabolism. However,
we should be very cautious. Indeed the term protein energy malnutrition (PEM) seems to
imply a primary problem with dietary protein and energy, but our knowledge of the pathophysiology of PEM in différent parts of the world is still far from conclusive. For example,
as far as zinc is concerned, I can hardly imagine how Golden's observations in Jamaica,
and ours in Central Africa (9), could help expiai η the pathophysiological mechanisms of
acrodermatitis enteropathica; it is rather the contrary!
Dr. Maggioni: From a practical point of view, could you give us some data about the
frequency of thèse metabolic diseases that require dietetic treatment, at least in France?
Dr. Vidailhet: The most frequently encountered is PKU; its frequency (1 in 16,000) is
well known thanks to the systematic neonatal screening. Urea cycle disorders are unfrequently seen, mostly OCT deficiency and citrullinemia. Contrary to our colleagues in the
United States we very seldom see cases of arginino succinic aciduria. Homocystinuria is
INBORN ERRORS OF
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237
very rare in France. Galactosemia is diagnosed in 1 in 50,000 neonates, MSUD 1 in
300,000.
Dr. Schwartz: I would like to comment on that last issue because I hâve been impressed
over the last 10 to 15 years that at least in the diagnosis of the urea cycle disorders, which
are often fatal, some progress has been made. This is because our junior housestaff hâve
been tuned into considering thèse defects and are making the diagnosis on the first or second day of life in infants who previously died and in whom we could not make the biochemical diagnosis.
Dr. Vidailhet: I agrée with your comment concerning the apparent frequency of inborn
errors of metabolism. The more we know about thèse diseases, the more fréquent they become, particularly in the neonatal period. One should think of metabolic disorder any time
the clinical picture suggests sepsis, which can easily be confused with metabolic disorders.
However, we need to be very careful, because sepsis may also occur in a child with an
inborn error of metabolism. The diagnosis of metabolic diseases can also be retarded when
the child has had a transfusion. In galactosemia, if the enzymatic assay is done after a transfusion, it may be quite normal.
Dr. Marini: I agrée that we are now more oriented toward thèse diagnoses, but there is
still a major problem with the very small preterm babies. When we see a full-term baby
mimicking a respiratory distress syndrome (RSD)—urea cycle disorders mimic RSD rather
than sepsis because they start with hyperventilation—after a few minutes, when you get the
answer from the laboratory that blood ammonia is very high, it is not difficult to hâve a
diagnosis, but it is not so easy with preterm infants. We do not really know the incidence
of the disease in the very low birth weight infant. Also confusing is that in cases of propionic acidemia, they often hâve a very high tendency to hemorrhage; very small babies with
propionic acidemia could be diagnosed as having intraventricular hemorrhage.
Dr. Vidailhet: We hâve to think about propionic acidemia when a metabolic acidosis
cannot be corrected with usual quantities of bicarbonate. As far as prématuré babies are
concerned, you are right: Hyperammonemia may be due to an inherited metabolic disorder,
or may be temporary, especially in children who had difficulties at birth, such as asphyxia
and so on.
Dr. Schwartz: I am concerned about the recommendation to use sodium benzoate in the
treatment of severe hyperammonemia. As far as I know, it is expérimental. It has significant risks associated with it, and I do not think it should be presented as a clear form of
therapy. I would like to see it presented as a question that needs further analysis.
Dr. Vidailhet: The emergency treatment with sodium benzoate, in cases of OCT deficiency, is very efficient. We use it. There may sometimes be a problem with unconjugated
bilirubin.
Dr. Stern: Sodium benzoate is a powerful displacer of bilirubin from albumin; in fact,
in the laboratory, it is the most potent one known. Caffeine sodium benzoate, which used
to be used for that purpose experimentally, gets its effect from the sodium benzoate and
not from the caffeine. That could be a problem only in a newbom with high bilirubin. Beyond the newborn period, I imagine you could use it without any difficulty.
Regarding PKU pregnant girls, in our department we hâve been working with monkeys
producing PKU and looking at monkey offspring. There is no question that they are badly
retarded in terms of performance and so on. People who hâve dealt with pregnant PKU
patients hâve, however, found a great deal of difficulty in controlling the diet to get an
adéquate protein intake during pregnancy and yet avoiding the outcomes. Some of them are
so discouraged that they simply suggest that thèse girls do not get pregnant at ail. Could
you comment on this phenomenon?
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Dr. Vidailhet: It is a very important problem now that more and more of our patients
become teenagers. I stop the diet in boys, but maintain it partly for girls. I maintain a small
quantity of spécial dietetic products. We now use Maxamaid XP, which is better in terms
of palatability and is better accepted.
We are not so strict anymore about the blood levels of phenylalanine after the âge of 12,
but in the girls we maintain part of the protein intake in the form of a spécial product that
is totally deprived of phenylalanine. It is very difficult to say to a teenage girl that she will
never hâve children. Another thing is that the diet of pregnant PKU patients needs to be
adjusted and again strictly controlled before conception and not 2 or 3 weeks later.
Dr. Stern: The question 10 years ago was considered to be quite important in neonatal
units regarding transient élévation· of tyrosine in small prématuré infants, which could be
reversed with vitamin C and with folie acid, and there were papers showing that if this was
not done, the children would not develop mentally as well as others. It was clearly related
to the amount of protein that was given in the diet. Would you comment about whether
this is still a real problem?
Dr. Vidailhet: High tyrosine levels were observed when the protein intake was much
more important, 4 to 5 g/kg/day. Now that the protein intake is lower, between 2.5 and
3.4 we do not observe high tyrosine levels anymore.
Dr. Stern: Dr. Scriver and I found that below 3 g of protein/kg/day you rarely got into
trouble, but if you did, ail you had to do was to give about 50 mg of vitamin C, which in
most infants would induce the enzyme System very quickly, even in very small prématurés.
Dr. Râihâ: It turns out that transient hypertyrosinemia in preterm infants is not really a
problem of vitamin C because this acts on the second enzyme in the tyrosine oxidation
pathway, on parahydroxyphenylpyruvate oxidase. The activity of that enzyme is normal in
preterm infants. The problem is with tyrosine aminotransferase, whose activity is not so
much affected by vitamin C. I do not really know if we can prevent that by just giving
vitamin C.
Dr. Stern: Can you induce it with anything?
Dr. Ràihâ: Yes, you can induce tyrosine aminotransferase by giving the substrate. It can
also be induced by corticosteroids.
Dr. Stern: Does folie acid work at that level?
Dr. Ràihà: I do not know that it does. Tyrosine aminotransferase is induced in vitro by
corticosteroids, by thyroxin, and by substrate.
Dr. Vidailhet: When we observe high tyrosine levels in prématuré babies, we see at the
same time elevated levels of parahydroxyphenylpyruvic, lactic, and acetic acids in urine.
This is in favor of parahydroxyphenylpyruvate oxidase deficiency much more than tyrosine
transaminase deficiency.
Dr. Vidyasagar: Until recently it has been legislated, at least in many states, that the
infants should hâve 24 hr of feeding before PKU screening, but recently in Illinois it has
been recommended that 24 hr would be sufficient with or without feeding because endogenous phenylalanine will show up. What is the expérience of other people?
Dr. Vidailhet: We wait until the third day of life before screening. The phenylalanine
level can go up, due to endogenous catabolism, but it is préférable not to do the screening
beforehand.
Dr. Stern: In other words, you think that if you do not feed the baby, it could not go up
in the first 24 hr but may take about 72 hr. That has also been our expérience. We used to
think it could take 5 days before we would get any élévation from endogenous breakdown
of protein.
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239
REFERENCES
1. Danks DM. Hereditary disorders of copper metabolism in Wilson's disease and Menkes' disease.
In: Stanburg JB, Wyngaarden JB, Fredrickson DS, Goldstein JL, Brown MS, eds. The metabolic
basis ofinherited disease. 5th éd. New York: McGraw-Hill, 1983:1251-68.
2. Lombeck I, Kasperek K, Harbisch HD, et al. The sélénium state of children. II. Sélénium content
of sérum, whole blood, hair and the activity of erythrocyte glutathione peroxidase in dietetically
treated patients with phenylketonuria and maple-syrup-urine disease. Eur J Pediatr 1978;128:21323.
3. Levander OA, Alfthan G, Arvilommi H, et al. Bioavailability of sélénium to Finnish men as assessed by plate let glutathione peroxidase activity and other blood parameters. Am J Clin Nutr
1983;37:887-97.
4. Tarino JZ. Evaluation of selected organic and inorganic sélénium compounds for sélénium dépendent glutathione peroxidase activity. Nutr Rep lnt 1986;33:299-306.
5. Vertongen F, Heyder-Bruckner C, Fondu P, Mandelbaum I. Oxydative hemolysis in protein malnutrition. Clin Chim Acta 1981;116:217-22.
6. Frenk S, Alejandre de Villarreal I, Benitez de Lopez S, Cuéllar A. Patrones plasmâticos de aminoâcidos libres en la desnutricion de tercer grado del lactante y del presescolar. Rev Méd lnst Mex
Seg Soc 1973;12:85-90.
7. Golden BE, Golden ΜΗΝ. Plasma zinc, rate of weight gain, and the energy cost of tissue déposition in children recovering from severe malnutrition on a cow's milk or soya protein based diet.
Am J Clin Nutr 1981;34:892-9.
8. Beck R, Durie PR, Hill JG, Levison H. Malnutrition: a cause of elevated sweat chloride concentration. Acta Paediatr Scand 1986;75:639-44.
9. Brasseur D, Goyens Ph, Vis HL. Some aspects of protein energy malnutrition in the highlands of
Central Africa. In: Eeckels RE, Ransome-Kuti O, Kroonenberg CC, eds. Child health in the tropics. Boston: Martinus-Nijhoff Publishers, 1985:167-78.