Download THE NORMAL METABOLISM OF PHENYLALANINE (pathways a

PHENYLKETONURIA (PKU) FACT SHEET
THE NORMAL METABOLISM OF PHENYLALANINE (pathways a and b) AND THE
ABNORMAL METABOLISM IN PHENYLKETONURIC SUBJECTS (pathway c)
HYDROXYPHENYLACETIC
ACID
Dietry
sources,
particularly
plant
proteins
BREAKDOWN
(c)
PHENYLALANINE
HYDROXYLASE
PHENYLALANINE*
(a)
TYROSINE
(c)
(b)
PHENYLACETIC
ACID*
BODY
PROTEINS
*Agents, thought to be responsible for mental retardation, which accumulate in phenylketonuric
subjects (PKU). These are broken down into ketone bodies which appear in the urine.
Other symptoms include skin lesions.
Test
Ferric chloride + urine of new born baby Green colour in the presence of ketone bodies.
Treatment
A strictly controlled phenylalanine low diet must be followed for life. No protein rich foods (e.g.
meat, eggs, pulses). No aspartame sweetner. As phenylalanine is itself an essential amino acid small
doses must be supplied. Other nutrients may need supplementing.
Frequency
1 in 10 000 in Caucasians of NW Europe
Causes
1. A single mutant recessive allele of the Phenylalanine Hydroxylase (PAH) gene. This results in
the inability to produce the enzyme.
Locus: Long arm of Chromosome 12.
2. Dietary excess of plant proteins which results in the exhaustion of a protein cofactor (pterin)
needed by the enzyme.
Evolution
Heterozygotes (carriers) are thought to be less susceptible to toxins produced by the moulds
Aspergillus and Penecillium. These grow on foods in damp wet climates (e.g. NW Europe).
Heterozygous women show lower spontaneous abortion rates.
14/05/2017