Download Hypotonic infants and the Prader-Willi Syndrome

246 Jornal de Pediatria - Vol. 76, Nº3, 2000
0021-7557/00/76-03/246
Jornal de Pediatria
Copyright
© 2000 by Sociedade Brasileira de Pediatria
CASE REPORT
Hypotonic infants and the Prader-Willi Syndrome
Cintia Fridman,1 Fernando Kok,2 Célia P. Koiffmann3
Abstract
Objective: to describe 6 patients with less than 3 years of age that were diagnosed with Prader-Willi
syndrome (PWS) due to hypotonia, poor sucking, slight facial anomalies and minor abnormalities of hands
and feet. PWS is a neurobehavioural disorder characterized by two distinct phases; in the first, the neonate
presents variable degree of hypotonia, feeding problems with none or poor sucking; hypogonadism,
characteristic facial features with almond shaped eyes, narrow bifrontal diameter and down-turned corners
of the mouth. Neuropsichymotor development is delayed. Hypotonia is non progressive and tends to
improve between 8 and 11 months of age. The second phase then starts and is characterized by increasing
hyperphagia and obesity, among other features. Unfortunately, most PWS patients are diagnosed only after
obesity is installed.
Methods: Methylation, microsatellites analysis and karyotypic studies by traditional and in situ
hybridization techniques were done.
Results: A deletion of chromosome segment 15q11q13 was disclosed in 4 and maternal disomy in two
patients.
Conclusion: the diagnosis of PWS is generally established after the onset of obesity. So, we suggest
that the genetic analysis must be carried out in children with severe hypotonia of unknown cause, poor
sucking and some facial features of PWS (small hands and feet, hypogonadism, hypopigmentation, almond
eyes and narrow bifrontal diameter). This can allow the early diagnosis and avoid invasive exams necessary
for neuromuscular disorder diagnosis like muscle biopsy and electroneuromiography, wich frequently are
associated with inconclusives results.
J Pediatr (Rio J) 2000; 76(3): 246-50: Prader-Willi syndrome, hypotonia, genomic imprinting,
deletion 15q11q13, maternal UPD15, hypogonadism.
Introduction
Prader-Willi syndrome (PWS), a neurobehavioral
disorder which was first described in 19561, is currently one
of the most frequent syndromes with chromosomal
microdeletions, and the most common type of obesity of
genetic origin.2 In addition, PWS and the Angelman
syndrome (AS) (delay in neuropsychomotor development,
mental retardation, absence of speech, convulsions, and
happy disposition) were the first human diseases
acknowledged as being determined by the genomic
imprinting mechanism. 3 The incidence of PWS is
approximately 1/10,000 to 1/30,000 births4,5 and it is
usually sporadic, with few familial cases reported.6
Although many PWS clinical manifestations result from
hypothalamic deficiencies, no structural defect of the
hypothalamus has been found in postmortem exams.
1. MSc, Biology/Genetics. Genetic Counseling Unit, Biology Department IBUSP, São Paulo, Brazil.
2. Ph.D, Assistant Physician. Infant Neurology Service, Hospital das Clínicas
- FMUSP, São Paulo, Brazil.
3. Ph.D., Professor, Chief of the Genetic Counseling Unit, Biology Department
- IBUSP, São Paulo, Brazil.
246
Hypotonic infants and the Prader-Willi Syndrome - Fridman C et alii
Therefore, the deficiency seems to be functional, but its
nature remains unknown.2 During the past few years, the
genetic base of PWS has been extensively investigated;
still, the clinical diagnosis of this disorder is complex,
considering that some characteristics change according to
the age and can be present in other syndromes as well.
PWS can be defined as presenting two distinct
phases.4,7,8 The first is characterized by different levels of
hypotonia during the neonatal period and the early childhood
years (94%). Hypotonia is nonprogressive, and it starts to
improve on average between the age of 8 and 11 months.
Hypotonia is also characterized by hypothermia or
hyperthermia without any apparent cause, hypogenitalism
(95%), poor sucking (93%), small hands and feet and minor
facial anomalies. Another aspect observed is that these
children rarely vomit.
When hypotonia improves, and the child becomes more
alert, there is an increase in appetite and weight gain. The
onset of obesity may take place between the ages of 1 and
6, with an average at 2 years8,9 and it may be a marker to
signal the beginning of the second phase. This second phase
is characterized by a delay in neuropsychomotor
development (98%) - the child presents a delay in learning
how to sit, walk, and in speech acquisition. Other
characteristics that are present in this phase are hyperphagia,
obesity (94%), low stature (76%), small hands and feet
(83%), decreased physical activity, decreased sensitivity to
pain,8,10 hypopigmentation of hair, skin and retina, learning
impairment, and facial characteristics such as a narrow
forehead (75%), almond-shaped eyes (75%), and strabismus
(52%). Some children between 3 and 5 years of age may
develop personality problems, such as depression, irritation,
violence episodes, sudden mood changes, little interaction
with people, immaturity, and inappropriate social
behavior.11
PWS results from the absence of paternal genes that are
usually active in chromosomal segment 15q11-q13; the
maternal inherited alleles are usually inactive, due to the
genomic imprinting mechanism. These paternal genes may
be absent as a result of different mechanisms: 75% of the
PWS cases present paternal deletion of segment 15q11q13; 20-25% present maternal uniparental disomy
(inheritance of two maternal chromosomes 15);12,13
approximately 5% of the PWS cases present translocation
or other structural chromosomal anomaly involving
chromosome 15; around 1% of the patients (including all
the families with recurrence of PWS that have been studied
so far) do not present deletion or uniparental disomy, but
instead present a microdeletion in the imprinting controller
center, called imprinting center, located in segment 15q11q13.6,14,17
In this work, we describe the clinical characteristics and
the genetic diagnosis of six patients younger than 3 years of
age, emphasizing the importance of an early PWS diagnosis.
Jornal de Pediatria - Vol. 76, Nº3, 2000 247
Patients and Methods
Patients
The patients were referred to the Genetic Counseling
Service (IB-USP) with hypotonia, poor sucking and slight
anomalies on the face and extremities (Figure 1). Consent
for publication of the photographs was obtained from all
parents.
Genetic study
The diagnosis of PWS was established through analysis
of the exon 1 methylation pattern in the SNRPN gene,
located in the PWS and AS critical region, using the
Southern blot technique.18 The genetic mechanism was
determined through the analysis of the chromosome 15
microsatellite segregation standard, using the polymerase
chain reaction (PCR) technique,19 G-banding karyotype
and fluorescent in situ hybridization (FISH).
Results
The patients’ clinical characteristics are summarized in
Table 1. The karyotypic analysis was carried out in five out
of six patients, with results in all of them. Regarding
molecular results, all six patients presented a typical PWS
methylation pattern, confirming the clinical suspicion. The
analysis of microsatellites, along with FISH results, revealed
that, out of six patients with PWS, four presented deletion
of segment 15q11q13, and two presented maternal
uniparental disomy.
Discussion
The differential diagnosis of hypotonia in infants includes
neuromuscular diseases such as infant spinal amyotrophy
and congenital myopathies. For the diagnosis of these
diseases, the performance of electroneuromyography and
muscle biopsy is indicated. The performance and
interpretation of these invasive exams is sometimes difficult,
and they may lead to wrong diagnoses. In PWS, muscle
biopsy can reveal atrophy of type-II fibers, but this finding
is not specific.
The karyotype rarely defines a diagnosis of PWS or AS.
Currently, the most efficient method to diagnose these
diseases is a molecular test that determines the progenitorspecific methylation pattern in the PWS/AS region, using
Southern blot and hybridization with probes that are sensitive
to methylation of the SNRPN and PW71 loci.6,20-23 In
patients with suspicion of PWS, a normal methylation
pattern eliminates the possibility of PWS with 95% certainty.
Although the prevalence of PWS in children with
hypotonia is not known, the methylation test has to be
considered for the differential diagnosis, mainly among
infants presenting serious hypotonia of unknown cause.
Hypotonic infants and the Prader-Willi Syndrome - Fridman C et alii
248 Jornal de Pediatria - Vol. 76, Nº3, 2000
A
D
B
C
E
F
Figure 1 - Patients with Prader-Willi syndrome. a) Patient 6 - 2 years and 4 months old; b) Patient 3 - 1 year and 8 months old; c) Patient
2 - 10 months old; d) Patient 4 - 9 months old; e) Patient 1 - 9 months old; f) Patient 5 - 10 months old. See slim fingers in
b, c, e and f, strabismus in a, b, e and f, mouth bent downwards in a, c, and e
Gillessen-Kaesbach et al.11 tested 65 children between 0
and 12 months of age with idiopathic hypotonia and detected
29 PWS cases (45%). Those authors emphasize that although
this frequency is probably overestimated, due to an
investigation bias, the methylation test should be performed
in this group of patients, considering that it is non-invasive
and extremely effective to diagnose PWS.
The prenatal diagnosis through the study of the
methylation pattern should be considered in families with
rearrangements in chromosome 15, in women who already
had a child with the syndrome, and in patients with trisomy
of chromosome 15 on chorionic villus culture and a normal
chromosome count on amniocentesis,24 since it is known
that advanced maternal age is associated with cases of
uniparental disomy 15, due to its association with meiotic
errors.25 In our sample, we also observed that the mothers
were older in uniparental disomy cases.
The search for the genetic mechanism that causes PWS
is important for the genetic counseling of parents and
relatives. The risk for deletion and disomy is low, around
1%; the only high risk (50%) is associated with rare
occurrences of mutations and translocations in the imprinting
mechanism.
The early diagnosis of PWS is important because it
gives the parents the opportunity of providing adequate
diets and stimulating appropriate eating and exercise habits,
so as to reduce the problems related to obesity, e.g. diabetics,
hypertension, and respiratory problems, which are the main
causes of death among these individuals during adolescence.
In addition, children and teenagers with PWS present a
developmental delay in several fields, and an early diagnosis
prompts the parents to look for professional help (teachers,
pedagogues, physical therapists, and speech therapists).
During adolescence, the family may lose control over
the child’s diet, since teenagers seem to use their intelligence
and shrewdness to obtain food, becoming aggressive when
it is denied to them. These individuals may eat leftovers, pet
food, and some of them even eat dirt; some children may
develop “psychotic” behaviors. 11 Experience shows that
psychological support to the patient and to the parents and
Hypotonic infants and the Prader-Willi Syndrome - Fridman C et alii
Table 1 -
Jornal de Pediatria - Vol. 76, Nº3, 2000 249
Clinical characteristics and complementary exams of PWS carriers
Patient
1
2
3
4
5
6
Sex
F
M
M
F
F
M
Age (months)
9
10
20
9
10
28
Mother’s age (years)
45
22
28
30
20
48
Father’s age (years)
41
24
25
34
29
52
Fetal movements
0
Normal
Decreased
Normal
Normal
Decreased
Birth weight (g)
2110
2390
2680
3025
2440
1780
Length (cm)
42
47
48
51
45
36
Hypotonia
+
+
+
+
0
+
Poor sucking
+
+
+
+
+
-
Delay in neuropsychomotor
development
+
+
+
+
+
+
Weight
10<P<25%
10%
25<x<50%
50%
90<x<97%
<2.5%
Height
10<P<25%
0
2,5%
75%
75%
<2.5%
50%
25<P<50%
50<x<75%
75%
0
<2.5%
-
+
+
+
-
-
Cephalic perimeter
Hypertelorism
Almond-shaped eyes
+
+
+
0
+
0
Strabismus
+
+
-
+
+
+
Narrow forehead
+
+
+
-
+
+
Small hands and feet
+
+
0
+
+
+
Muscle biopsy
NP
type II FA
type II FA
NP
NP
type II FA
Electroneuromyography
NP
Normal
Myopathic
NP
NP
Myopathic
UPD*
Deletion
Deletion
Deletion
Deletion
UPD
Genetic mechanism
+ = presence of characteristic
- = absence of characteristic
0 = data not available
NP = not performed
type II FA = type II fiber atrophy
UPD = uniparental disomy
* = prenatal exam performed, showing chromosome 15 trisomy on chorionic villus sampling and normal complement on amniocentesis
brothers/sisters should begin during childhood and continue
throughout adulthood, when the major problem is weight
and behavior control, with the occurrence of irritation
periods, and sometimes of psychotic episodes.
Since in our setting the diagnosis of PWS is generally
established after the beginning of obesity, we suggest genetic
testing for this disease be requested in newborns and infants
presenting hypotonia, poor sucking, and some of the
phenotypic characteristics of PWS (small hands and feet,
signs of hypogonadism, hypopigmentation in relation to
relatives, almond-shaped eyes, narrow forehead). This may
help the establishment of an early diagnosis, decreasing the
need for more invasive diagnostic resources, sometimes of
difficult interpretation, such as electroneuromyography and
muscle biopsy.
Acknowledgment
This work was spondored by FAPESP (C.F.) and
PRONEX (C.P.K.).
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Correspondence:
Dra. Cintia Fridman
Unidade de Aconselhamento Genético, IBUSP
Caixa Postal 11461
CEP 05522-970 – São Paulo, SP, Brazil
E-mail: [email protected]