*   Department of Gynecology, Félix Guyon'Hospital, 97400 Saint-Denis, Ile de la Réunion, France;
**  Gynecologist, Moufia'street, 97400 Saint-Denis, Ile de la Réunion, France;
*** Department of Neonatology, Félix Guyon'Hospital, 97400, Saint-Denis, Ile de la Réunion, France.

Definition

Prader-Willi syndrome is characterized by pre and postnatal muscular hypotonia, thus giving an appearance of severe brain damage. Prader-Willi syndrome consists of low birth weight and early feeding problems with infantile hypotonia (floppy baby). Severe obesity appears later, associated with hyperphagia (obsessive-compulsive behavior). Profound hypotonia can cause asphyxia.

The children suffered with this condition have developmental delay (mild to moderate mental retardation), short stature with hypogenitalism in males and hypogonadism. Short stature and mild facial dysmorphism are present (rounded face, low forehead, almond shaped eyes, squinting). Prader-Willi syndrome is a neuroendocrine disorder.

Case report

This is a 36-year-old woman (G4P3), referred to our antenatal unit at 33 weeks of pregnancy due to a polyhydramnios without intra-uterine growth restriction and premature uterine contractions. The previous ultrasound scans at 13 and 22 weeks were normal and so was the triple test. Family history was unremarkable. Our ultrasound examination at 35 weeks revealed:

• Polyhydramnios (amniotic fluid index was 32 cm);

• Cryptorchidy;

• Fetal hypokinesis

No other abnormalities were seen. An amniocentesis was performed for uterine decompression and karyotyping (the karyotype was normal, 46 XY). The patient delivered at 37th week by cesarean section. The baby was hypoxic with decreased respiratory movements and had problems with swallowing later. Physical examination and neurological examination found muscular hypotonia without other external abnormalities. The hypotonia had lasted during the first month of life with slow improvement. The baby required prolonged oxygen therapy.

Complementary examinations (cerebral transfontanellar sonography, CT, MRI and EEG) were normal. A muscular biopsy was done with normal histological results. Steinert dystrophia was eliminated by DNA analysis.

Molecular analysis using microsatellite polymorphisms showed that the fetus had maternal disomy for chromosome 15. Southern blot analysis revealed a typical Prader-Willi syndrome abnormal methylation profile. The Prader Willi was the final diagnosis.

Images 1, 2: 35th week of pregnancy. Image 1 - cryptorchidy of the fetus; Image 2 - the fetal bladder was almost constantly full during our examinations.

Images 3, 4: 35th week of pregnancy. Image 3 - 2D fetal profile - micrognathia and polyhydramnios; Image 4 - 3D fetal profile - micrognathia.

History

J.L. Down in his classical text "Mental affections of childhood and youth", described a case resembling the signs of Prader-Willi syndrome. Prader, Labhardt and Willi in 1956, described a condition with the characteristic feature of obesity, short stature, and developmental delay (Klinge et al, 2001). Prader and Willi reviewed the condition in 1961, expanded the phenotype and described the presence of hypotonia in infancy and the development of diabetes mellitus later in childhood. Devonec et al (1998) described the first antenatal description of Prader-Willi syndrome (short long bones, cryptorchidy, polyhydramnios, akinesia).

Incidence

Incidence of Prader-Willi syndrome varies in published studies from 0.2 to 1:10,000 live births.

Etiology

The gene locus responsible for this condition is localized at chromosome 15 (15q11-q13 region). Prader-Willi syndrome occurs when the baby failing to receive active genes from this specific section of the father’s chromosome 15 and there are three different ways how this can happen:

- Paternal deletion - about 70% of cases;
- Maternal uniparental disomy - about 25% of cases;
- Imprinting defect - about 5% of cases.

Sonographic findings

There are no specific signs, but the literature states short femoral length associated with low maternal serum alpha-fetoprotein level, polyhydramnios, IUGR, fetal akinesia, hypoplasia of external genitalia, and cryptorchidism associated with this condition. Cerebral anomalies can sometime be present including ventriculomegaly, abnormal Sylvian fissure, abnormal cortical development and partial agenesis of the corpus callosum.

Prognosis

The babies suffering from Prader-Willi syndrome have a lower intelligence, with delayed attainment of developmental milestones. Diabetes mellitus or cardiac failure can appear later in life. The affected persons often have an insatiable hunger with overeating. Delayed or absent development of pubertal changes can be present.

References