Prader Willi Syndrome

on 6.6.05 with 0 comments



  • A disorder of chromosome 15
  • Prevalence: 1:12,000- 15,000 (both sexes, all races)

Major characteristics: hypotonia, hypogonadism, hyperphagia, cognitive impairment, difficult behaviors

Major medical concern: morbid obesity

The genetic cause is loss of yet unidentified genes normally contributed
by the father. Occurs from three main genetic errors: Approximately 70%
of cases have a non-inherited deletion in the paternally contributed
chromosome 15; approximately 25% have maternal uniparental disomy
(UPD)—two maternal 15s and no paternal chromosome 15; and 2–5 %
have an error in the "imprinting" process that renders the paternal
contribution nonfunctional.

Diagnostic testing: Individuals who have a number of the clinical
findings should be referred for genetic testing. DNA methylation
analysis confirms diagnosis of PWS. FISH and DNA techniques can identify
the specific genetic cause and associated recurrence risk. (See ASHG/ACMG
Report, Am J Hum Genet 58: 1085, 1996.) Patients who had negative
or inconclusive tests with older techniques should be retested.



Major Clinical Features:

Neonatal and infantile central hypotonia, improving with age

Feeding problems and poor weight gain in infancy
Excessive or rapid weight gain between 1 and 6 years of age; central obesity in the absence of intervention

Distinctive facial features—dolichocephaly in infants, narrow face/bifrontal diameter, almond-shaped eyes, small-appearing mouth with thin upper lip and down-turned corners of mouth

Hypogonadism—genital hypoplasia, including undescended testes
and small penis in males; delayed or incomplete gonadal maturation
and delayed pubertal signs after age 16, including scant or no
menses in women

Global developmental delay before age 6; mild to moderate mental
retardation or learning problems in older children

Hyperphagia/food foraging/obsession with food

Minor Features

  • Decreased fetal movement, infantile lethargy, weak cry
  • Characteristic behavior problems—temper tantrums, violent outbursts, obsessive/compulsive behavior; tendency to be argumentative, oppositional, rigid, manipulative, possessive, and stubborn; perseverating, stealing, lying
  • Sleep disturbance or sleep apnea
  • Short stature for genetic background by age 15
  • Hypopigmentation—fair skin and hair compared with family
  • Small hands and/or feet for height age
  • Narrow hands with straight ulnar border
  • Eye abnormalities (esotropia, myopia)
  • Thick, viscous saliva with crusting at corners of the mouth
  • Speech articulation defects
  • Skin picking


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Category: Pediatrics Notes

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