Updated: 5/27/2020

Prader-Willi Syndrome

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Snapshot
  • A 2-year-old boy is brought to the pediatrician as a new patient. His mother reports that since he was young, he has fed very poorly, and has had decreased muscle tone compared to his siblings. Recently, he started displaying behavioral issues, such as hyperphagia. On physical exam, he is short, overweight, and has cryptorchidism. The pediatrician sends him for screening test for growth hormone deficiency, as well as to a geneticist for possible genetic testing.
Introduction
  • Overview
    • Prader-Willi syndrome is a disorder of imprinting associated with mutation or deletion of chromosome 15q11-13
      • this is an example of uniparental disomy
  • Epidemiology
    • incidence
      • 1 in 16,000-25,000
  • Pathogenesis
    • the maternal allele on chromosome 15q11.2-13 is normally methylated or silenced
    • mutation or deletion of the paternal allele then results in complete absence or defective gene expression, leading to Prader-Willi syndrome
  • Genetics
    • inheritance pattern
      • sporadic
    • mutations
      • 25% due to maternal uniparental disomy (2 copies of maternal chromosome 15)
      • mutation or deletion in paternal chromosome 15q11.2-13
        • genes identified include SNRPN, UBE3A, and necdin genes
  • Associated conditions
    • growth hormone deficiency
  • Prognosis
    • patients are typically able to function well into adulthood
Presentation
  • Symptoms
    • intellectual disability
    • hyperphagia
    • behavioral problems
  • Physical exam
    • neonate and infant
      • hypotonia
      • poor suck
      • failure to thrive
      • weak cry
      • genital hypoplasia
      • cryptorchidism
    • toddlers
      • delayed developmental milestones
    • children
      • obesity
      • small hands and feet
      • short stature
      • strabismus
      • scoliosis
Imaging
  • Radiograph
    • indication
      • assess for scoliosis
    • findings
      • curvature of spine
Studies
  • Serum labs
    • fasting levels of insulin-like growth factor 1 and insulin-like growth factor binding protein-3
      • screen for underlying growth hormone deficiency
      • confirm with provacative growth hormone stimulation est
  • Genetic testing          
    • chromosomal or microarray analysis
    • prenatal testing via chorionic villus sampling or amniocentesis
Differential
  • Angelman syndrome
    • key distinguishing factors
      • silenced maternal genomic material at chromosome 15q11.2-13
      • characterized by excessive laughter, hyperexcitability, and hand flapping
Treatment
  • Lifestyle
    • behavioral therapy
      • critical for conditioning child to normal eating habits and avoiding hyperphagia
    • diet and exercise
      • often requires coordination between home and school
    • calorie restriction
  • Medical
    • growth hormone
      • indications
        • growth failure
        • growth hormone deficiency
    • hormone-replacement therapy
      • indications
        • delayed puberty
  • Surgical
    • feeding tube
      • indication
        • growth failure in infancy
Complications
  • Hypopituitarism with deficiency in growth hormone
  • Scoliosis
  • Obstructive sleep apnea
  • Cor pulmonale

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