Chromosomal abnormalities · USMLE Step 1

A child with severe hypotonia, obesity, hyperphagia, and small hands/feet likely has which chromosomal mechanism causing the disease?

  1. Maternal deletion on chromosome 15q
  2. Paternal deletion on chromosome 15q
  3. Uniparental disomy maternal
  4. Trisomy 15 mosaicism
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Correct answer: Paternal deletion on chromosome 15q

Prader-Willi syndrome results from loss of paternal genes on 15q, either via deletion or maternal uniparental disomy. Symptoms include obesity and hypotonia. Maternal deletions cause Angelman syndrome.

Difficulty: Medium Question 8 of 20

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