A 2-year-old boy exhibits severe hypotonia, feeding difficulties in infancy, and early onset hyperphagia leading to obesity. Genetic testing reveals a deletion on the long arm of chromosome 15. Which genetic mechanism accurately describes this syndrome?

• A Deletion of the maternal chromosome 15
• B Uniparental disomy of chromosome 15 from the father
• C Deletion of the paternal chromosome 15 ✓
• D Trinucleotide repeat expansion on chromosome 15

Explanation

Prader-Willi syndrome is caused by the loss of function of genes on the paternally derived chromosome 15, either through a deletion or maternal uniparental disomy. The paternal genes in this region are imprinted and only expressed from the paternal allele. A maternal deletion causes Angelman syndrome instead. The progression from infantile hypotonia to childhood hyperphagia and obesity is the hallmark of Prader-Willi.

Reference: Nelson Textbook of Pediatrics, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.