Molecular Biology/Genetics USMLE Step 1 Practice Question
A 3-year-old boy presents with hyperphagia, rapid weight gain despite normal appetite regulation attempts, hypotonia, and small hands and feet. He has moderate developmental delay and no history of feeding difficulties in infancy. Vital signs show BP 95/60, HR 88, RR 22, Temp 37°C, SpO2 98%. Growth hormone and thyroid function tests are normal. Genetic testing reveals a deletion on chromosome 15 inherited from his father. Which mechanism best explains this disease presentation?
Answer choices
- ABalanced reciprocal translocation
- BExpansion of CGG trinucleotide repeats with methylation
- CDefect in maternally inherited mitochondrial DNA
- DDefect in paternally expressed genes due to genomic imprintingCorrect answer
- EMutation in a DNA mismatch repair gene
- FAutosomal dominant inheritance with reduced penetrance in the paternal lineage
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