Prader-Willi syndrome — MRCPsych Paper A MCQ

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EasyGeneticsPrader-Willi syndromeMRCPsych Paper A

A 9-year-old boy developed hyperphagia, obesity, short stature and learning difficulties after marked neonatal hypotonia and feeding problems. Which molecular genetic abnormality most likely underlies his condition?

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Correct answer: A — Absent expression of paternally expressed genes at 15q11-q13

The correct answer is A. Neonatal hypotonia and feeding difficulty followed in childhood by hyperphagia, obesity, short stature and learning difficulties is characteristic of Prader-Willi syndrome. It results from absent expression of paternally expressed genes in chromosome 15q11-q13, caused most commonly by a paternal deletion but also by maternal uniparental disomy or an imprinting defect. Absent maternal UBE3A expression causes Angelman syndrome, which typically features severe developmental impairment, minimal speech, ataxia and seizures. A CAG expansion suggests disorders such as Huntington disease; an MECP2 variant is associated with Rett syndrome; and mitochondrial deletions produce different multisystem phenotypes.

Reference: Shropshire Community Health NHS Trust. Guideline for Management of Prader-Willi Syndrome in Children and Young People, section 5.1 Genetics and sections 5.3–5.4 Clinical Manifestations/Diagnosis. 2025. https://www.shropscommunityhealth.nhs.uk/content/doclib/11499.pdf