Williams syndrome — MRCPsych Paper A MCQ

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ModerateGeneticsWilliams syndromeMRCPsych Paper A

A 10-year-old child has mild intellectual disability, marked hypersociability, impaired visuospatial abilities and supravalvar aortic stenosis. Which underlying genetic abnormality is most likely?

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Correct answer: B — Microdeletion at chromosome 7q11.23

The combination of hypersociability, mild intellectual disability with visuospatial impairment, and supravalvar aortic stenosis is characteristic of Williams syndrome. It is caused by a hemizygous microdeletion at chromosome 7q11.23; deletion of the elastin gene within this region contributes to the cardiovascular phenotype. Trisomy 21 causes Down syndrome. A chromosome 4 CAG expansion causes Huntington disease, while an FMR1 CGG expansion causes fragile X syndrome. A paternal 15q11–q13 deletion causes Prader–Willi syndrome. Strictly, the microdeletion is the genetic abnormality rather than an inheritance pattern: most Williams syndrome cases arise de novo, although the deletion can subsequently be transmitted in an autosomal dominant manner.

Reference: NHS England National Genomics Education Programme, GeNotes Knowledge Hub: Williams syndrome, sections on Overview, Genomics, and Inheritance and genetic counselling; last reviewed 11 March 2025. https://www.genomicseducation.hee.nhs.uk/genotes/knowledge-hub/williams-syndrome/