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Angelman syndrome — MRCPsych Paper A MCQ

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EasyGeneticsAngelman syndromeMRCPsych Paper A

A 6-year-old girl has severe developmental delay, seizures, ataxia and frequent episodes of inappropriate laughter. Genetic testing identifies an imprinting abnormality involving chromosome 15q11-q13. Which molecular abnormality most likely explains her presentation?

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Correct answer: B — Loss of maternally expressed UBE3A function at chromosome 15q11-q13

The correct answer is B. Severe developmental delay, seizures, ataxia and frequent laughter are characteristic of Angelman syndrome. In neurons, UBE3A at chromosome 15q11-q13 is principally expressed from the maternal allele; loss of this maternal function causes Angelman syndrome. Mechanisms include maternal deletion, paternal uniparental disomy, an imprinting defect or a pathogenic maternal UBE3A variant. Loss of paternally expressed genes in the same region causes Prader–Willi syndrome, making B the principal distractor. DMD variants cause Duchenne or Becker muscular dystrophy, while mitochondrial transmission and biallelic trinucleotide-repeat expansion do not explain this imprinting-associated phenotype.

Reference: North Thames Genomic Laboratory Hub. Service Pack, Version 12.2, section “Angelman Syndrome R47”, 2025. https://norththamesgenomics.nhs.uk/wp-content/uploads/2025/08/ServicePack_v12.2.pdf