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22q11.2 deletion syndrome — MRCPsych Paper A MCQ

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ModerateGenetics22q11.2 deletion syndromeMRCPsych Paper A

A 19-year-old man with schizophrenia has a submucous cleft palate and underwent surgical repair of tetralogy of Fallot in infancy. There is no known family history of similar problems. Which genetic mechanism and inheritance description best fits this presentation?

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Correct answer: A — A 22q11.2 microdeletion, usually arising de novo but transmitted in an autosomal dominant pattern

The combination of a conotruncal cardiac defect, palatal abnormality and schizophrenia strongly indicates 22q11.2 deletion syndrome. It results from a heterozygous chromosomal microdeletion. Most cases arise de novo, explaining the absent family history, but an affected person has a 50% chance of transmitting the deletion to each child, so familial transmission is autosomal dominant. COMT lies within the commonly deleted region, but biallelic COMT deletion is not the cause of this syndrome. An HTT CAG expansion causes Huntington disease, which presents predominantly with progressive movement, cognitive and psychiatric features rather than congenital cardiac and palatal anomalies. Mitochondrial disorders and FMR1 premutations also do not produce this characteristic phenotype.

Reference: NHS England Genomics Education Programme, GeNotes Knowledge Hub: 22q11.2 deletion syndrome, last reviewed 2026. https://www.genomicseducation.hee.nhs.uk/genotes/knowledge-hub/22q11-2-deletion-syndrome/