OCD Familial Risk — MRCPsych Paper B MCQ

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ModerateAnxiety & Stress-Related DisordersOCD Familial RiskMRCPsych Paper B

A systematic review and meta-analysis compares first-degree relatives of people with definite obsessive-compulsive disorder with first-degree relatives of control probands. Approximately what is the pooled odds ratio for definite OCD among the relatives?

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Correct answer: A — About 7-fold

The correct answer is A. A recent systematic review and meta-analysis found that first-degree relatives of OCD probands had approximately sevenfold greater odds of definite OCD than relatives of control probands (pooled odds ratio 7.18, 95% CI 4.13–12.47). This demonstrates substantial familial aggregation but does not mean that OCD follows simple Mendelian inheritance or that every relative has a high absolute probability of illness. The 4–5-fold estimate in option E is the most plausible distractor: approximately 4.6-fold was reported for a broader outcome incorporating definite and subthreshold obsessive-compulsive phenotypes. Estimates of onefold or twofold materially underestimate the association, whereas fifteenfold exceeds the pooled estimate for definite OCD.

Reference: Blanco-Vieira T, Radua J, Marcelino L, et al. The genetic epidemiology of obsessive-compulsive disorder: a systematic review and meta-analysis. Translational Psychiatry. 2023;13:230. https://pubmed.ncbi.nlm.nih.gov/37380645/