Adoption studies in schizophrenia — MRCPsych Paper A MCQ

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ModerateGeneticsAdoption studies in schizophreniaMRCPsych Paper A

A researcher compares rates of schizophrenia in adults adopted away at birth whose biological parents had schizophrenia with rates in adoptees whose biological parents did not have schizophrenia. What is the principal methodological advantage of this design?

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Correct answer: D — Inherited liability is partly separated from postnatal rearing effects

Explanation lettering: E = shown as A · A = shown as B · B = shown as C · C = shown as E

D is correct. Adoption away at birth reduces the usual correlation between biological relatedness and the postnatal family environment. Comparing adoptees according to illness in their biological parents therefore allows inherited liability to be distinguished partly from rearing effects. The separation is incomplete because prenatal and perinatal exposures, selective placement and other gene–environment correlations may remain. Shared environmental influences are not completely eliminated because adoptees still experience adoptive-family and wider environmental effects. Adoption does not prevent assortative mating in the biological parents and cannot eliminate diagnostic or ascertainment bias. Schizophrenia is a complex, multifactorial disorder; an adoption study neither demonstrates Mendelian inheritance nor proves that a single gene causes it.

Reference: Kendler KS, Ohlsson H, Sundquist J, Sundquist K. A Genetic Risk Adoption Design for Psychiatric and Substance Use Disorders. JAMA Psychiatry. 2026;83(1):51–58. https://pubmed.ncbi.nlm.nih.gov/41296336/