Danish Cohort Links Parental Psychiatric Similarity to Prevalence and Heritability Estimates

A population-based cohort study in JAMA Psychiatry examined how similarity between parents in psychiatric and somatic diagnoses relates to psychiatric disorder prevalence and family-based heritability. Using linked Danish national registries covering 4,244,585 residents born between 1969 and 2017, researchers identified 549,541 parental couples and 822,209 offspring. They calculated parental diagnostic correlations and compared observed prevalence and heritability estimates with a simulated random-mating scenario.

Parental correlation for psychiatric disorders overall was 0.28 (SE, 0.003). Within-disorder correlations were highest for schizophrenia at 0.38 and lowest for anorexia at 0.11; cross-disorder correlations ranged from 0.01 to 0.26. Correlations for somatic illnesses were weaker, ranging from 0.03 to 0.14, and were almost entirely accounted for by comorbid psychiatric disorders. Simulations estimated that the observed nonrandom-mating pattern inflated prevalence of any psychiatric disorder by 1.8% and family-based heritability by 12.5% relative to random mating.

The findings are relevant to interpreting familial clustering of psychiatric disorders and family-based heritability estimates. However, parental similarity does not establish assortative mating as its sole cause; other mechanisms may also contribute. The prevalence and heritability differences are simulation-based rather than observed causal effects. Only the abstract was available for this update, limiting assessment of modeling assumptions and other methodological details.