This article is more than 5 years old. Information may no longer be current.

Research shows nonrandom mating across psychiatric disorders

Recent findings indicated nonrandom mating within specific psychiatric disorders and across the spectrum of psychiatric disorders.

“Psychiatric disorders are heritable, polygenic traits, which often share risk alleles and for which nonrandom mating has been suggested. However, despite the potential etiological implications, the scale of nonrandom mating within and across major psychiatric conditions remains unclear,” Ashley E. Nordsletten, PhD, of Karolinska Institutet, Stockholm, and colleagues wrote.

To assess the nature and extent of nonrandom mating within and across a broad range of psychiatric disorders, researchers used Swedish population registers to analyze a population-based cohort. Participants included individuals with attention-deficit/hyperactivity disorder, autism spectrum disorder, schizophrenia, bipolar disorder, major depression, generalized anxiety disorder, agoraphobia, social phobia, obsessive-compulsive disorder, anorexia, or substance abuse and their mates. Individuals with nonpsychiatric disorders, including Crohn’s disease, type 1 and type 2 diabetes, multiple sclerosis or rheumatoid arthritis, were included for comparison. Data corresponded with 707,263 unique case individuals.

Within each disorder, mates of both sexes were significantly correlated for diagnostic status, ranging from 0.11 to 0.48.

Cross-disorder correlations were also observed, ranging from 0.01 to 0.42, and were typically lower than within-disorder correlations.

A disorder in a case was typically associated with a 2-fold to 3-fold increase in a mate’s risk for having the same or an alternate condition, according to researchers. These risks were compounded in ADHD, ASD and schizophrenia, though small sample sizes may have affected this finding.

Odds for any diagnosis among mates of case probands significantly increased for males (OR = 2.24; 95% CI, 2.21-2.27; P < .001) and females (OR = 2.11; 95% CI, 2.08-2.14; P < .001).

The proportion of case probands with an affected mate increased linearly as the number of comorbidities in the proband increased.

These findings may help to solve three “puzzles” in psychiatric genetics, according to Robert Plomin, PhD, of King’s College London, and colleagues, including 1) why psychiatric disorders are highly heritable while they are associated with reduced fecundity; 2) why some psychiatric disorders are significantly more heritable than others; and 3) why there is such genetic comorbidity across psychiatric disorders.

“These findings are intriguing in relation to the first two puzzles about heritability of psychiatric disorders. The significance of assortative mating for polygenic traits, such as psychiatric disorders, is that it increases additive genetic variance generation after generation until equilibrium is reached,” Plomin and colleagues wrote in an accompanying editorial. “As a consequence, assortative mating increases the contribution of additive genetic variance (narrow heritability) for any trait on which it acts. This boost to heritability from assortative mating could help to explain why psychiatric disorders have such high heritability despite reduced fecundity.” – by Amanda Oldt

Disclosure: Nordsletten reports no relevant financial disclosures. Plomin reports directing the Twins Early Development Study, supported by program grant G0901245 (and previously G0500079) from the UK Medical Research Council, with additional support by grants HD044454 and HD059215 from the U.S. National Institutes of Health; and being supported by Medical Research Council Research Professorship award G19/2 and by European Research Council Advanced Investigator award 295366. Please see the full study for a list of all authors’ relevant financial disclosures.