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Jump to Key Points Individuals with psychiatric illness are more likely to partner with someone who has the same disorder or related condition, which may contribute to the prevalence and heritability of the disorders over generations, new research suggested.
A large population-based cohort study of couples and their offspring showed significant parental correlations for psychiatric disorders overall and for several individual psychiatric disorders. The trend was highest for schizophrenia, but associations were also found among partners with other conditions, including attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorder (ASD), and substance use disorder (SUD).
Partner similarity, also called nonrandom pairing or nonrandom mating, was associated with a nearly 2% increase in prevalence and a 12.5% increase in family-based heritability of any psychiatric disorder.
“When sustained over generations, nonrandom mating raises the baseline genetic vulnerability in the population, effectively increasing the overall prevalence of psychiatric conditions,” lead investigator Saeid Rasekhi Dehkordi, PhD, Copenhagen University Hospital and University of Copenhagen, Copenhagen, Denmark, and colleagues wrote.
- Psychiatric illness shows nonrandom partner similarity across couples.
- Strongest same-disorder correlation: schizophrenia r=0.38; ADHD/ASD r=0.35.
- SUD and generalized anxiety also showed partner correlations; GAD weakest r=0.11.
- Nonrandom mating estimated ↑ any psychiatric disorder prevalence by 1.8%.
- Nonrandom mating estimated ↑ family-based heritability by 12.5%.
The findings were published online on September 9 in JAMA Psychiatry.
Raises Genetic Vulnerability?
Nonrandom pairing has been well documented in other areas, such as height, weight, and socioeconomic status. Partner similarity has also been reported among individuals with cardiovascular disease and type 2 diabetes.
While prior research has also shown a trend toward nonrandom pairing among individuals with psychiatric illness, large, population-based cohort studies that control for psychiatric comorbidity were lacking.
To fill that gap, investigators assessed Danish registry data for more than 4.2 million residents (51.9% men; mean age, 26 years) born between 1969 and 2017 and identified 549,541 parental couples and 822,209 offspring.
Researchers calculated parental correlations for somatic conditions and for 10 major psychiatric disorders in 513,259 mother-father-offspring trios.
Separately, to estimate the effect on prevalence and heritability, they compared data from a subset of actual couples and their children with a computer-simulated version of the same group in which parents were randomly paired. Simulated partners were matched by age and birthplace.
Results showed strong parental correlations for psychiatric disorders overall among actual couples compared with the computer-generated cohort (Pearson correlation coefficient [r], 0.28; standard error, 0.003). The strongest within-disorder association was found for schizophrenia (r, 0.38), followed by ADHD (r, 0.35), ASD (r, 0.35), and SUD (r, 0.29; P < .001 for all).
The lowest within-disorder correlation was for generalized anxiety disorder (r, 0.11). Cross-disorder correlations ranged from a low of 0.01 to a high of 0.26 (for men with SUD and women with ADHD).
Weaker correlations were shown for somatic disorders, ranging from 0.03 to 0.14, which investigators attributed almost entirely to comorbid psychiatric disorders.
There was also an estimated 1.8% increase in the prevalence of any psychiatric disorder with nonrandom vs random mating in the empirical approach models and an estimated 12.5% increase in parent-offspring heritability.
‘Empirical Consequences’
The findings fit with previous research, Chun Chieh Fan, MD, PhD, co-director of the Center for Population Neuroscience and Genetics at the Laureate Institute for Brain Research in Tulsa, Oklahoma, told Medscape Medical News.
Although Fan was not involved with the current work, he led research published in 2025 that included some of the current investigators.
That study examined spousal correlations for nine psychiatric disorders in 5 million spousal pairs in Taiwan compared with data from Danish (571,534 pairs) and Swedish (707,263 pairs) national registries. Researchers noted that spousal correlations for most psychiatric disorders varied little by country or generation.
Fan said he was interested in assessing cultural differences in his study, whereas the current study investigators focused on “empirical consequences,” such as how the findings might affect a population’s dynamics. Still, he noted that both studies found similar correlation patterns with psychiatric disorders.
Based on the multiple countries included in the studies, it’s at least plausible that the findings might be generalizable to other populations, Fan noted. “It makes sense, but at the moment we just don’t know because of the need for more data, especially in the US,” he said.
Fan added that although both studies focus on population-level findings, one takeaway for clinicians is the importance of asking about family dynamics.
“If patients have a tendency to marry individuals who also have a psychiatric disorder, this sort of ‘co-dependency’ may require clinician awareness,” as well as considering whether to also refer the spouse for possible treatment, he said.
The study was funded by the National Institutes of Health and by the European Union’s Horizon 2020 research and innovation program. The investigators and Fan reported no relevant financial relationships.
