Psychiatric disorders are highly polygenic and show patterns of partner resemblance. Partner resemblance has direct population-level genetic implications if it is caused by assortative mating, but not if it is caused by convergence or social homogamy. Using genetics may help distinguish these different mechanisms. Here, we investigated whether partner resemblance for schizophrenia and bipolar disorder is influenced by assortative mating using polygenic risk scores (PRSs).

PRSs from The Danish High-Risk and Resilience Study—VIA 7 were compared between parents in three subsamples: population-based control parent pairs (N=198), parent pairs where at least one parent had schizophrenia (N=193), and parent pairs where at least one parent had bipolar disorder (N=115).

The PRS for schizophrenia was predictive of schizophrenia in the full sample and showed a significant correlation between parent pairs (r=0.121, p=0.0440), indicative of assortative mating. The PRS for bipolar disorder was also correlated between parent pairs (r=0.162, p=0.0067), but it was not predictive of bipolar disorder in the full sample, limiting the interpretation.

Our study provides genetic evidence for assortative mating for schizophrenia, with important implications for our understanding of the genetics of schizophrenia.

Sex differences in brain structure and neurodevelopment occur in non-clinical populations. We investigated whether sex had a similar effect on developmental domains amongst boys and girls with a familial risk of schizophrenia (FHR-SZ), bipolar disorder (FHR-BP), and controls.

Through Danish registries, we identified 522 7-year-old children (242 girls) with FHR-SZ, FHR-BP, and controls. We assessed their performance within the domains of neurocognition, motor function, language, social cognition, social behavior, psychopathology, and home environment.

FHR-SZ boys compared with FHR-SZ girls had a higher proportion of disruptive behavior and attention-deficit hyperactivity disorder (ADHD) and exhibited lower performance in manual dexterity, balance, and emotion recognition. No sex differences were found between boys and girls within FHR-BP group. Compared with controls, both FHR-SZ boys and FHR-SZ girls showed impaired processing speed and working memory, had lower levels of global functioning, and were more likely to live in an inadequate home environment. Compared with control boys, FHR-SZ boys showed impaired manual dexterity, social behavior, and social responsiveness, and had a higher proportion of ADHD and disruptive behavior disorder diagnoses. Stress and adjustment disorders were more common in FHR-BP boys compared with control boys. We found no differences between FHR-BP girls and control girls.

Impairment within neurodevelopmental domains associated within FHR-SZ boys v. FHR-SZ girls was most evident among boys, whereas no sex differences were found within the FHR-BP group (FHR-BP boys v. FHR-BP girls). FHR-SZ boys exhibited the highest proportion of early developmental impairments.

Neurocognitive and social cognitive impairments are central characteristics of schizophrenia and, to a lesser extent, of bipolar disorder. Birth cohorts and familial high risk studies have described cognitive impairments in subjects before onset of diagnosis as well as in children with increased genetic risk for development of the disorders.

To our knowledge, this is the first study to investigate the correlations between neurocogntion and social cognition in parents and offspring simultaneously and with the same methodology. We will divide the parents into subgroups (cognitive impairment and good cognitive functioning) and use these subgroups to describe correlations with their offspring. Identifying associations between parents and offspring can add important clues to risk factors for schizophrenia and bipolar disorder and, on the long-term, help the development of more effective and potentially preventive treatments.

This study is part of the Danish high risk and resilience study–VIA7. The VIA7 cohort consists of 522 children age 7 with zero, 1 or 2 parents diagnosed with schizophrenia or bipolar disorder and both of their biological parents. We assessed neurocognition and social cognition with a comprehensive test battery including: intelligence (RIST), executive functions (WAIS-IV, D-KEFS, CANTAB), verbal memory (TOMAL2), attention, emotion recognition, decision making and response control (CANTAB), theory of mind (animated triangles) and social perception (TASIT). Parental subgroups were based on the 95% CI of the controls (cognitive impairment < 95%CI and good cognitive functioning > 95% CI).

Data analysis is ongoing and results will be presented at the conference.

The authors have not supplied their declaration of competing interest.