Polygenic risk for psychiatric disorder and singleness in patients with severe mental illness and controls

Abstract

We aimed to investigate whether the polygenic risk score (PRS) for schizophrenia influences time in couple relationships for patients with severe mental illness and controls. We combined the nationwide Danish registers with genetic information from dried neonatal blood spots. We included 2,599 individuals with schizophrenia, 1,446 with bipolar disorder, 20,315 with depression, and 6,963 controls. PRS for schizophrenia, depression, and bipolar disorder were estimated using data from the Psychiatric Genetics Consortium and analyzed both as a scale-predictor and as highest versus other deciles. The main outcome was number of days in couple relationships. Patients with schizophrenia had markedly fewer days/year in couple relationships: 64 (95% CI; 61-69) than patients with depression: 119 (95% CI; 117-121), bipolar disorder: 103 (95% CI 97-110), and controls: 136 (95% CI 133-139). PRS for schizophrenia was associated with fewer days in couple relationships in patients with schizophrenia (scale-PRS: IRR = 0.95 (0.93-0.97)) or depression (highest decile: IRR = 0.93 (0.87-0.98)). PRS for bipolar disorder (as scale) was also associated with fewer days in couple relationships in patients with depression (IRR = 0.99 (0.99-1.00)) or bipolar disorder (IRR = 0.96 (0.94-0.99)) and controls (IRR = 0.99 (0.97-1.00), and IRR = 0.89 (0.81-0.98) for the highest decile). Due to the number of statistical tests, however, it cannot be concluded definitely that some of these may not be spurious findings. In conclusion, our findings implicate high genetic loading for schizophrenia as a predisposing factor to singleness in patients with schizophrenia or depression, and genetic loading for bipolar disorder a similar predisposing factor in patients with depression, bipolar disorder or controls.

Keywords: Bipolar disorder; Depressive disorder; Gene-environment interaction; Schizophrenia; Single person.