M56. ASSORTATIVE MATING IN SCHIZOPHRENIA AND BIPOLAR DISORDER: A NATIONWIDE COHORT STUDY EXPLORING THE CHARACTERISTICS OF INDIVIDUALS WHO HAVE CHILDREN BY PARTNERS WITH SCHIZOPHRENIA OR BIPOLAR DISORDER
Authors: Greve Aja , Uher Rudolf , Damm Als Thomas , Møllegaard Jepsen Jens Richardt , Lykke Mortensen Erik , Lou Gantriis Ditte , Ohland Jessica , Klee Burton Birgitte , Ellersgaard Ditte , Jerlang Cristiani Camilla , Spang Katrine , Hemager Nicoline , Plessen Kerstin , Thorup Anne , Bliksted Vibeke , Nordentoft Merete , Mors Ole 
Published: May 2020

Abstract

Background
Assortative mating is common in patients with mental disorders, both for specific disorders and across the spectrum of mental disorders. Assortative mating may play a key role in mental disorders because the person with the close relation to an individual with a mental disorder is also likely to have mental disorders, poorer cognitive abilities or lower social functioning, which may further intensify problems for both partners and their offspring. When one parent is ill, the care for the child will often depend on the other parent. Thus, assortative mating will most likely contribute to outcomes in the offspring. Therefore, the objective of this study was to investigate possible diagnoses of a mental illness, cognitive ability and social functioning in individuals who have biological children by partners with schizophrenia or bipolar disorder. Further, we also aimed to explore differences in polygenic risk scores derived from genome-wide association studies for schizophrenia, bipolar disorder, and depression.

Methods
This study was based on data from The Danish High Risk and Resilience Study - VIA7, a population-based cohort study conducted in Denmark between 2013 and 2016. Subjects were identified through the Danish Civil registration System and the Danish Psychiatric Central Research register. The VIA7 cohort consists of 522 children aged 7 years with parents diagnosed with schizophrenia or bipolar disorder in the Danish registries (index parents) and their partners (non-index parents). This study focuses on the non-index parents (N = 492) without schizophrenia or bipolar disorder in the Danish registries. All participants were interviewed with a diagnostic interview (SCAN 2.0). Main outcomes were intelligence, processing speed, verbal working memory, and social functioning. A linear mixed effect model was applied for each of the outcomes, including parent status (index parent or non-index parent), group (schizophrenia, bipolar disorder, and control), and interaction between parent status and group.

Results
Non-index parents having children by a partner with schizophrenia or bipolar disorder more often fulfilled the criteria for a mental disorder compared to non-index parents in the control group. Non-index parents having children by a partner with schizophrenia or bipolar disorder had lower levels of social functioning compared to non-index parents in the control group and performed poorer on intelligence and processing speed.

Discussion
Individuals who have children by partners with schizophrenia or bipolar disorder are more likely to have a mental disorder and to have lower levels of cognitive and social functioning compared to individuals who have children by partners without schizophrenia or bipolar disorder. Assortative mating may have important implications for our understanding of the familial transmission of these disorders. The findings presented in this study should be considered in future genetic research in psychiatry, specifically in the investigation of potential risk factors for children with a parent with schizophrenia or bipolar disorder.