A Systematic Review of the Familial Co-Aggregation of Schizophrenia With Non-Psychotic Disorders

Schizophrenia is a highly heritable mental health condition, likely due to a combination of genetic and environmental factors. Given that genes appear to predispose offspring to vulnerabilities or endophenotypes rather than to the disorder itself, and that environmental risk-factors tend to be shared across psychopathologies, we may expect other non-psychotic conditions to likewise aggregate with schizophrenia in families. This article reviews studies on familial co-aggregation of schizophrenia with other disorders, published over the past two decades. Twenty-two studies met inclusion criteria. Although many early family and cohort studies lacked statistical power due to small sample sizes, the overriding pattern is one in favor of familial co-aggregation of schizophrenia with a broad range of psychiatric conditions, including affective, anxiety, substance use, and childhood-onset disorders, which has been confirmed in recent population-based studies. Several causal hypotheses are proposed to explain these associations, which should be directly tested in future studies. These results suggest that family-based social work interventions for schizophrenia may benefit from an added emphasis on prevention and treatment of common mental health conditions among family members.