Our results provide empirical evidence that schizophrenia, bipolar disorder and major depressive disorder have shared genetic etiology. Because some schizophrenia and bipolar disorder cohorts were collected in the same clinical environments, we investigated the possible impact of the non-independent collection of schizophrenia and bipolar disorder samples sets but found no significant change in the estimates related to this (Supplementary Table 2). The correlation between schizophrenia and ASD was significant but small (0.16, 0.06 s.e.; P = 0.0071). In general, our analyses suggested that, whereas common genetic variants contribute to both childhood-onset disorders (ASD and ADHD) and disorders usually diagnosed after childhood (schizophrenia, bipolar disorder and major depressive disorder), the sharing of common variants between these groups is modest.
