ITGB4 and bipolar disorder: Cells transfected with both variants had increased proliferation at both 24 and 48 h (p = 0.013 and p = 0.05 respectively) compared to those with wild-type ITGB4. Taken together, these results suggest that rare variants in ITGB4 which affect function may contribute to the aetiology of schizophrenia and bipolar disorder.