The overall incidence of recurrent depressive disorders among patients with and without IFN-α-induced depression was 56.8 (95% confidence interval (CI), 42.4–76.1) and 4.1 (95% CI, 2.9–5.8) cases, respectively, per 100 000 person-years, P<0.001. This evidence concerns the gene IFNA1 and depressive disorder.