The genotype GG of ADORA1 rs2228079 (recessive model) was significantly more frequent in patients with OCD/OCB (OR 2.86, 95% CI: 1.14–7.21, p = 0.021) and depression (OR 2.94, 95% CI: 1.06–8.13, p = 0.032) than in patients without these co-morbidities. The gene discussed is ADORA1; the disease is major depressive disorder.