COMT and major depressive disorder: In addition, while assaying the contribution of the aforementioned SNPs, COMT haplotypes and clinical variables in risk of depression in PD patients using a stepwise multivariate regression analysis, we found only the motor disability (UPDRS part III scores) and COMT rs6267 T allele contribute to the risk of depression in PD (Beta = 0.006, P < 0.01 for UPDRS part III scores; Beta = −0.338, P < 0.01 for rs6267 T allele, adjusted R2 = 0.067 and P = 0.01; Supplementary Table 3).