CYP2D6 and Parkinson disease: The pooled analysis suggested that the CYP2D6*4 allele polymorphism was significantly associated with an increased risk of PD in all genetic models in the overall population: i) A vs. G allele (OR = 1.28, 95% CI = 1.14–1.43, P = 0.001); ii) AA vs. GG (OR = 1.43, 95% CI = 1.06–1.93, P = 0.018); iii) AG vs. GG (OR = 1.22, 95% CI = 1.06–1.40, P = 0.006); iv) AG+AA vs. GG (OR = 1.26, 95% CI = 1.10–1.44, P = 0.001); and v) AA vs. AG+GG (OR = 1.37, 95% CI = 1.02–1.83, P = 0.036).