CYP2D6 and Parkinson disease: Corroborating that the interplay of genetic and environmental risk factors increases the susceptibility to sporadic PD, a recent study found a significantly higher allele and genotype frequency of the CYP2D6*4 variant in 174 sporadic PD patients when compared to 200 controls [27] providing evidence on the hypothesis that a poor metabolizer status may increase the risk to develop PD especially in populations that are exposed to environmental toxins [27].