The methylation levels of the parkin gene promoters were analyzed in samples from PD patients heterozygous for parkin mutations, PD patients without parkin mutations, and normal controls, however, no significant difference was observed among the three groups, indicating that parkin promoter methylation alone is unlikely to impact the pathogenesis and development of PD (Cai et al., 2011). This evidence concerns the gene PRKN and Parkinson disease.