CYP2E1 and Parkinson disease: The hypomethylation of the CYP2E1 gene in the brain allows stronger expression of CYP2E1 in response to a given stimulus, and it was indeed shown that exposure to TCE causes PD in particularly susceptible men [19,26,27] and nigrostriatal degeneration with the development of parkinsonian features in animal models [28,29].