A significant decrease or increase in the expression of knockin and knockout PARK2, respectively, in iPSCs by CRISPR/Cas9 technology revealed that the PARK2 mutation, related to catechol-O-methyltransferase (COMT), may make a difference in the initial process of Parkinson's disease; treatment with central COMT inhibitors may thus be useful [89]. The gene discussed is COMT; the disease is Parkinson disease.