There are a large number of dopaminergic neurons in the SN of PD patients, which may affect the results; Secondly, the use of levodopa can reverse the hypomethylation status of SNCA gene introns, so methylation studies of PD patients who have been treated with levodopa may underestimate the methylation level of PD patients themselves.[17] Moreover, many current studies on methylation use bisulfite transformation sequencing or chip detection, which can not effectively identify 5mC and 5hmC, and may mistake 5hmC status for 5mC. Here, SNCA is linked to Parkinson disease.