The expression of clock genes is altered in leukocytes from patients with Parkinson's disease (PD). However, the underlying mechanisms are unknown. To determine whether abnormal CpG methylation contributes to the dysregulated expression of these genes, the methylation status of the promoters of seven major human clock genes, PER1, PER2, CRY1, CRY2, Clock, NPAS2, and BMAL1, was examined using methylation-specific PCR (MSP) and sequencing in 206 PD patients and 181 healthy controls. This analysis revealed that most clock gene promoters were devoid of methylation. Methylation was only detectable in the CRY1 and NPAS2 promoters. Interestingly, the methylation frequency of the NPAS2 promoter was significantly decreased in PD patients. These results suggest that altered promoter methylation may contribute to the abnormal expression of clock genes in PD.
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