Our results showed that the RBDQ-HK, ESS, and PSQI scores completed by the PD patients (n = 264) were inversely associated with the expression levels of all five clock genes (r = −0.344∼−0.789, P < 0.01) and plasma melatonin (r = −0.509∼−0.753, P < 0.01, Table 3). Here, CLOCK is linked to Parkinson disease.