Certain genetic variants of clock genes, including BMAL1 rs900147, PER1 rs2253820 (Gu et al., 2015), CLOCK 3111T/C (Lou et al., 2018), and Tef rs738499 (Hua et al., 2012), have been linked to specific PD symptoms such as tremors, motor fluctuations, sleep disorders, and depression, respectively. Here, CLOCK is linked to sleep disorder.