CLOCK and Parkinson disease: Blunted melatonin secretion profiles have been observed in PD and linked to clinically significant excessive daytime sleepiness (EDS) (Videnovic et al., 2014b), elevated serum cortisol, reduced melatonin, altered expression of the clock gene Bmal1, and disrupted nocturnal sleep continuity since the early disease stages (Breen et al., 2014).