Table 1.

Summary of circadian rhythm abnormalities in AD, PD, and HD.

	Circadian rhythm abnormalities	Reference
AD	Daytime somnolence, increased sleep latency, and night-time awakenings Delayed phase of temperature circadian rhythm Sundowning Reduction of night-time melatonin levels Abnormal circadian expression profile of clock genes Increased IV, reduced IS, and reduced RA of rest–activity circadian rhythm	(3) (55) (56) (57) (57, 58) (20, 59, 60, 67)
PD	Abnormal melatonin circadian rhythm (phase advance and decreased amplitude) Increased IV, reduced IS, and reduced RA of rest–activity circadian rhythm Reversal of circadian BP rhythm and loss of HR variability Abnormal temperature and cortisol circadian rhythm Abnormal peripheral clock genes circadian rhythm	(70–73) (74–76) (77, 78) (73, 80) (73, 81)
HD	Delayed phase of the rest–activity rhythm Abnormal melatonin circadian rhythm Sleep fragmentation with night-time awakenings and reduced sleep efficiency	(88) (89) (90, 91)

AD, Alzheimer’s disease; PD, Parkinson’s disease; HD, Huntington’s disease; IV, intra-daily variability; IS, inter-daily stability; RA, relative amplitude; BP, blood pressure; HR, heart rate.