'The clocks that time us'—circadian rhythms in neurodegenerative disorders

Sleep and circadian disruption are common in Alzheimer disease, Parkinson disease and Huntington diseaseSymptoms of circadian disruption range from subjective sleep complaints and alterations of sleep timing to severe disruptions in rest–activity cycles and sleep architectureBehavioural, physiological and molecular markers of circadian system function suggest progressive deterioration of circadian rhythmicity as the disease progressesThe relationship between circadian dysfunction and neurodegenerative processes might be bidirectional: circadian dysfunction might exacerbate the disease processesBehavioural or pharmaceutical interventions that target sleep–wake cycles might reverse circadian disruption