Epigenetic basis of circadian rhythms and sleep disorders

As our understanding of the genetic basis of circadian rhythms and sleep and of related disorders has evolved, interest in defining the corresponding role played by epigenetics in these normal and pathological processes has been increasing. Epigenetics – a field that is still in its infancy – is intimately linked with genetics. In essence, epigenetics refers to the study of how genetic information is packaged and selectively utilized in a context-dependent manner and in response to environmental stimuli. Gene transcription is one of the principal cellular functions subject to epigenetic control. As pluripotent stem cells differentiate, for example, the coordinated actions of distinct but interconnected layers of epigenetic mechanisms are responsible for silencing pluripotency genes and for activating tissue- and cell lineage-specific genes [1]. Epigenetic mechanisms can mediate gene expression changes that are permanent (as in the above example) as well as those that are more dynamic or even oscillating. Because of their critical functions, it is not surprising that epigenetic factors and mechanisms – and their dysfunction – have now been linked to the pathophysiology of nearly every major class of disease including, most prominently, cancer, metabolic, inflammatory, and nervous system disorders [2].