On the one hand, sleep disorders contribute to progression of type 2 diabetes via hypothetical mechanisms, such as decreased brain glucose utilisation, altered orexin response, overactivation of the hypothalamus–pituitary–adrenal axis [71], suboptimal self-care (i.e. lower medication adherence [72]) and impaired decision-making (i.e. unhealthy diet and sedentary behaviour) [73]. The gene discussed is HCRT; the disease is type 2 diabetes mellitus.