A variable number tandem repeat (VNTR) polymorphism in Per3 (Dijk and Archer 2010) has been associated with chronotype, sleep homeostasis and various psychiatric disorders (Andrade-Silva et al. 2014; Li and Cassone 2015; Morioka et al. 2010; Terazono et al. 2003). The gene discussed is PER3; the disease is psychiatric disorder.