PER3 and insomnia: Genetic variations could explain some phenotypic consequence, such as duration of sleep, waketime, addiction, insomnia, day preferences, etc. In our work, we noticed that the polymorphisms rs238666 in the PER3 and the rs4580704 in the CLOCK gene were associated with sleep duration and the rs1051061 and rs848291 in the VRK2 with waketimes.