Lack of association between PER3 variable number tandem repeat and circadian rhythm sleep-wake disorders.

Circadian rhythm sleep-wake disorders (CRSWDs) are characterized by disturbed sleep-wake patterns. We genotyped a PER3 variable number tandem repeat (VNTR) in 248 CRSWD individuals and 925 controls and found no significant association between the VNTR and CRSWDs or morningness-eveningness (diurnal) preferences in the Japanese population. Although the VNTR has been associated with circadian and sleep phenotypes in some other populations, the polymorphism may not be a universal genetic marker.