PER3 gene regulation of sleep-wake behavior as a function of latitude.

OBJECTIVES: We searched for interactions between PER3 gene VNTR polymorphism, latitude, sleep duration, diurnal sleepiness, and social jetlag.

DESIGN: We selected samples from 3 distinct cities along the latitudinal range of Brazil and comprising the same time zone.

SETTING: Undergraduate universities located in 3 major cities of Brazil.

PARTICIPANTS: A total of 980 undergraduate students: 276 from Maceio (latitude 9°), 358 from Campinas (latitude 22°), and 346 from Porto Alegre (latitude 30°).

MEASUREMENTS: PER3 variable number of tandem repeats genotyping, diurnal sleepiness, sleep duration (weekdays and weekend), chronotype, and social jetlag.

RESULTS: Latitude is associated with a differential expression of circadian and sleep profiles. We observed a shift toward eveningness with increased latitude and increased social jetlag and diurnal sleepiness at latitude 30°. Moreover, our results suggest that the PER3 variable number of tandem repeats polymorphism has a modulatory effect on these circadian and sleep profiles: the variant PER34/4 is associated with a smaller difference in the sleep duration on weekdays among different latitudes and is associated with longer sleep duration on weekends just at latitude 30°, even when compared to both other genotypes at the same latitude. On the other hand, irrespective of the genotype, volunteers from latitude 30° expressed increased social jetlag and diurnal sleepiness.

CONCLUSIONS: The seasonal variation in the light/dark cycle, tied to latitude, together with the tight social time constraints that young adults are subjected to during weekdays, generates differences in the sleep phenotypes. Volunteers with the PER34/4 variant who live farther from the equator have a greater increase in their weekend sleep duration.