Diurnal preference, mood and the response to morning light in relation to polymorphisms in the human clock gene PER3

PER3 gene polymorphisms have been associated with differences in human sleep-wake phenotypes, and sensitivity to light. The aims of this study were to assess: i) the frequency of allelic variants at two PER3 polymorphic sites (rs57875989 length polymorphism: PER34, PER35; rs228697 SNP: PER3C, PER3G) in relation to sleep-wake timing; ii) the effect of morning light on behavioural/circadian variables in PER34/PER34 and PER35/PER35 homozygotes. 786 Caucasian subjects living in Northern Italy donated buccal DNA and completed diurnal preference, sleep quality/timing and sleepiness/mood questionnaires. 19 PER3 4 /PER3 4 and 11 PER3 5 /PER3 5 homozygotes underwent morning light administration, whilst monitoring sleep-wake patterns and the urinary 6-sulphatoxymelatonin (aMT6s) rhythm. No significant relationship was observed between the length polymorphism and diurnal preference. By contrast, a significant association was observed between the PER3G variant and morningness (OR = 2.10), and between the PER3G-PER34 haplotype and morningness (OR = 2.19), for which a mechanistic hypothesis is suggested. No significant differences were observed in sleep timing/aMT6s rhythms between PER35/PER35 and PER34/PER34 subjects at baseline. After light administration, PER34/PER34 subjects advanced their aMT6s acrophase (p PER3 polymorphic variants/their combinations and both diurnal preference and the response to light.