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

PER3gene 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 twoPER3polymorphic 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 inPER34/PER34andPER35/PER35homozygotes. 786 Caucasian subjects living in Northern Italy donated buccal DNA and completed diurnal preference, sleep quality/timing and sleepiness/mood questionnaires. 19PER34/PER34and 11PER35/PER35homozygotes 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 thePER3Gvariant and morningness (OR = 2.10), and between thePER3G-PER34haplotype and morningness (OR = 2.19), for which a mechanistic hypothesis is suggested. No significant differences were observed in sleep timing/aMT6s rhythms betweenPER35/PER35andPER34/PER34subjects at baseline. After light administration,PER34/PER34subjects advanced their aMT6s acrophase (p < 0.05), and showed a trend of advanced sleep-wake timing. In conclusion, significant associations were observed betweenPER3polymorphic variants/their combinations and both diurnal preference and the response to light.