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Length polymorphism in the P eriod 3 gene is associated with sleepiness and maladaptive circadian phase in night‐shift workers
Author(s) -
Drake Christopher L.,
Belcher Ren,
Howard Ryan,
Roth Thomas,
Levin Albert M.,
Gumenyuk Valentina
Publication year - 2015
Publication title -
journal of sleep research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 117
eISSN - 1365-2869
pISSN - 0962-1105
DOI - 10.1111/jsr.12264
Subject(s) - circadian rhythm , epworth sleepiness scale , melatonin , morning , shift work , sleep deprivation , medicine , psychology , endocrinology , polysomnography , psychiatry , apnea
Summary The objective of the current study was to determine if night‐shift workers carrying the five‐repeat variant of the Period 3 gene show elevated levels of nocturnal sleepiness and earlier circadian phase compared with homozygotes for the four‐repeat allele. Twenty‐four permanent night‐shift workers were randomly selected from a larger study. Participants took part in an observational laboratory protocol including an overnight multiple sleep latency test and half‐hourly saliva collection for calculation of dim‐light melatonin onset. Period 3 –/5 shift workers had significantly lower multiple sleep latency test during overnight work hours compared with Period 3 4/4 workers (3.52 ± 23.44 min versus 10.39 ± 6.41 min, P = 0.003). We observed no significant difference in sleepiness during early morning hours following acute sleep deprivation. Long‐allele carriers indicated significantly higher sleepiness on the Epworth Sleepiness Scale administered at 17:00 hours (12.08 ± 2.55 versus 8.00 ± 1.94, P < 0.001). We observed a significantly earlier melatonin onset in Period 3 –/5 individuals compared with Period 3 4/4 shift workers (20:44 ± 6:37 versus 02:46 ± 4:58, P = 0.021). Regression analysis suggests that Period 3 genotype independently predicts sleepiness even after controlling for variations in circadian phase, but we were unable to link Period 3 to circadian phase when controlling for sleepiness. Period 3 –/5 shift workers showed both subjective and objective sleepiness in the pathological range, while their Period 3 4/4 counterparts showed sleepiness within normal limits. Period 3 –/5 night workers also show a mean circadian phase 6 h earlier (i.e. less adapted) than Period 3 4/4 workers. Because Period 3 –/5 workers have maladaptive circadian phase as well as pathological levels of sleepiness, they may be at greater risk for occupational and automotive accidents. We interpret these findings as a call for future research on the role of Period 3 in sleepiness and circadian phase, especially as they relate to night work.