Background and aim Mild traumatic brain injury (mTBI) causes transient sleep disorders and circadian dysrhythmia. One of the clock genes, PERIOD3 (PER3), regulates the circadian rhythm and contains a genetic polymorphism, namely a variable-number tandem repeat in the coding area with either four or five repeats. PER35 carriers are inclined to have a morning preference and associated with higher risk of bipolar disorder and diabetes. This study investigated the effects of PER3 polymorphism on sleep quality changes after mTBI. Materials and methods From May 2012 to May 2014, a total of 96 mTBI patients completed the baseline (1 week after mTBI) and follow-up (6 weeks after mTBI) assessments, including the Pittsburgh Sleep Quality Index (PSQI) and anxiety and depression questionnaires. Statistics were analyzed using the Mann-Whitney U test, Wilcox signed-rank test or chi-squared test. Results Among the 96 patients, 24 were heterozygous PER35 carriers (PER34/5), and the rest of 72 were PER35 noncarriers (PER34/4). The subscale of PSQI questionnaire results indicated that the PER35 allele was associated with significant sleep duration shortening, but improvement in overall sleep quality. Furthermore, analyzing patients with sleep disturbance at the baseline (PSQI > 5) revealed that only the PER35 noncarriers exhibited a significant improvement in overall PSQI scores. Conclusion PER35 carriers exhibited sleep duration shortening and improved daytime function 6 weeks after mTBI compared with the baseline values. On the other hand, among poor sleepers, PER35 carriers did not embrace a significant improvement of overall PSQI scores as noncarriers. The underlying mechanisms and clinical significances must be investigated further.
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