Common functional polymorphisms in SLC6A4 and COMT genes are associated with circadian phenotypes in a South American sample.

The molecular study of circadian rhythms in humans could be an excellent approach to understand the relation between genes and behavior. It is possible that variations in genes involved in neurotransmission and/or synaptic plasticity, such as catechol-O-methyltransferase (COMT) and serotonin transporter (SLC6A4) could be of particular interest in understanding human circadian phenotypes. The aim of this study is to analyze the possible and novel associations of the functional polymorphisms in COMT and SLC6A4 genes (Val158Met and 5-HTTLPR) and circadian phenotypes in healthy Colombian subjects. 191 university students were genotyped for two functional polymorphisms in COMT and SLC6A4 genes (rs4680 and rs4795541). We applied two scales to measure phenotypic patterns of human circadian rhythms: Composite Scale of Morningness (CSM) and Epworth Sleepiness Scale (ESS). We found a significant association between 5-HTTLPR polymorphism and morning preference score (CSM) (p = 0.027) using an overdominant genotypic model and association of COMT Val158Met with daytime sleepiness (ESS scores) (p = 0.038) in a genotypic recessive model. These results were supported by differences in genotype frequencies between circadian typologies for SLC6A4 gene (p = 0.007) and categories of diurnal sleepiness for COMT gene (p = 0.032). Our results suggest, for the first time, a significant relationship between functional SLC6A4 and COMT polymorphisms with specific human circadian phenotypes: morning preference and diurnal sleepiness. These results need to be replicated in other populations. Further study of functional polymorphisms in other synaptic genes could be of relevance for the identification of novel candidate genes for circadian phenotypes, and related endophenotypes of neuropsychiatric importance, in healthy humans.

Study of a Functional Polymorphism in the PER3 Gene and Diurnal Preference in a Colombian Sample.

Polymorphisms in human clock genes have been evaluated as potential factors influencing circadian phenotypes in several populations. There are conflicting results for the association of a VNTR in the PER3 gene and diurnal preference in different studies. The objective of this study was to investigate the association between diurnal preference and daytime somnolence with the PER3 VNTR polymorphism (rs57875989) in healthy subjects from Colombia, a Latin American population.A total of 294 undergraduate university students from Bogotá, Colombia participated in this study. Two validated self-report questionnaires, the Composite Scale of Morningness (CSM) and the Epworth Sleep Scale (ESS) were used to assess diurnal preference and daytime somnolence, respectively. Individuals were genotyped for the PER3 VNTR using conventional PCR. Statistical comparisons were carried out with PLINK and SNPStats programs. The PER3 VNTR polymorphism was not associated with either diurnal preference or daytime somnolence in this population. No significant differences in mean scores for those scales were found between PER3 VNTR genotypes. In addition, there were no differences in allelic or genotypic frequencies between chronotype categories. This is consistent with several negative findings in other populations, indicating that the proposed influence of this polymorphism in diurnal preference, and related endophenotypes of neuropsychiatric importance, needs further clarification. This is the first report of molecular genetics of human circadian phenotypes in a Spanish-speaking population.

A novel association of two non-synonymous polymorphisms in PER2 and PER3 genes with specific diurnal preference subscales.

The circadian system is responsible for the generation and maintenance of physiological and behavioral rhythms in mammals and allows synchronization with the environment. Different polymorphisms in clock genes have been studied in healthy humans, providing inconsistent results in different populations. In this study, we evaluated the possibility that two non-synonymous polymorphisms in PER2 (p.Gly1244Glu, rs934945) and PER3 (p.Met1028Thr, rs2640909) genes might be associated with diurnal preference in healthy Colombian subjects. A total of 209 Colombian university students were genotyped for two functional polymorphisms in PER2 and PER3 genes (rs934945 and rs2640909). We applied the composite scale of morningness (CSM) to measure phenotypic patterns of human diurnal preference. Additionally, we extracted from the CSM three subscale scores ("morningness", "activity planning" and "morning alertness"). We used a false discovery rate approach (q values) for correction of multiple testing. PER2 (rs934945) showed a significant association with two CSM subscale scores: "activity planning" and "morning alertness". For PER3 (rs2640909), we observed an association with the "morningness" CSM subscale scores. We found a significant association between novel and functional polymorphisms in PER2 and PER3 genes with specific CSM subscales for diurnal preference. We showed for the first time the association of rs934945 with "morning alertness" and rs2640909 with "morningness". We suggest that these results should be replicated in order to confirm the association in other populations. Finally, the study of additional novel functional polymorphisms in other clock genes could be of relevance for a deep understanding of circadian phenotypes and neuropsychiatric disorders.