4 and 7 In Brazil, this is the first study that attempts to assess the association between sleep duration and obesity in children, correlating it to a genetic variation involved in the biological rhythm control of several hormonal and metabolic variables.22 One of the main genes involved
in the modulation of circadian rhythm is the CLOCK gene, a transcription factor expressed in different tissues that has been implicated in the regulation of metabolic processes such as insulin secretion, 23 hypothalamic action of leptin, 13 nutrient absorption, 24 and sensitivity to glucocorticoids. 25 The polymorphism 3111T/C, located in the 3′‐untranslated gene region, has been associated with feeding behavior control, hormone secretion, learn more mood, and sleep; therefore, it was selected as a candidate SNP for the study of the molecular association
between sleep duration and obesity in children. 16 and 18 Previous observations attributed a phenotype of overweight and short sleep duration to genotype C*. An interesting study involving 1,290 obese individuals of both genders, aged 20 to 69 years, observed that patients with at least one C allele had shorter sleep duration when compared with individuals homozygous for the T allele, as well as weight loss resistance, higher serum levels of ghrelin, and nocturnal feeding habits.15 In the present sample, a higher prevalence of overweight and shorter duration Oxalosuccinic acid of sleep was observed in individuals homozygous Selleckchem VE-821 for the C allele; although consistent with previous results, this difference was not statistically significant. A negative result for this association has been described by other studies.18 and 26 One possible explanation for the divergent results is the statistical power limitation of this sample,
as the study had limitations in terms of cost and logistics for expanding sample size. Another possibility is that the association reported in previous studies is not directly related to a causal effect of this polymorphism. Although the functional role of the polymorphism on the mRNA stability has been demonstrated,27 the possibility of linkage disequilibrium with another truly functional polymorphism cannot be discarded, as the degree of linkage may vary depending on the genetic profile of each population. Only one study involving this polymorphism in a Brazilian sample was retrieved in the literature, which showed no significant association between genotype and sleep pattern in adults.26 In this study, in which 162 adults of both genders were genotyped for the 3111 T/C polymorphism of the CLOCK gene, the observed genotypic frequencies (7% CC, 40% CT, and 53% TT) were similar to those in the present study, which are also compatible with the classically described frequencies in the dbSNP database (rs 1801260).