Endocrine Abstracts

Introduction: Melatonin is a crucial hormone for controlling sleep rhythms and disruption of its natural secretory rhythmicity is considered to be one of the causes of type 2 diabetes mellitus. The MTNR1B gene encodes the melatonin receptor. Polymorphism rs10830963 in this gene shows an association with fasting blood glucose and impaired glucose tolerance. Current studies suggest that carriers of the minor allele G have a slightly shifted cycle of melatonin secretion toward a later rise in the evening and a slower decline in the morning, which may interact with social pressure on early morning activity and thus adversely affect glucoregulation. The aim of this study was to determine whether the polymorphism is projected into sleep patterns, biorhythms and chronotype evaluated through a questionnaire.

Methods: A total of 268 volunteers completed the MCTQ (Munich chronotype questionnaire) to determine sleep habits and chronotype. The average age did not differ significantly between the compared genotype groups. The ratio of women/men in the groups was also similar. Genotyping was performed on a TaqMan instrument (LC480, Roche), data were evaluated by NCSS/PASS 2020.

Results: Minor variant G was present in a heterozygous constellation in 124 participants (46%) and in a homozygous constellation in 26 (10%) with an allelic frequency of 33%. The remaining 118 individuals (44%) were homozygous in the common variant C. The average length of sleep on weekdays and days off did not differ between the groups, nor did the mid-sleep phase on weekdays and days off. The chronotype calculated from the mid-sleep phase values corrected for sleep debt accumulated during working days was also comparable. The time of subjective maximum daily activity was similar in all three genotype groups, with a median at 11 a.m. The social jat lag resulting from the discrepancy between the natural biorhythm and work/social duties averaged 0.85±0.698 h regardless of genotype. Interestingly, while in the groups with CG and CC genotype there were about 9% of people with very low caffeine consumption, in the group of homozygous GG carriers, individuals with low caffeine requirement were completely absent.

Conclusion: In the sample of the Czech population, we did not observe significant differences in sleep patterns and chronotype between the groups formed depending on the rs10830963 SNP genotype of the MTNR1B gene.Grant support: NU20-01-00308 and MZ CZ RVO EÚ00023761