INTRODUCTION: Genetics is behind our circadian machinery. CLOCK (Circadian Locomotor Output Cycles Kaput) 3111T/C single-nucleotide polymorphism (SNP) has been previously related to obesity and weight loss. However, phenotypic association and functionality of CLOCK 3111 locus is still unknown. The aim of this study was to determine, in free-living conditions, if the presence of CLOCK 3111C in overweight women could be related to (a) circadian disorders, and (b) changes in sleep quality, to improve understanding of the previously demonstrated associations with obesity and reduced weight loss of the C carriers.
METHODS: Wrist temperature, actimetry and position (TAP) and TAP variables were measured as markers of circadian functionality during 8 consecutive days. A rest-activity and food diary was also completed, whereas sleep quality was determined by domiciliary polysomnography. We recruited 85 women who were overweight with body mass index (BMI) of 28.59±4.30 kg m(-2) and age 43±12 years. From this sample, we found that 43 women were carrying the minor allele (C) for CLOCK 3111T/C SNP and 42 women were TT carriers (major allele carriers). Both groups of patients were matched for number, age, obesity parameters and energy intake.
RESULTS: Compared with TT subjects, who showed more robust circadian rhythm profiles, patients with the C allele displayed significant circadian abnormalities: lower amplitude and greater fragmentation of the rhythm, a less stable circadian pattern and a significantly weakened circadian function, as assessed by the circadian function index (CFI). C subjects were also less active, started their activities later in the morning and were sleepier during the day, showing a delayed acrophase that characterizes 'evening-type' subjects.
CONCLUSION: C genetic variants in CLOCK 3111T/C display a less robust circadian rhythm than TT and a delayed acrophase that characterizes 'evening-type' subjects. We support the notion that identifying CLOCK genotypes in patients may assist the therapist in characterization of the roots of the metabolic problem.
