Application of multiparametric procedures for assessing the heritability of circadian health

At present, the measurement of circadian system status under free-living conditions by the use of sensors is a relatively new technique. The data obtained using these methods are influenced by strong environmental masking factors and artifacts that can affect its recording. Therefore, the use of integrative variables such as TAP, a measure that includes temperature, activity and position that reduces these drawbacks and the number of parameters obtained is necessary. However, the relative genetic contribution to this circadian marker is unknown. The aim of our study was to ascertain the relative importance of genetic influences in TAP, and for each of its components using classical twin models. The study was performed in 53 pairs of female twins [28 monozygotic (MZ) and 25 dizygotic (DZ)] with mean age 52 ± 6 years. Circadian patterns were studied by analyzing temperature, body position and activity for 1 week every 1 min with "Circadianware®.". Genetic influences affecting the variability of each of the measurements were estimated by comparing the observed data in twin pairs. MZ twins showed higher intrapair correlations than DZ twins for most of the parameters. Genetic factors (broad sense heritability) were responsible for about 40-72% of TAP variance in parameters such as mesor, acrophase, amplitude, Rayleigh test, percentage of rhythmicity and circadian function index. We found more homogeneous heritability estimates of the circadian system when using an integrative technique such as TAP than with individual variables alone, suggesting that this measurement can be more reliable and less subject to environmental artifacts.