This study that telomere length is highly heritable in Arab families, which is consistent with several previous estimates based on sib pairs in a European Caucasian group . While the estimate is robust as to the influence of age, since it remains unchanged after adjustment for gender, generation and age within a generation, it is certainly an over-estimate of the genetic and epigenetic contribution to telomere length for two reasons: First, it fails to account for shared familial environmental influences (including activity levels and diet) that may affect telomere decay rates. Second, classically, the slope of a single parent-offspring regression is often considered to be twice the heritability, since only half of that parent's genes are transmitted to the child. Doubling the value would result in a nonsensical heritability estimate greater than 100%. The stronger paternal effect on the offspring's TL confirms several large-scale studies and reinforces the significant father-to-offspring heritage of longevity trait [13, 20].
Anthropometric parameters, such as BMI, body weight and waist and hip circumferences, were also highly heritable and related to telomere length in the present study, which means the susceptibility to obesity is evident in Arab families, and strengthens our previous finding that these measures of obesity, if deemed pathologic, predispose Arab children to accelerated ageing, as determined by shortened telomere lengths . Similarly, these findings are compatible with the high heritability of variations in the circulating levels of adipocytokines in the Arab population . However, whether the mean telomere lengths observed in this study for both parents and children are within the normal range cannot be determined, as there is no consensus as to what length is normal, probably because of the wide range of inter-individual variations and confounders observed in most studies .
Lastly, the association of telomere length to lipid parameters (total cholesterol and triglycerides) confirms our previous report . Elevated levels of cholesterol and triglycerides are atherogenic and confer metabolic stress that damages DNA and dampens telomerase activity leading to telomere length attrition . The link between cholesterol and telomere length is possibly due to increased cellular stress, which amplifies cell aging by damaging the telomerese by oxidation and by bringing cells to their maximum replicative capacity ultimately translating to shortened telomere length. This could also tie in with age-related innate immune pathway activation in adipose tissue and its link with sub-clinical systemic chronic inflammation .
This study has several limitations. Its cross-sectional nature limits our findings to mostly associations that are, at best, suggestive. Several confounders, such as diet and physical activity, were also not included. Nevertheless, the findings are strengthened by the homogeneity of the cohort studied. Dissemination of these results may have beneficial clinical implications for the ethnicity concerned, as they suggest that lifestyle changes and prevention are of utmost importance for both individual and public health.