Total body fat and abdominal visceral fat response to exercise training in the HERITAGE family study: Evidence for major locus but no multifactorial effects

The familial etiology of the response in total fat mass (FM) and abdominal visceral fat (AVF) to 20 weeks of exercise training was investigated in families participating in the HERITAGE Family Study. AVF (measured by computed tomographic scanning) and FM (measured by underwater weighing techniques) were assessed at baseline (in a sedentary state) and after 20 weeks of exercise training. The response AVF (AVFΔ) and response FM (FMΔ) were computed as the simple delta values (posttraining — baseline) and adjusted for the effects of sex, generation, and a polynomial in age using multiple regression analysis. To index the AVF response independently of the response in FM and the initial level of visceral fat, the AVFΔ was also adjusted for age and baseline AVF (AVFB) and FMΔ. Familial correlation analysis was used to investigate the multifactorial familial effects (polygenic and/or familial environmental), and segregation analysis was used to search for major gene effects. For the age-adjusted AVFΔ, a putative recessive locus accounting for 18% of the variance (q 2 = 1%) was detected. Adjusting AVFΔ for AVFB and FMΔ slightly increased the percentage of variance accounted for (to 26%, q 2 = 3%) but did not radically alter the pattern of the parameter estimates. For FMΔ, a putative dominant locus accounting for 31% of the variance (q 2 = 49%) was noted. In conclusion, the results were consistent across methods in suggesting that there is little evidence of a multifactorial heritability for either AVFΔ or FMΔ. Rather, the familial etiology of the response to exercise training appears to be primarily due to putative major genes (a recessive locus for AVFδ and a dominant locus for FMΔ). In addition, a pleiotropic/oligogenic system underlying these variables was inferred. That is, the putative loci for FMΔ and/or AVFB also may impact the AVFΔ, with an additional independent major locus effect on AVFΔ after the former influences have been removed.