Major gene effect on subcutaneous fat distribution in a sedentary population and its response to exercise training: The HERITAGE family study

Complex segregation analysis of baseline subcutaneous fat distribution and the change in response to exercise training (post-training minus baseline indices) was performed in a sample of 482 individuals from 99 Caucasian families who participated in the HERITAGE Family Study. The sum of skinfold (SF) thicknesses at eight sites, and the waist and hip circumferences were measured at baseline and after completing a 20-week exercise training program. The trunk-to-extremity ratio (TER) was calculated by dividing the sum of skinfold thicknesses at four trunk sites (subscapular + suprailiac + abdominal + midaxillary) by the sum of skinfold thicknesses at four extremity sites (triceps + biceps + medial calf + thigh). While SF was used to assess total subcutaneous adiposity, TER and the ratio of the waist-to-hip circumferences (WHR) were used to characterize subcutaneous fat distribution. Baseline TER and WHR were age-adjusted and age-SF-adjusted within four sex-by-generation groups. The changes of SF, TER, and WHR in response to training were adjusted for age effects alone and for the effects of age and baseline values. Baseline SF was influenced by a multifactorial component (30%) plus a major effect that may be environmental in origin accounting for 47% of the variance. Baseline TER was influenced by a multifactorial component (18%) and a major codominant gene (q² = 0.10), which accounted for 56% of the variance. The major gene effect was independent of total subcutaneous adiposity. Baseline WHR was regulated by a major Codominant gene (q² = 0.15), which accounted for 48% of the variance. However, this major gene effect for baseline WHR should be interpreted with caution, given the estimates of the T'S under the general model. No familial effect was found for the changes in response to training for these subcutaneous adipos-ity and fat distribution phenotypes.