Population differences in the pattern of familial aggregation for sex hormone-binding globulin and its response to exercise training: The HERITAGE Family Study

Familial influences were investigated for baseline sex hormone-binding glob ulin (SHBG) and its response (post-training minus baseline) to a 20-week en durance exercise training program. One hundred, eighty-four participants fr om 85 Black families in the HERITAGE Family Study (HERITAGE) were analyzed using a familial correlation model. Baseline SHBG values and the training r esponse were adjusted for the effects of age, baseline BMI, testosterone, e stradiol, and fasting insulin levels (plus baseline SHBG values for the tra ining response) within four sex-by-generation groups prior to genetic analy sis. Baseline SHBG levels were influenced by appreciable familial effects ( maximum heritability h(2) = 54%) with neither spouse resemblance nor sex an d generation differences in the correlations. This estimate is only slightl y, but not significantly, smaller than the heritability of 64% reported pre viously in 428 participants from 99 White families in HERITAGE. In contrast to the modest familial effects for the training response in White particip ants in HERITAGE (h(2) = 25%), there were no evidence of familial resemblan ce in Blacks in the current study. Furthermore, there was heterogeneity for both baseline SHBG and the training response between Blacks and Whites in the pattern of familial aggregation. In conclusion, baseline SHBG levels ar e influenced by significant familial effects in both Blacks and Whites, ind ependent of the effects of age, sex, and baseline values of BMI. testostero ne, estradiol, and fasting insulin levels. Whereas modest familial effects were detected for the training response in Whites, the lack of similar effe cts in Blacks may be due to the smaller sample size. (C) 2001 Wiley-Liss, I nc.