Objective: African Americans have a particularly high prevalence of excessive body fat and high blood pressure. Genetic and environmental influences may be implicated for both of these risk factors. We investigated the potential for common genetic and environmental influences on body fat (waist circumference (WC), body mass index (BMI)) and blood pressure measures (systolic and diastolic pressure (SBP, DBP)) among African-American male and female subjects.
Research methods and procedures: Measurements were taken as part of the Carolina African-American Twin Study of Aging (CAATSA). The CAATSA sample contains 217 same-sex African-American male and female twins with average age of 47 years. This analysis included 39 monozygotic male pairs (MZ), 43 dizygotic male pairs (DZ); 63 MZ female pairs, and 72 DZ female pairs. Maximum likelihood quantitative genetic analyses were used.
Results: The total genetic variance for SBP was 22% in male subjects and 40.1% in female subjects. Of this total variance, 3.1% was in common with BMI in male subjects and 6% was in common with BMI in female subjects. After controlling for the effects of BMI, WC had less than 1% of its variance in common with SBP in male and female subjects. For DBP, the total genetic variance was 16.9% in male and 38.7% in female subjects. Of this total variance 6.1% was in common with BMI in male subjects and 3.7% was in common in female subjects. Again, WC had less than 1% of its genetic variance in common with DBP in both male and female subjects. The environmental variance common among these measures was also very small. The remaining variance was primarily accounted for by genetic and environmental effects unique to each measure as well as age.
Discussion: Based on the very small common genetic variance for BMI, SBP, and DBP as well as WC and the blood pressure measures, our results suggest that searching for common genes among these measures may be inconclusive.