Genetic inheritance of body mass index in African-American and African families.

Numerous studies have shown recessive major gene inheritance of body mass index (BMI) in white populations; few have examined the inheritance of BMI in the African-American population where obesity is more prevalent, nor in African populations where obesity is comparatively rare. To evaluate the inheritance of obesity in two different populations of African origin, we used segregation analysis to determine the transmission of BMI in 95 African-American families and 400 Nigerian families. Probands were selected from participants in the population-based International Collaborative Study on Hypertension in Blacks. Using class D regressive models, results from the segregation analysis of the African-American data showed evidence of a major gene effect on BMI. The Nigerian results were strikingly similar, with comparable estimates for the genotype frequencies and means and strong evidence for a major effect in the transmission of BMI. The high BMI allele frequency estimate of 24% is consistent with estimates in other studies, but the mode of transmission appeared codominant, which differs from studies involving predominantly white populations. In the Nigerian analysis, however, the probability of a high BMI homozygote parent transmitting a low BMI allele to his/her offspring was significantly different from the Mendelian expectation of zero (estimated tau(BB) = 0.45), suggesting that additional complexities exist in the major gene inheritance of BMI in this population. The strong similarity of the genotype frequencies and means obtained from the African-American and Nigerian samples suggests that a common codominant major gene effect may contribute to the variation in BMI in both populations.