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

Numerous studies have shown recessive major gene inheritance of body mass i ndex (BMI) in white populations; few have examined the inheritance of BMI i n the African-American population where obesity is more prevalent, nor in A frican populations where obesity is comparatively rare. To evaluate the inh eritance of obesity in two different populations of African origin, we used segregation analysis to determine the transmission of BMI in 95 African-Am erican families and 400 Nigerian families. Probands were selected from part icipants in the population-based International Collaborative Study on Hyper tension in Blacks. Using class D regressive models, results from the segreg ation analysis of the African-American data showed evidence of a major gene effect on BMI. The Nigerian results were strikingly similar, with comparab le estimates for the genotype frequencies and means and strong evidence for a major effect in the transmission of BMI. The high BMI allele frequency e stimate of 24% is consistent with estimates in other studies, but the mode of transmission appeared codominant, which differs from studies involving p redominantly white populations. In the Nigerian analysis, however, the prob ability of a high BMI homozygote parent transmitting a low BMI allele to hi s/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. (C) 2000 Wiley-Liss, Inc.