Within birth cohort segregation analyses support recessive inheritance of body mass index in white and African-American families

OBJECTIVE : We conducted segregation analyses of body mass index within birth cohort to determine whether previously reported support for recessive major gene inheritance in white and African-American families could have been due to higher rates of obesity in offspring than in parents, which are caused by temporal increases in obesity in recent decades. DESIGN : Segregation analysis of family data. MEASUREMENT : The body mass index (BMI), adjusted for effects of gender, linear and non-linear effects of age, education and occupation of head of household, and clinic from which family was ascertained. RESULTS : Segregation analysis results support a recessive mode of major gene inheritance of body mass index, even though we restricted our analysis to siblings born within the same post-1945 cohort. We also found support for substantial polygenic heritability of body mass index, which is consistent with a multigenic heritability. There was no significant heterogeneity between white and African-American families in support for a recessive mixed model. However, some differences in particular parameters were found, with higher gene frequency, lower polygenic heritability and a larger variance associated with the major gene model in African-Americans. CONCLUSION : Our present segregation analysis shows that the recessive pattern, whether due to single or multiple genes, cannot be explained by inter-generational differences in obesity prevalence or family correlation. There was suggestive evidence of a higher major gene frequency and larger gene effect size in African-American families.