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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.