Major gene with sex-specific effects influences fat mass in Mexican Americans.

Increased adiposity has repeatedly been identified as a major risk factor for a variety of chronic diseases. However, the question still remains whether the amount of adipose tissue itself is genetically mediated. To address this question, a segregation analysis, using maximum likelihood techniques as implemented in the computer program Pedigree Analysis Package (PAP), was performed on fat mass (kilograms of body fat) in a large sample of extended Mexican American families residing in San Antonio, TX. The only model not rejected was a Mendelian mixed model for fat mass, incorporating genotype x sex interaction. In males the major gene accounted for 37% of the total variance compared with 43% in females. In both sexes homozygous recessive individuals have a fat mass more than double that of individuals of the other two genotypes. It was possible to reject linkage of the anonymous major gene for fat mass with several candidate loci for obesity. However, tentative evidence of linkage was detected with markers on both chromosomes 2 and 11, thereby providing hypotheses for future testing.