MAJOR GENE WITH SEX-SPECIFIC EFFECTS INFLUENCES FAT MASS IN MEXICAN-AMERICANS

Increased adiposity has repeatedly been identified as a major risk fac tor for a variety of chronic diseases. However, the question still rem ains whether the amount of adipose tissue itself is genetically mediat ed. To address this question, a segregation analysis, using maximum li kelihood techniques as implemented in the computer program Pedigree An alysis 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 mod el for fat mass, incorporating genotype X sex interaction. In males th e 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 evid ence of linkage was detected with markers on both chromosomes 2 and 11 , thereby providing hypotheses for future testing. (C) 1995 Wiley-Liss , Inc.