GENETIC AND ENVIRONMENTAL CORRELATIONS AMONG HORMONE LEVELS AND MEASURES OF BODY-FAT ACCUMULATION AND TOPOGRAPHY

In this study we partition the phenotypic correlations between body fa t measures and serum levels of hormones with known, or suspected, lipo lytic effects into their genetic and environmental components. Using v ariance decomposition techniques, we are able to estimate the pleiotro pic effects of genes and/or shared environmental factors that give ris e to the phenotypic correlations previously reported between these tra its. We used data from a large sample of randomly ascertained Mexican- American families living in San Antonio, TX. Data were available for 5 82 individuals in 26 pedigrees. Levels of sex hormone-binding globulin , dehydroepiandrosterone sulfate, insulin, insulin-like growth factor I, total T-4, and total T-3 were assayed. The measures of body fat acc umulation and topography included body mass index, subscapular/triceps ratio, and relative fat patterning index. The results of this analysi s demonstrate that significant phenotypic correlations among these tra its can arise from three underlying conditions: 1) entirely from share d genetic effects (pleiotropy), 2) entirely from shared random environ mental effects, or 3) a combination of both effects. However, we also show that it is possible for significant genetic and environmental cor relations to interact in such a way as to produce a phenotypic correla tion that itself would not be considered significant.