SEGREGATION ANALYSIS OF FAT MASS AND OTHER BODY-COMPOSITION MEASURES DERIVED FROM UNDERWATER WEIGHING

Segregation patterns of three body composition measures which were der ived from underwater weighing were evaluated in a random sample of 176 French-Canadian families. Two of the variables can be considered as p rimary partitions of weight (fat mass [FM] and fat-free mass [FFM]), w hile the remaining variable (percent body fat [%BF]) is a derived inde x combining the measures of both fat and fat-free weight. This study r epresents the first report investigating major gene effects for these measures. Segregation analyses revealed that a major locus hypothesis could not be rejected for two of the three phenotypes. The single exce ption was FFM, for which nearly 60% of the variance was accounted for by a non-Mendelian major effect, which may reflect environmentally bas ed commingling or may be in part a function of gene-environment intera ctions or correlations. In contrast to the results for FFM, the result s for each of FM and %BF were similar and suggested a major locus whic h accounted for 45% of the variance, with an additional 22%-26% due to a multifactorial component. Given the similarity of the major gene ch aracteristics for these two phenotypes, the possibility that the same gene underlies both measures warrants investigation. A reasonable hypo thesis is to consider genes that may influence nutrient partitioning, as the family of candidate genes to receive the major attention.