The contribution of genetic influences to measures of lower-extremityfunction in older male twins

Abstract

Tests of balance, gait, and endurance were administered to 95monozygotic (MZ) and 92 dizygotic (DZ), white male twins aged 68 to 79years who had been born in the United States. Within-twin-pair correlationswere calculated for each individual task and for an overall summaryperformance score. These were subjected to structural equation modeling todetermine the contributions of genetic and environmental influences toindividual differences in performance scores. MZ intraclass correlationswere significant and greater than DZ correlations for the 8-foot walk andthe repeated chair stands task, but not for the standing balance task. Theheritability of the lower- extremity summary score was 57%, of which 39%was due to additive genetic effects and 18% due to nonadditive effects. Inaddition, we found that genetic influences contributed primarily to twinsimilarity in the poorest quartile of performance, whereas sharedenvironmental influences contributed to twin similarity in the bestquartile.