Journals of Gerontology Series A: Biological Sciences and Medical Sciences, Vol 55, Issue 1 B49-B53, Copyright © 2000 by The Gerontological Society of America
The contribution of genetic influences to measures of lower-extremity function in older male twins
D Carmelli, M Kelly-Hayes, PA Wolf, GE Swan, LM Jack, T Reed and JM Guralnik
Center for Health Sciences, SRI International, Menlo Park, California 94025, USA. [email protected]
Tests of balance, gait, and endurance were administered to 95 monozygotic
(MZ) and 92 dizygotic (DZ), white male twins aged 68 to 79 years who had
been born in the United States. Within-twin-pair correlations were
calculated for each individual task and for an overall summary performance
score. These were subjected to structural equation modeling to determine
the contributions of genetic and environmental influences to individual
differences in performance scores. MZ intraclass correlations were
significant and greater than DZ correlations for the 8-foot walk and the
repeated chair stands task, but not for the standing balance task. The
heritability of the lower- extremity summary score was 57%, of which 39%
was due to additive genetic effects and 18% due to nonadditive effects. In
addition, we found that genetic influences contributed primarily to twin
similarity in the poorest quartile of performance, whereas shared
environmental influences contributed to twin similarity in the best
quartile.
