title: The contribution of genetic influences to measures of lower-extremity function in older male twins.
abstract: 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.
authors.affiliation: Center for Health Sciences, SRI International, Menlo Park, California 94025, USA. doritc@unix.sri.com
authors.forename: D
authors.initials: D
authors.lastname: Carmelli
authors.forename: M
authors.initials: M
authors.lastname: Kelly-Hayes
authors.forename: P A
authors.initials: PA
authors.lastname: Wolf
authors.forename: G E
authors.initials: GE
authors.lastname: Swan
authors.forename: L M
authors.initials: LM
authors.lastname: Jack
authors.forename: T
authors.initials: T
authors.lastname: Reed
authors.forename: J M
authors.initials: JM
authors.lastname: Guralnik
mesh_terms: D000368:Aged; D000375:Aging / Q000502:physiology*; D000704:Analysis of Variance; D016009:Chi-Square Distribution; D004185:Disability Evaluation; D005684:Gait / Q000502:physiology*; D006801:Humans; D007866:Leg; D016013:Likelihood Functions; D008297:Male; D010807:Physical Endurance / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D014427:Twins / Q000235:genetics*; D014429:Twins, Dizygotic / Q000235:genetics; D014430:Twins, Monozygotic / Q000235:genetics