Genetic and environmental influences on functional abilities in Danish twins aged 75 years and older

Background. Functional abilities vary widely among elderly persons. The det erminants of this variation are probably multiple and include normal aging processes as well as disease expression. This study estimates the relative importance of genetic and environmental factors to variation in functional abilities in elderly persons. Methods. We conducted a survey among all Danish twins aged 75 years and old er who were identified in the population-based Danish Twin Registry. interv iews were conducted with 77% (7% by proxy responders) of the 3099 individua ls in the study population. Functional abilities were assessed by validated Danish survey instruments and were scored on three scales. Heritability (p roportion of the population variance attributable to genetic variation) was estimated using structural equation analyses. Results. Structural equation analyses revealed a substantial heritability ( 33%-47%) for the three functional ability scores among the women aged 80 ye ars and older compared with a more modest heritability (15%-34%) among the women aged 75-79 years. The remaining variation could be attributed to indi viduals' nonfamilial environments. Comparisons of the functional abilities of twins with living versus deceased co-twins also suggested a difference i n the genetic influence for the two age group. Although heritability estima tes were uniformly low in the male participant sample, the size of the samp le was not sufficiently large to allow for precise estimates of heritabilit y. Conclusion. For women we found that the effect of genetic factors on functi onal abilities increases with age and accounts for one third to one half of the variation among individuals aged 80 Sears and older. An understanding of the genetic mechanisms underlying functional abilities in the oldest ind ividuals may enhance the possibilities for improving health in the elderly population by modifying environmental factors.