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

Functional abilities vary widely among elderly persons. The determinants of this variation are proba-bly multiple and include normal aging processes as well as disease expression. This study estimates the relative impor-tance 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 older who were identified in the popu-lation-based Danish Twin Registry. Interviews were conducted with 77 % (7 % by proxy responders) of the 3099 individ-uals in the study population. Functional abilities were assessed by validated Danish survey instruments and were scored on three scales. Heritability (proportion of the population variance attributable to genetic variation) was estimated using structural equation analyses. Results. Structural equation analyses revealed a substantial heritability (34%–47%) for the three functional ability scores among the women aged 80 years and older compared with a more modest heritability (15%–34%) among the women aged 75–79 years. The remaining variation could be attributed to individuals ’ nonfamilial environments. Com-parisons of the functional abilities of twins with living versus deceased co-twins also suggested a difference in the ge-netic influence for the two age groups. Although heritability estimates were uniformly low in the male participan