Scott M. Hofer1, S. Berg2, B. Johansson2, G. E. McClearn1
The development and aging of cognitive capabilities are sensitive to many influences throughout the lifespan. In a recent study (G. E. McClearn, B. Johansson, S. Berg, N. L. Pedersen, F. Ahern, S. A. Petrill, & R. Plomin, 1997, Science,276n, 1560-1563), specific and general cognitive abilities were found to remain substantially heritable in late life. Previous findings from other longitudinal twin studies indicate that genetic effects contribute more to stability than to change throughout adulthood. In this study, we investigated the relative contributions of environmental and genetic factors to longitudinal change and continuity in specific and general cognitive functioning. The focus of these analyses was on the concordance between twins in intraindividual variability rather than on interindividual differences in cognitive performance. These analyses were performed on data from the OCTO-Twin study of octogenarian and nonagenarian twins measured at three occasions with two-year inter-occasion intervals. Multivariate analyses of cognitive change included health status and health behaviors, sensory acuity, and measures of lifestyle. Models with missing data due to attrition (due mainly to mortality) were estimated assuming the data were "missing at random" (e.g., including covariates and previous outcome variables associated with dropout status). In general, the findings concur with previous results of substantial stability in the genetic factors associated with cognitive functioning.
Address: Center for Developmental and Health Genetics, The Pennsylvania State University, 101 Amy Gardner House, University Park, PA 16802, P: (814) 865-1717 F: (814) 863-4768, smhofer@cdhg.psu.edu
1Center for Developmental and Health Genetics, Pennsylvania State University, University Park, PA 16802 2Institute of Gerontology, University College of Health Sciences, Box 1038, S-551 11 Jonkoping, Sweden. 3Supported by NIA Grant AG08861.