A biometric latent curve analysis of memory decline in older men of the NAS-NRC twin registry.
Previous research has shown cognitive abilities to have different biometric patterns of age-changes. We examined the variation in episodic memory (word recall task) for over 6,000 twin pairs who were initially aged 59-75, and were subsequently re-assessed up to three more times over 12 years. In cross-sectional analyses, variation in the number of words recalled independent of age was explained largely by non-shared influences (65-72%), with clear additive genetic influences (12-32%), and marginal shared family influences (1-18%). The longitudinal phenotypic analysis of the word recall task showed systematic linear declines over age, but several nonlinear models with more dramatic changes at later ages, improved the overall fit. A two-part spline model for the longitudinal twin data with an optimal turning point at age 74 led to: (a) a separation of non-shared environmental influences and transient measurement error (~50%); (b) strong additive genetic components of this latent curve (~44% at age 60) with increases (over 50%) up to age 74, but with no additional genetic variation after age 74; (c) the smaller influences of shared family environment (~15% at age 74) were constant over all ages; (d) non-shared effects play an important role over most of the life-span but diminish after age 74.
McArdle
John J
JJ
University of Southern California, Los Angeles, CA, USA.
Plassman
Brenda L
BL
D000368:Aged; D000375:Aging; D001699:Biometry / Q000379:methods*; D003430:Cross-Sectional Studies; D004200:Diseases in Twins / Q000235:genetics; D006801:Humans; D008297:Male; D008569:Memory Disorders / Q000235:genetics*; D008875:Middle Aged; D008957:Models, Genetic; D015999:Multivariate Analysis; D010641:Phenotype; D012042:Registries; D013997:Time Factors; D014427:Twins