Am.erican Journal of Medical Genetics 39:148-154 (1991) Estimating Genetic Influences on the Age-at- Menarche: A Survival Analysis Approach

A, survival analysis regression model is de-scribed for analyzing twip. data on the age-at-menarche. The model includes latent genetic and environmental covariates and allows one to test hypotheses regarding the nature of fa-milial aggregation for age-at-onset. Addi-tionally, the model accommodates a variety of baseline survival distributions and therefore may be used to test different developmental hypotheses. Model-fitting results indicate that a survival model with a baseline gamma distribution gives an adequate fit to recalled age-at-menarche of 1,888 pairs of Australian female monozygotic and dizygotic twins. Fur-ther, results show that additive genetic and dominance genetic effects contribute to shared variation in age-at-menarche. If there are common environmental influences on the timing of menarche, they are completely ob-scured by nonadditivity in genetic factors, and information from other relationships would be required to detect their effect. KEY WORDS: twins, gamma distribution, correlated ages-of-onse