Half of the variation in susceptibility to mortality is genetic: findings from Swedish twin survival data.

Molecular epidemiological studies confirm tremendous variability in genetic and environmental susceptibility to disease and death for humans. This variability as well as the roles of genetic and environmental factors in susceptibility to death can be estimated in the analysis of survival data on related individuals (e.g., twins). In this paper, correlated gamma-frailty models are applied to survival data on Swedish twins to estimate genetic parameters in six models of susceptibility. It is shown that the frailty model with additive genetic and nonshared environmental components fits the data best. The estimate of narrow-sense heritability in gamma frailty is about 50%. The results of genetic analysis confirm our earlier findings from the studies of Danish twins that about 50% of individual susceptibility approximated by gamma-distributed frailty is heritable.