Case-control study of genetic and environmental influences on premature death of adult adoptees.

Genetic and environmental influence on risk of premature death in adulthood was investigated by estimating the associations in total and cause-specific mortality of adult Danish adoptees and their biological and adoptive parents. Among all 14,427 nonfamilial adoptions formally granted in Denmark during the period 1923 through 1947, we identified 976 case families in which the adoptee died before a fixed date. As control families, we selected 976 families where the adoptees were alive on that date, and matched to the case adoptees with regard to gender and year and month of birth. The data were viewed as a cohort of case parents and a cohort of control parents, and lifetime distributions in the two cohorts were compared using a Cox regression, stratified with regard to the matching variables: gender and year of birth. In the main analyses, the sample was restricted with regard to birth year of the adoptees, and age of transfer to the adoptive parents, and age at death was restricted to the same range for parents and offspring (25-64 years) in order to consider a symmetric lifetime distribution. This reduces the sample to 459 case families and 738 control families. Various truncations, restrictions, and stratifications were used in order to examine the robustness of the results. The results showed a higher mortality among biological parents who had children dying in the age range 25 through 64 years, and this was significant for death from natural causes, infectious causes, vascular causes, and from all causes combined. There were no significant effects for the adoptive parents. This study supports that there are moderate genetic influences on the risk of dying prematurely in adulthood, and only a small, if any, effect of the family environment.