Genetic and environmental effects on mortality before age 70 years

There is a familial influence on risk of many diseases and on mortality in general, which, according to studies of twins, is due to a combination of genetic and environmental effects. Adoption studies, which rest on different assumptions, may also be used to estimate separately the genetic and environmental effects on rate of dying.

The genetic influence on the rate of dying before age 70 years was investigated by estimation of the associations in total and cause-specific mortality of Danish adoptees and their biologic full and half siblings. Familial environmental influences shared at the same time in life were investigated in adoptees and their adoptive siblings. The study basis is the 14,425 nonfamilial adoptions formally granted in Denmark during the period 1924 through 1947, recorded in the Danish Adoption Register. From this register we selected the 1552 "case" adoptees (who died before 01 April 1993) and 1710 "noncase" adoptees alive at that date. The siblings of the case and noncase adoptees were traced in the archives and followed forward, and the rates of dying before age 70 years were compared.

Compared with mortality of the biologic siblings of noncase adoptees, the mortality of biologic siblings of dead adoptees was approximately 2-fold higher for death with infections and vascular causes, and around 45% increased for natural causes and for all causes.

The results suggest that there is a genetic effect on the rate of death with infections, vascular causes, natural causes and all causes, whereas there is no indication of an influence of shared sibling environment.