Years of life lost through Down's syndrome.

A congenital genetic condition does not act either as a cause of death or at the time of death only. Hence, years of life lost through such a conditon cannot be calculated in the same way as for a conventional cause of death. The main difference is that a cause of death acting at age x cuts off as many years of life as the dead person might otherwise have expected to live (life expectancy at age x), whereas a congenital genetic condition exposes an affected person to a different schedule of life-threatening risks from birth onwards. In the latter case, years of life lost is calculated as the difference in life expectancy at birth for affected and non-affected persons. This reasoning is worked out in algebraic form and then applied to Down's syndrome. The data base is provided by two large and recent studies, one in Massachusetts and the other in Denmark, of mortality rates among all cases of Down's syndrome, whether in an institution or not, born during a given period of years or living at a given point in time in a fixed geographical area. So calculated, years of life lost through Down's syndrome relative to the United States general population in 1970 was 53.6 years per 1000 livebirths. Prenatal mortality is also discussed.