Mortality of mentally retarded children to 17 years of age assessed in a prospective one-year birth cohort.

Mortality among children with mental retardation (IQ less than 71) and mental subnormality (IQ: 71-85) up to the age of 17 years was studied in the 1966 one-year birth cohort of Northern Finland. The 12,058 liveborn children included 97 children, 8.0 per thousand, with severe mental retardation (IQ less than 50) and 68 children or 5.6 per thousand with mild mental retardation (IQ: 50-70). In addition, there were 162 children or 13.4 per thousand who were mentally subnormal (IQ: 71-85). The death rate among the children with mental retardation was 158 per thousand as compared to 22.6 per thousand among children with normal intelligence and was significantly higher among the mentally retarded of all ages. This is mainly an effect of the very high mortality in children with severe mental retardation, predominantly cases of Down's syndrome. It is concluded that mental retardation per se is not necessarily associated with an increased death rate, but the underlying etiology or additional complicating disorders may predispose the child to infections in particular, these being the leading cause of death among the mentally retarded children studied here.