Severe mental retardation in Swedish children born 1959-1970: epidemiological panorama and causative factors.

The findings from two recent Swedish retrospective studies on severely mentally retarded children born 1959-70 are surveyed. One study concerned an average county--Uppsala--in the middle of Sweden, the other a vast northern county, Västerbotten, with a sparse population. Figures for incidence and prevalence are given, as well as the percentage distribution of aetiological/pathogenic groups and subgroups, and the frequency of multihandicaps. Prenatal causes were apparent in about 70% of affected children, Down syndrome being the main condition (32%). A background of mutant genes in severe mental retardation was found significantly more often in Västerbotten than in Uppsala (17% and 7% respectively). Perinatal causes were revealed in 10 and 8% (9% of the two series pooled together) and postnatal causes in only 3 and 1% (2%). Associated CNS handicaps were present in about half of the children (42% in Uppsala and 52% in Västerbotten), with epilepsy in 30 and 36%, cerebral palsy in 18% and 19%, and a combination of epilepsy and cerebral palsy in 8 and 16%, respectively.