Severe mental retardation in a Swedish county. II. Etiologic and pathogenetic aspects of children born 1959--1970.

In an unselected series of 122 children born in 1959--1970 with severe mental retardation (SMR), the magnitude and distribution of the different etiologic and pathogenetic factors were analysed. Prenatal causes were considered relevant in 73 per cent, perinatal in 10 and postnatal in 3. In 12 per cent no traceable cause whatsoever was found. Infantile primary psychoses constituted 2 per cent. Within the prenatal group, no less than 43 per cent presented firm evidence favouring a genetic etiology, chromosomal syndromes together constituting 36 per cent and mutant gene disorders 7 per cent. Etiologically unclassifiable cases with prenatal stigmata and congenital defects amounted to 18 per cent. A condition of fetal deprivation of supply was considered to have been of major importance in 8 per cent. Almost half of the cases had one or more associated CNS handicaps. Cerebral palsy syndromes were evident in 18 per cent and epilepsies in 30 per cent. The relative risk of having cerebral palsy in addition to SMR was strongly correlated to cases classified as prenatally or perinatally acquired CNS syndromes. It is concluded that prenatal prevention is of special importance for reducing the occurrence of SMR. As chromosomal aberrations are the cause in more than 1/3 of cases with SMR, the desirability of developing effective cytogenetic screening methods and programs applicable to all pregnant women is particularly emphasized.