Mild mental retardation in Swedish school children. II. Etiologic and pathogenetic aspects.

The etiology and pathogenesis of mild mental retardation (MMR) (IQ 50--70) were analysed in an unselected series of 91 Swedish school children with this condition born 1966--70. The cause was considered to be prenatal in 23%, including 5% genetic, prenatal unknown in 10% and alcohol fetopathy in 8%. A perinatal cause--mainly asphyxia combined with fetal deprivation--was found in 18% and a postnatal in 2%. In 55% the cause was untraceable. Half of these latter children had close relatives with below-average intelligence. Exceptionally low birth weights and lengths were revealed among the 8% with alcohol fetopathy. Neurological abnormalities were found in 43% of the children, epilepsy in 12%, cerebral palsy in 9% and a clumsy child syndrome in 23%. Psychiatric disturbances were present in 31%.--The types and multitudes of predisposing background factors in MMR were compared with those in severe mental retardation and with those in the IQ group 71--75. The general conclusion is drawn that in Swedish school children negative pre- and perinatal factors are today responsible for a larger proportion of MMR than has previously been known.