An epidemiological study on severe mental retardation among schoolchildren in Bologna, Italy.

The prevalence, causal origin of and impairments associated with severe mental retardation (SMR) were investigated among all school-age children (six to 13 years) living in the city of Bologna, Italy. 90 children (57 boys, 33 girls) with IQs less than or equal to 50 were identified. The prevalence of SMR was 4.2 per 1000 for males, 2.5 per 1000 for females and 3.4 per 1000 for both sexes. Causal origin was prenatal for 33.3 per cent, perinatal for 14.4 per cent, combined pre- and perinatal for 5.6 per cent and postnatal for 13.3 per cent. Another 12.3 per cent of the children with IQs less than or equal to 50 had autism or childhood psychosis, while there was no evident cause of mental retardation for the remaining 21.1 per cent. 50 per cent had at least one associated physical or neurological impairment other than mental retardation, with epilepsy and cerebral palsy predominating.