Biological factors in mild mental retardation.

A group of 434 children with non-syndromic mental retardation was analysed for frequency of recorded prenatal, perinatal and infantile biological disturbances. Mildly retarded individuals for unrelated parentage, both idiopathic and familial, had a strikingly higher prevalence of recorded disturbances than did a control group of retarded individuals with consanguineous parents and of probably genetic aetiology. These disturbances were as frequent among those with mild retardation as among parallel groups with severe retardation. The most significant single disturbance among the mildly retarded was a history of maternal reproductive inefficiency. These findings conflict with the view that mild retardation is predominantly 'cultural-familial' and is not pathological in nature.