Pathogenic factors in idiopathic mental retardation.

Pathogenic factors in a mentally retarded population were evaluated by comparing their frequency among three groups of patients: a control group with predominantly genetic retardation and consanguineous parents; a group with severe idiopathic retardation and unrelated parents; and a group with mild idiopathic retardation and unrelated parents. Seven factors were found to be significantly more common among the patients with idiopathic retardation than in the genetic control group: a history of maternal reproductive inefficiency; bleeding during pregnancy; toxemia during pregnancy; signs of perinatal stress; neonatal anoxia; neonatal jaundice; and seizures during the first year of life. A history of repeated maternal abortions was particularly associated with mild retardation, and infantile seizures were particularly associated with severe retardation. The latter association remained significant even after exclusion of all infantile spasms, neonatal seizures and symptomatic seizures. Since the control group in this study was composed mainly of genetically retarded patients, the associations observed seem likely to be related to the causes of retardation rather than simply being the effects of a damaged fetus.