Minor malformations in mental retardation of various aetiology.

The frequency of minor malformations was determined in 246 mentally retarded children with an I. Q. ranging from 37 to 67. According to the probable aetiology, the patients were divided into 4 groups: Down syndrome (n = 29), other genetic causes (n = 22), perinatal and postnatal environmental damages (n = 68), and unknown aetiology (n = 127). One thousand consecutive newborn infants served as controls. The mean number of minor malformations per subject was the highest in patients with Down syndrome (3.38) and other genetic disorders (2.00). It was significantly lower in the mentally handicapped of unknown (0.88) and of environmental origin (0.37). The number of multiple minor anomalies was high in the genetically determined conditions and the smallest and nearing the control value in the exogenic group. The results support the idea that the presence of minor malformations, and especially of multiple ones, refers to the prenatal onset of mental deficiency.