Genetic influences and infantile autism [13]

In his original description of infantile autism, Kanner suggested an 'inborn defect', because symptoms were often present from early infancy. Despite the rarity of a family history of autism and lack of an increase in parental consanguinity, there are two reasons for suspecting hereditary influences: the 2% rate of autism in siblings is 50 times that of the general population and a family history of speech delay is found in about a quarter of families. Reports of single pairs of twins with autism have not added much to our knowledge of genetic effects because of a bias toward reporting monozygotic (MZ) concordant pairs and because few reports contain both adequate clinical descriptions and evidence of zygosity. The authors undertook a study of a systematically collected sample of 21 pairs of same sexed twins, one or both of whom had autism as diagnosed by the criteria of Kanner and Rutter. The results reported here indicate the importance of hereditary influences in the aetiology of autism.