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Summary A systematic study was made of a representative group of 21 same‐sexed twin pairs (11 MZ and 10 DZ) in which at least one twin showed the syndrome of infantile autism. There was a 36 per cent pair‐wise concordance rate for autism in MZ pairs compared with o per cent concordance in DZ pairs. The concordance for cognitive abnormalities was 82 per cent in MZ pairs and 10 per cent in DZ pairs. It was concluded that there were important hereditary influences concerning a cognitive deficit which included but was not restricted to autism. In 12 out of 17 pairs discordant for autism, the presence of autism was associated with a biological hazard liable to cause brain damage. It was concluded that brain injury in the infancy period may lead to autism on its own or in combination with a genetic predisposition. Uncertainty remains on both the mode of inheritance and exactly what is inherited.
Folstein et al. (Thu,) studied this question.