IN THE SEARCH for etiological consistencies in early infantile autism, hereditary factors have not been considered a salient feature in the clinical picture,1-7 nor have they appeared to be a very promising approach for research. A partial explanation for this is that the parents and the siblings of these children appear remarkably free of major mental illnesses and this fact would not tend to support the presence of genetic factors.
There is, however, an interesting but not fully documented finding that suggests a more prominent role for genetic influences in this illness. There are indications that extremely high concordance rates may exist among those homozygous twins who are afflicted with infantile autism. In 1957 Chapman reported three cases of identical twins, two recorded in the previous literature and one case of his own, who were concordant for early infantile autism.8 Vaillant, in 1963,