The epidemiological study of autism in Fukushima-ken.

A survey of children aged under 18 years in Fukushima-ken (prefecture) in Japan showed that 2.33 per 10,000 children suffered from early infantile autism. The average of prevalence rates of autistic children born between 1968 and 1974 was 4.96 per 10,000 children. Based on a comparison between cities and rural districts, the prevalence rates of the former were significantly higher than those of the latter. Autistic boys outnumbered autistic girls with a sex ratio of 9 : 1. Psychiatric illnesses were very rare among the relatives of autistic children. The rate of prenatal and perinatal complications was higher than the national norm among autistic children. Parents of autistic children had a significantly higher education than the national norm. There were more nuclear families in the autistic group than in the national norm.