Study on the Prevalence Rate of Pervasive Developmental Disorder in Yokohama City


Yokohama National University, Faculty of Education and Human Sciences, Department of Disability Studies

We studied persons with pervasive developmental disorder who are older than 18 years old and visited the Social Welfare Center for Disabilities of Yokohama City between April 2003 and March 2005.
At the Social Welfare Center, 84 males and 13 females, totaling 97 people, were diagnosed as having autistic disorder, based on DSM-IV\a ratio of 6.5:1, male: female. Among these, 68 males and 10 females, totaling 78 people, had IQs of 75 or less, that is were with mental retardation, according to the results of the Tanaka-Binet test, which shows that the rate of so-called high function autistic disorder not accompanied by mental retardation is 19.6 %. This matches the statement in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition issued by the American Psychiatric Association1), in which it was found that 75% of autistic disorder cases are accompanied by mental retardation.

Next to be mentioned is the prevalence rate of pervasive developmental disorder which includes autistic disorders and Asperger syndrome. Our study on Yokohama City reports that the prevalence rate of mental retardation is 0.74% of the population2) and that people with pervasive developmental disorder account for 16.2% of those with mental retardation3). When calculated based on these results, people with autistic disorder accompanied by mental retardation account for 0.12% of the population. Also, when 78 people with pervasive developmental disorder accompanied by mental retardation, 19 people with autistic disorder not accompanied by mental retardation, so-called high function autistic disorder, and 7 cases of Asperger's syndrome are totaled, the prevalence rate of pervasive developmental disorder is 0.16%. (Asperger's syndrome was only seen in males and was not accompanied by mental retardation). This shows that pervasive developmental disorder occurs in 16 of every 10,000 people. (If Asperger syndrome is not taken into consideration, 15 of every 10,000 people). This nearly meets the results of Wingfs study4), which concluded that 21.2 of every 10,000 people have pervasive developmental disorder, as well as those of Gillbergfs study reports in 19865). Our study is based on requests from people with mental retardation or pervasive developmental disorder and their families in order to obtain support for public welfare service. As, in some cases, people with these disorders might not make this request, our study results might show numbers which are slightly smaller than the actual numbers.

According to our study, only one in 10,000 people is diagnosed as having Asperger's syndrome; however, as reported by Gillberg et al., later in 1993, 36 out of 10,000 people are with Asperserfs syndrome, and 56 out of 10,000 people have pervasive developmental disorder6) when the 20 out of 10,000 people with autistic disorder are taken into account. There is a huge discrepancy between these results and our own. Yokohama City has a long history of medical diagnoses and in creating public welfare support plans for mental retardation (including autistic disorder with mental retardation); however, such policies for those who are older than 18 years old with high function autistic disorder or with Aspergerfs syndrome just started in April, 2001, according to the municipal bylaws. Since few people with Aspergerfs syndrome have demanded public welfare support, Yokohama City needs to further develop medical diagnoses and a welfare support system, and compare them with the study results of Gillberg, etc. for examination.


1)the American Psychiatric Association: Diasgnostic and Statistical Manual of Mental Disorders, Fourth Edition. 1994.
2)Yoshida, A., Sugano. T., Matsuishi.M.: Mental Retardation Incidence in Yokohama City. Journal of Disability and Medico-Pedagogy. Vol.5.16-17. 2002.
3)Yoshida, A., Sugano, T., Matsuishi, T., Endo, K., Yamada. Y.: A Study on Complications of Mental Retardation, Journla of Disability and Medico-pedagogy, Vol.15.6-8, 2007
4)Wing, L.and Gould, J.: Severe impaiments of social interaction and associated abnormalities in children: epidemiological and classification. Journal of Autism and Childhood Schizophrenia, Vol.9. 11-29.1979.
5)Gillberg, C., Persson, E., Grufman, M. and Themner, U.: Psychiatric disorders in mildly and severely mental retarded urban children and adlescents: epidemiological aspects. Journal of Child Psychology and Psychiatry, 12,131-144, 1986
6)Ehlers, S. and Gillberg, C.: The epidemilologyof Asperger syndrome: A total population study. Journal of Child Psychologyand Psychiatry, 34, 1327-1350,1993.
(originally published on Journal of disability and medico-pedagogy, Vol.16.2007.p.1-2.)