Objective: To estimate the prevalence of autism, to assess the strength of its association with specific medical disorders, and to test for a secular increase in its incidence.
Method: An epidemiological survey was conducted among 325,347 French children born between 1976 and 1985 and living in three different French départements. Diagnosis, educational level, and associated medical conditions were abstracted from the records of children known to local educational authorities. Data were also pooled with those from another similar survey.
Results: One hundred seventy-four children (mean age: 11.6 years) with autism were identified. The prevalence rate was 5.35/10,000 (16.3/10,000 if other pervasive developmental disorders are included), with no difference according to geographical area or social class. Rates of medical conditions were as follows: 1.1% for tuberous sclerosis, 2.9% for chromosomal abnormalities including fragile X, 2.9% for cerebral palsy, 4.6% for sensory impairments, 0.6% for neurofibromatosis, 0.6% for congenital rubella, and 1.7% for Down syndrome. In the combined sample of 328 children with autism, the level and pattern of medical correlates were comparable, with tuberous sclerosis having a consistently strong association with autism. Prevalence rates were similar in successive birth cohorts.
Conclusion: Medical disorders (excluding epilepsy and sensory impairments) accounted for fewer than 10% of the cases of autism. No secular increase in the prevalence of autism was found.