Increasing diagnoses of autism, most notably in multi centre research in the USA, (Centers for Disease Control and Prevention, 2012) has underpinned belief in an autism epidemic. If the increase is valid – meaning a true increase in cases and not just in case recognition – the implications are profound and urgent for identifying causes likely to be novel and potentially controllable (www.nimh.nih.gov/about/director/index.shtml). The most important recent evidence against the autism epidemic hypothesis is a 2011 British adult general population survey showing no significant difference in prevalence by age (Brugha et al, 2011). However to date this finding from a community survey of over 7000 adults able to take part in a health survey has not been replicated. As part of an extension of the 2011 survey (Brugha et al, 2012) adults with intellectual disability were studied and the association of autism with age was examined.
As part of a prevalence survey of autism in an epidemiological study of adults with intellectual disability unable to take part in a general population health survey, to examine further the association of autism with age.
Sampling was based on population case registers of adults with intellectual disability in three parts of England. Adults were living in institutions (communal care establishments) or in private households (excluding anyone able to participate in a health survey interview). Phenotyping was primarily based on the age appropriate module of the ADOS (modules 1 and 4) in phase one of a two phase survey design in which a stratified subsample were also assessed with the ADI-R and DISCO.
A total of 290 interviews were conducted with intellectually disabled adults. 89 autism cases were identified. Analyses are being undertaken examining the association of autism with age and other factors and possible confounders, with work on the interpretation of findings still ongoing.
Challenges to the interpretation of findings include reduced survival in this population, constraints on autism assessment in the most profoundly intellectually impaired adults and issues of statistical power. Further work in the general population is also planned.
1. Brugha, T., Cooper, S. A., McManus, S., et al (2012) Estimating the Prevalence of Autism Spectrum Conditions in Adults: Extending the 2007 Adult Psychiatric Morbidity Survey. (ed C. a. M. H. T. The NHS Information Centre), pp. 31. Leeds: The NHS Information Centre.
2. Brugha, T. S., McManus, S., Bankart, J., et al (2011) Epidemiology of autism spectrum disorders in adults in the community in England. Archives of General Psychiatry, 68, 459-466.
3. Centers for Disease Control and Prevention (2012) Prevalence of Autism Spectrum Disorders — Autism and Developmental Disabilities Monitoring Network, 14 Sites, United States, 2008. (ed Centers for Disease Control and Prevention), pp. 19. Atlanta: Centers for Disease Control and Prevention.
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