Autism and diagnostic substitution: evidence from a study of adults with a history of developmental language disorder Dorothy VM Bishop* DPhil; Andrew JO Whitehouse PhD; Helen J Watt BA; Elizabeth A Line BSc, Department of Experimental Psychology, University of Oxford, Oxford, UK. *Correspondence to first author at Department of Experimental Psychology, University of Oxford, South Parks Road, Oxford OX1 3UD, UK. E-mail: [email protected] DOI: 10.1111/j.1469-8749.2008.02057.x Published online 31st March 2008 Rates of diagnosis of autism have risen since 1980, raising the question of whether some children who previously had other diagnoses are now being diagnosed with autism. We applied contemporary diagnostic criteria for autism to adults with a history of developmental language disorder, to discover whether diagnostic substitution has taken place. A total of 38 adults (aged 15–31y; 31 males, seven females) who had participated in studies of developmental language disorder during childhood were given the Autism Diagnostic Observation Schedule – Generic. Their parents completed the Autism Diagnostic Interview – Revised, which relies largely on symptoms present at age 4 to 5 years to diagnose autism. Eight individuals met criteria for autism on both instruments, and a further four met criteria for milder forms of autistic spectrum disorder. Most individuals with autism had been identified with pragmatic impairments in childhood. Some children who would nowadays be diagnosed unambiguously with autistic disorder had been diagnosed with developmental language disorder in the past. This finding has implications for our understanding of the epidemiology of autism. Rates of diagnosis of autism have risen markedly over the past three decades. 1 According to the ‘autism epidemic’ hypothesis, the rise is genuine, whereas the ‘diagnostic sub- stitution’ hypothesis maintains that the true prevalence of the syndrome is constant but the diagnostic boundaries have broadened, so that more children who would previously have had some other diagnosis are now identified with autism. Specific developmental language disorder is a cate- gory where diagnostic substitution seems plausible, given that: (1) communication problems are a core feature of autism; (2) there has been debate over diagnostic bound- aries between autism and language disorder; and (3) autism is increasingly being recognized in children with normal IQ. 2 We used follow-up data to test the hypothesis that some chil- dren diagnosed with developmental language disorder 5 to 25 years ago would currently be diagnosed with autism. Method PARTICIPANTS Participants were drawn from a pool of children who had taken part in a series of studies of developmental language disorder conducted in the period 1986 to 2003 (see Table I).
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