Identification and Diagnosis of Autism Spectrum Disorders: An Update

Greg Pasco


Pediatr Health. 2010;4(1):107-114. 

In This Article

Definitions of Autism Spectrum Disorder

The most authoritative and widely acknowledged definitions of the diagnostic criteria for ASDs are detailed in both the text revision of the Diagnostic and Statistical Manual of Mental Disorders 4th Edition (DSM-IV-TR)[4] and the 10th Revision of the International Classification of Diseases (ICD-10).[5] These criteria have evolved through previous versions of both classification systems and whilst there are small differences between them they have certain key features in common. First, there is a requirement for difficulties to be manifested in three main areas – communication; social interaction; and restricted, repetitive or stereotyped behaviors – the so-called 'triad of impairments'. Second, there is a distinction between 'core' (or 'classic') autism and variants of autism where not all of the main features of autism are present (e.g., pervasive developmental disorder – not otherwise specified [PDD-NOS] and atypical autism). Third, Asperger syndrome is defined as a separate disorder. Even though sensory abnormalities are experienced by the majority of individuals with ASDs,[6] sensory deficits are not currently incorporated into the diagnostic criteria. A summary of the characteristics of the different categories of ASDs are detailed in Box 1.

In clinical settings, classic autism is generally diagnosed by 3 years of age,[7] and in some cases as early as 2 years.[8] Asperger syndrome is typically diagnosed much later, often after children have started school.[7] The term 'pervasive developmental disorders' is not widely known and children meeting the criteria for the variants of autism are typically diagnosed using the term 'autism spectrum disorder',[9] which is also often used as an umbrella term to include classic autism. Asperger syndrome was included in DSM-IV and ICD-10 owing to recognition of the heterogeneity of symptoms within ASDs as well as a need for subtyping in order to facilitate research into the genetic basis of autism.[10] However, the formal diagnostic definitions are very restrictive and few individuals actually meet the criteria for Asperger syndrome, often because they also meet the criteria for one of the other pervasive developmental disorders.[11] It is not possible to reliably differentiate Asperger syndrome from autism or PDD-NOS using the formal diagnostic criteria.[10] Consequently, many clinicians do not refer to the DSM and ICD criteria in relation to Asperger syndrome, and there is still no absolute consensus on how Asperger syndrome should be defined.[11]

There has been increasing interest among researchers in the broader autism phenotype (BAP), mostly in relation to the relatives of individuals with ASDs.[12,13] Early evidence suggests that the younger siblings of children with ASDs demonstrate a number of characteristic skills and difficulties associated with autism, particularly during the early years,[14,15] although it is unlikely that BAP will become a formally defined clinical diagnostic category.


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