Some authors, including Peter Szatmari of McMaster University, define ASD as a sort of sub-threshold category, including “terms such as atypical autism, autistic-like, Asperger Syndrome, autistic tendencies, and so forth” but not including autism itself. In his view, there is autism and for those who come close but not quite, there is autism spectrum disorder. However, at Best Behaviour, we use ASD synonymously with the diagnostic category “Pervasive Developmental Disorders” (PDD). PDD includes the 5 diagnoses:
- Asperger’s Syndrome: a type of autism in which the person’s language skills are typical.
- Autism
- Childhood Disintegrative Disorder, which refers to children who develop normally for the first couple few years but who later loose the skills they learned including loss of speech.
- Pervasive Developmental Disorder not otherwise specified (PDD-NOS). This is the “catch-all category for children who present with autistic traits but do not fit into one of the other categories. Often, children diagnosed with PDD-NOS will present with fewer symptoms of autism. Note that the diagnosis is PDD-NOS and not PDD. PDD or pervasive developmental disorder is the larger cluster into which these 5 diagnoses are grouped.
- Rett's Disorder is a genetic disorder affecting girls. It is rare and unfortunately, progressive.
Together, these diagnoses form the autism spectrum. Early intervention may affect each of the conditions on the spectrum differently. For example, Smith, Groen, and Wynn (2000) found that children diagnosed with PDD-NOS made more gains than children diagnosed with autism (note however, that the sample size in this study was small and the study has yet to be replicated and as such, their findings should be read as tentative). According to research by Smith, Klevstrand and Lovaas (1996) and cited again by Smith and Lovaas, 1997, “Girls with Rett's disorder…do not benefit from the treatment" (Smith & Lovaas, 1997, p. 215). Additionally, because children with Asperger’s Syndrome are typically diagnosed later (often around ages 7-8), the impact of early intervention (under the age of 5) hasn’t yet been assessed with this population.
