Written before the important Nature study by Pinto et al. (2010), this post takes several posts I've done in the past on autism and intellectual disability, as well as responses to an individual who is positing an 80% rate of ID in autistic disorder, and synthesizes them into one large post while hopefully streamlining it some slight bit.Citing Berkel et al. (2010) as proof that ID is present in autistic disorder 80% of the time is not an accurate use of the research by bloggers. Researchers have been examining the connection between genetic variants in intellectual disability and autism for some time now. The latest study, Berkel et al. (2010) offers further corroboration that genetic differences can manifest as a wide variety of phenotypes. What we learn with each additional study is that autism (and as we've known for some time now, intellectual disability) is amazingly complex much of the time.“An overall cognitive deficit is not a defining feature of autism. “ –Amiet et al. (2008)…“Another difference between past and present autism diagnosis involves the presence of intellectual disabilities, adds Yeargin-Allsopp. During the 1960s and 1970s, the vast majority of those diagnosed with autism had an intellectual disability but today, only about 40% have one.” –from CMAJThis does not equate to an 80% figure of ID for those with autistic disorder, no matter how one parses the numbers. In fact Yeargin-Allsop’s 2003 study disconfirms the idea that most individuals with the AD diagnosis have ID. Some individuals are fond of the 80% number for ID and autism comorbidity (like others are so fond of the 80% divorce rate, also untrue).The CDC’s press briefing on the latest autism findings offer this:“Catherine Rice: So in terms of mental retardation, it’s now more commonly referred to as intellectual disability. We know there’s quite an overlap in intellectual disability and autism spectrum disorders. For many years, the best statistics and disorders told us 75% or three-quarters of children with autism also had an intellectual disability. Now the numbers that we’re identifying in our study shows us it’s more about 40% or more specifically 41% of children with autism having an intellectual disability. So overall, this is a population with less intellectual impairment, sometimes referring to as more a higher functional population. So there are many theories out there in terms of this diagnostic shifting and how we look at things or are we really seeing a more high functioning population? That is challenging to sort out.”In 2009, Rice wrote: “Data on cognitive functioning are reported for sites having IQ test scores available on at least 70% of children who met the ASD case definition. The proportion of children with ASDs who had test scores indicating cognitive impairment (IQ ?70) ranged from 29.3% in Colorado to 51.2% in South Carolina (average: 41%). In four of the six sites (Alabama, Arizona, North Carolina, and South Carolina), a higher proportion of females with ASDs had cognitive impairment compared with males (Figure 3), although Arizona was the only site for which the proportions differed significantly (0.05).”In discussing autism and intellectual disability, Rice wrote: “Children identified with an ASD in 2006 reflect a group with less co-occurring cognitive impairment than the population identified ?20 years ago, when autism was conceptualized in a more severe and singular form compared with the spectrum of disorders identified today (2,34...
Dawson, M., Soulieres, I., Ann Gernsbacher, M., & Mottron, L. (2007) The Level and Nature of Autistic Intelligence. Psychological Science, 18(8), 657-662. DOI: 10.1111/j.1467-9280.2007.01954.x The Level and Nature of Autistic Intelligence
Fombonne, E. (2002) Epidemiological trends in rates of autism. Molecular Psychiatry, 7(s2). DOI: 10.1038/sj.mp.4001162 Epidemiological trends in rates of autism
Yeargin-Allsopp, M. (2003) Prevalence of Autism in a US Metropolitan Area. JAMA: The Journal of the American Medical Association, 289(1), 49-55. DOI: 10.1001/jama.289.1.49 Prevalence of Autism in a US Metropolitan Area
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