“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 CMAJ

This 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 (p<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). In 2006, of all children with an ASD for whom testing documentation was available, 41% had cognitive impairment. When modern criteria are applied, children identified are less likely to test as having general cognitive impairments, and unusual learning profiles indicating scatter in cognitive skills rather than across-the-board cognitive delays might be more salient indicators of an ASD than intellectual impairment (35).”

In an earlier post, I covered the latest findings regarding ID and autism:

Yeargin-Allsopp et al. (2003) write: “Children with autism were identified as part of the Centers for Disease Control and Prevention’s (CDC) Metropolitan Atlanta Developmental Disabilities Surveillance Program (MADDSP), an ongoing, active population-based surveillance program to monitor the occurrence of 5 DDs (autism, cerebral palsy, hearing loss, mental retardation [MR], and vision impairment) among 3- to 10-year-old children in the 5-county metropolitan Atlanta area.25-26 The total number of 3- to 10-year-old children residing in metropolitan Atlanta in 1996 was 289 456 (51% male; 58% white, 38% black, and 4% other racial group).”

According to Yeargin-Allsopp et al. (2003), “Psychometric data were available for 880 (89%) of the 987 children with autism. Of these, 676 (77%) had been administered a standardized intelligence test, and the others had received a developmental test (a list of psychometric tests is available from the authors). Children with a full-scale IQ of 70 or less or a score of 2 or more standard deviations below the mean on the cognitive domain of a developmental test were classified as having a cognitive impairment.”

So what did Yeargin-Allsopp et al.find?: “Among the children with autism (N = 987), 62% had at least 1 coexisting MADDSP-defined disability or epilepsy. Of the children with an IQ or developmental test result (N = 880), 68% had cognitive impairment (64% based on IQ data alone). Among children with psychometric test data (N = 880), 20% had mild MR, 11% moderate MR, 7% severe MR, 3% profound MR, and 28% with an unspecified level of cognitive impairment that included 9% classified as MR-NOS using IQ data and 19% classified using developmental scores (Table 2). In addition, of the children with autism, 8% had epilepsy, 5% had cerebral palsy, 1% had vision impairment, and 1% had hearing loss. We found that as the severity of MR increased the sex ratio decreased (4.4 to 1.3), indicating a greater proportion of females in the severe and profound levels of impairment (Table 2).”

In other words, about two-thirds had a cognitive impairment, but of those most were mild cases, not severe. Standardized IQ tests for autistic individuals have potential problems; it can be tremendously difficult to ascertain capability from a noncompliant individual. In addition, since language deficits are part of the autism triad, the verbal portion can be expected to be lower than nonautistic peers, and it does not appear that the nonverbal IQ test is always (or often administered) in place of the traditionally used IQ test. Where noncompliance, lack of inherent interest, difficulty with communication, and discomfort with strangers can all get in the way of a reliable test result, IQ tests must be taken with a grain of salt, especially where performance outside the testing arena demonstrates more competency than the IQ score would have predicted.

Individuals with autism are likely to have additional diagnoses, as well: “Many children (70%) we identified with autism had more than 1 diagnostic evaluation, and 61% (data not shown) were seen at more than 1 educational or medical program in the community, thus providing independent information on the behaviors used to determine case status.”

Scientists aren’t in agreement with an 80% rate of ID in autistic individuals. In fact, the findings show that only 7% of those with autism are severely intellectually disabled. The overwhelming majority who have ID have mild to moderate ID. Many individuals with mild ID are able to live independent lives. Having autism comorbid with ID makes full independence more challenging, but it is the autism that creates this impediment, not the ID.

The portrait of autism has changed over the last forty years. More mildly affected individuals are being diagnosed with autism spectrum disorders as our awareness and understanding of autism has grown.

Most of those diagnosed with autism are not severely disabled. That doesn’t mean that severely impaired individuals who require 24/7 care shouldn’t be acknowledged and recognized. But restricting autism to this minority isn’t going to happen.

Like it or not, our understanding of autism has broadened to include those on the broader autism phenotype who have less significant barriers. Personally, as the mother of three children who have tremendous commonalities with each other despite the variation in severity of the autism and the variation in intellectual impairment (my son has an intellectual disability but my daughters give every indication of being gifted), I respect and appreciate the increased awareness. Individuals who are extremely bright may still face significant challenges and have impairments that impede their ability to live independently.

Trying to manipulate numbers to fit one’s notion of autism as also being intellectual disability is not scientifically accurate, and the historical numbers of 70% or so were based not on sound science and replication, but on taking a few original studies and their interpretation of 70% and carrying it forward in time rather than measuring the IQ of the study participants. In other words, it was a readily accepted and rarely questioned axiom that ID and autism went hand-in-hand. Assessing the IQ in noncompliant individuals (as many autistic individuals can be) is a difficult enterprise, so previous studies’ assessments were used.

Times have changed, though, as our awareness and willingness to question have increased. Scientists now assess IQ. Recognition that traditional IQ testing may not best assess capability has also grown. Remember, IQ as assessed by the WAIS-III and Stanford-Binet assess the likelihood of success at academic performance. If a person hasn’t had the kind of instruction or exposure to those kinds of material, he will not score well. It doesn’t tell us about functional life skills. It doesn’t tell us about the ability to hold a job, live semi-independently, socialize appropriately.

These changes in how we view and assess autism are good things. Whether the APA gets their act together and manages to put together a severity scale that is useful without pejorativeness is another matter entirely, as is the willingness of interested members of the autism community to accept communally drawn definitions of autism based on the scientific research.

As to Harold Doherty’s use of  the Canadian Psychological Association as a source for the 80%, yes, they do give that figure: “Cognitive impairment is present in about 80% of persons diagnosed with Autism and general intellectual functioning is most often below average. Persons diagnosed with Asperger’s Disorder have average to above average intellectual functioning.”

The problem with this is that it is not substantiated and the literature assessing ID and autism clearly doesn’t back this up. It’d be like using Autism Speaks to back up the 80% divorce rate, something they still spread around despite the evidence to the contrary. We should always be wary of generalizations not backed by scientific studies that provide the data to make those generalizations.

The Canadian Psychological Association’s references for that briefing are not reputable scientific articles:

“Autism Society Canada (2006). Focus on Change: An Open Letter From Autism Society Canada.

Autism Society Canada (2006). Largest Collective Voice of the Autism Community in Canada Calls on Government to Take Steps to Establish a National Autism Strategy.

Bryson, S. (2003). Autistic Spectrum Disorders: Recent Findings on Prevalence, Etiology and Neuropsychopathology. Canadian Psychological Association Preconvention Workshop.
Hamilton, Ontario.

Jack, M and Ady, J. (2006). A Guide to Choosing Interventions for Children with Autism Spectrum Disorders. Alberta Centre for Child, Family and Community Research.

Perry, A. and Condillac R. (2003). Evidence-Based Practices for Children and Adolescents
with Autism Spectrum Disorders. Review of the Literature and Practice Guide. Children’s
Mental Health Ontario.”

It’s shoddy work, at best, and not backed up with hard data.

Wiggens et al. (2009) examined autistic regression and intellectual disability. Wiggens et al. (2009) note that “questions regarding the number of children with an ASD who experience regression, the mean age at which regression occurs, and whether developmental delays exist prior to the loss of skills remain unanswered” (p. 360). To try to get to some answers, Wiggens et al.”analyzed data from a comprehensive, population-based surveillance program at the Centers for Disease Control and Prevention (CDC) that systematically gathers and records behavioral and diagnostic information on children who display characteristics associated with ASDs” (p. 360).

For their study, Wiggens et al. looked at MADDSP ASD surveillance records: “Of the 285 children who met ASD surveillance case status, 49 (17%) had developmental regression documented in surveillance records. Of the children who met the ASD case status and had a previously documented ASD,26 percent had documented developmental regression. Forty-four of the children who met ASD surveillance case status and had document regression were boys, yielding a male:female ratio of 8.8:1.0.Age at time of regression was available for 45 participants.The mean age at time of regression was 28.2 months (median 24.0 months; mode 24.0months), although there was considerable variation about the mean (SD 18.9 months; range 1–91 months)” (p. 364).

When they compared these two groups (regression version nonregression), here’s what they found:

“Children with an ASD with documented regression showed significantly more general developmental concerns at or before 36 months of age than did children with an ASD without documented regression…than children with an ASD without a documented loss of skills” (p. 365).

In addition, “Children with an ASD with documented regression were also significantly more likely than those without documented regression to have cognitive impairment” (p. 365). Of those with documented regression, 29 percent scored “average or above average cognitive skills” while 38 percent of those who did not undergo regression scored average or above. Wiggens et al. note that “children with an ASD with documented regression were rated by clinician reviewers as being more impaired than children with an ASDwithout a documented loss of skills” (p. 366).

The question of cognitive impairment and levels of functionality come up alot on the blogs, forums, and various threads. In this study, which looked at population data: “Of the 268 children who had cognitive test data available in surveillance records, 40 percent scored in the range of cognitive impairment (IQ ≤ 70), and 60 percent were not cognitively impaired. Fifty percent of children in the sample were rated by clinician reviewers as moderately impaired, 29 percent were rated as mildly impaired, and 21 percent were rated as severely impaired” (p. 364). Contrary to certain individuals insistence that the rate of cognitive impairment is 80 percent or so, this study which actually looked at the data gathered by the “Metropolitan Atlanta Developmental Disabilities Surveillance Program (MADDSP) at the CDC” found a rate of 40 percent. And they only found 21 percent being severely impaired, also contrary to what AoAers would have you believe.

In their discussion, Wiggens et al. write:

“Using a population-based surveillance cohort, we found that the percentage of children with autistic regression ranged from 17 percent among children who met ASD surveillance definitions, to 26 percent among children who met ASD surveillance definitions and had recognized ASD documented in surveillance records. Our estimates are in line with those from previous studies (Rutter and Lord, 1987; Siperstein and Volkmar, 2004)and suggest that autistic regression is more likely to be noted when a child has a clearly documented ASD diagnosis. This pattern may explain why higher prevalence rates for autistic regression are found in studies that use clinically referred samples (Davidovitch et al., 2000) and implies that any loss of social or language skills is an important ‘red flag’ for ASDs (Filipek et al., 2000). Furthermore, children in our sample who experienced autistic regression were more likely to have cognitive impairment and were rated as significantly more impaired by clinician reviewers.These results, coupled with the finding that the male:female ratio increases more than 50 percent in autistic regression (Bernabei et al., 2007), lend credence to the idea that autistic regression is related to severity of disability and is much more likely to occur in boys than in girls” (p. 369).

Plenty of recent studies look at intellectual disability and autism. Consistency in data, though, on intellectual disabilities is highly variable.

Amiet et al. (2008), in their study looking at epilepsy, autism and intellectual disability that “like epilepsy, intellectual disability is still considered to be intrinsically associated with autism, although there is a trend toward reporting less than 50% of ID in autistic subjects in recent studies” citing Dawson et al.’s (2007) study on autistic intellgence. Amiet et al. found that there was a connection between intellectual disability and increased epilepsy rates: “The pooled prevalence of epilepsy was 21.4% in autistic subjects with ID (n = 1485) versus 8% in autistic subjects without ID (n = 627).”

Mandell et al. (2009) looked at ethnic differences concerning autism, and also examined intellectual disability:  “Black children were most likely and children of “other” race/ ethnicity were least likely to have an IQ lower than 70 documented in their records.” Mandell et al. found that 33% overall had IQs below 70, but in 25% of their sample, IQ scores were not available.

Yeargin-Allsopp (2008) examined the ALSPAC cohort for autism prevalence and found a rather low number for intellectual disability: 14.7%, but notes that “more severely affected children may have been under ascertained.”

Fombonne (2002), in looking at epidemiological trends in the pervasive developmental disorders, notes a wide range of IQ scores. Consistency in IQ trends isn’t to be found if you look at a large enough pool of studies.

Chakrabarti and Fombonne (2001) found in a sample of 97 individuals with a pervasive developmental disorder: “A total of 97 children (79.4% male) were confirmed to have a PDD. The prevalence of PDDs was estimated to be 62.6(95% confidence interval, 50.8-76.3) per 10 000 children.Prevalences were 16.8 per 10 000 for autistic disorder and 45.8 per 10 000 for other PDDs. The mean age at diagnosis was 41 months, and 81% were originally referred by health visitors (nurse specialists). Of the 97 children with a PDD, 25.8% had some degree of mental retardation and 9.3% had an associatedmedical condition.”

According to Chakrabarti and Fombonne (2001),  Only a third of the sample had “no functional use of language.” A fourth of the sample had “some degree of mental retardation.”

Not surprisingly, a “significant difference was found for the presence or absence of mental retardation between the 3 PDD subtypes (22 = 40.6;P<.001), the AD group having more frequent and severe cognitive delays than the Asperger syndrome and PDD-NOS groups.”

There are folks in the autism community that insist there’s an epidemic and we’re fixing to be hit with a tidal wave of nonverbal, diapered adults, but this does not seem to be the case:

“In our survey, AD accounted for only 27% of the cases with these children showing much greater cognitive and language impairments. By contrast, the majority of cases was found at the mild end of the autistic spectrum, with the PDD-NOS and Asperger syndrome groups accounting for 71.1% of the cases. High proportions of PDDs were also found in recent surveys (46.8%18 and 40%19). Prior surveys focused on a narrow definition, which led to the exclusion of these milder forms although it has been recognized for some time that they represented a group as sizable if not bigger than that of autism.5 The inclusion of these milder variants certainly may account for a substantial part of the increase in prevalence rates.”

Contrary to this fantastical and fanatical assumption that most individuals with autism are severely disabled, incapable of speech, etc., the reality appears to be that a loosening in diagnostic criteria that allows for the diagnosing of many more individuals with less severe impairments had occurred. Now, this study’s been out there for nine years. I’ve said before, and I’ll say it again here, research is poorly disseminated to the public. I’ll go a step further, here, and say that is almost as poorly disseminated to the clinicians and practitioners who diagnose and treat autism. These discrepancies between what researchers know and what practitioners, clinicians, parents, and the public know are widening, not lessening. This is frightening, and undoubtedly accounts for all manner of misinformation and woo to abound.

A new study, recently out and getting a lot of media attention, is by by Berkel et al. (2010). Berkel et al. found “de novo copy number variations in the SHANK2 synaptic scaffolding gene in two unrelated individuals with autism-spectrum disorder (ASD) and mental retardation.” Berkel et al. then looked at “SHANK2 in 396 individuals with ASD, 184 individuals with mental retardation and 659 unaffected individuals.” In the abstract (study not readily available), the authors conclude, that there are “common genes between ASD and intellectual disability.”

The question of gene variants and the connection between autism and intellectual disability is not new, despite some individuals’ attempts to co-opt new research to bolster their arguments regarding the rate of intellectual disability and autism co-morbidity. Research into genetic variants reveals commonalities between autism and intellectual disability, although the reasons for the variation in expression and severity are not clear. Two examples of gene variant studies follow.

In 2009, Y. Qiao et al. looked at benign copy number variants in individuals with autism and individuals with intellectual disability, and they found “147 distinct bCNVs in 221 subjects with idiopathic ID and/or ASD.” However, further analysis showed: “ bCNVs in individuals with idiopathic ASDs and IDs showed that the number of bCNVs/subject and frequencies of most bCNVs were not significantly different from controls when the same array platform was used.”

In 2004, Laumonnier et al. found that “NLGN4 deficiency in the brain may lead to abnormal development of synaptic structures and may have dramatic effects on communication processes and cognitive development.”

There is much that is not understood regarding autism, intellectual disability, and other neurodevelopmental disorders. Research findings provide tantalizing glimpses, but often do not provide a cohesive portrait, and wading through media hype to get to the actual research findings can be a tedious and unrewarding task, especially when one finally arrives and realizes that the media and social organizations have provided an inaccurate look at the research.

Round numbers and clear, concise statements like the one the Canadian Psychological Association offered regarding autism and intellectual disability may soothe the worried soul, may provide a bedrock, but like the aggressive assertions of parents who believe they saw their child develop autism after an adverse vaccine reaction (“I saw the light go out in his eyes”), it is a false island of security that provides no benefit.


Berkel, S., Marshall, C., Weiss, B., Howe, J., Roeth, R., Moog, U., et al. (2010). Mutations in the SHANK2 synaptic scaffolding gene in autism spectrum disorder and mental retardation. Nature Genetics42(6), 489-491. doi:10.1038/ng.589.

Chakrabarti S, Fombonne E (2001). “Pervasive developmental disorders in preschool children”JAMA 285 (24): 3093–9. doi:10.1001/jama.285.24.3093. PMID 11427137. http://jama.ama-assn.org/cgi/content/full/285/24/3093.

E. (2002). Epidemiological trends in rates of autism, Mol Psychiatry (Suppl 7), 4–6.

Laumonnier, F., Bonnet-Brilhault, F., Gomot, M., Blanc, R., David, A., Moizard, M., et al. (2004). X-Linked Mental Retardation and Autism Are Associated with a Mutation in the NLGN4 Gene, a Member of the Neuroligin Family. American Journal of Human Genetics74(3), 552-557. Retrieved from Academic Search Complete database.

Mandell, D., Wiggins, L., Carpenter, L., Daniels, J., DiGuiseppi, C., Durkin, M., et al. (2009). Racial/ethnic disparities in the identification of children with autism spectrum disorders. American Journal Of Public Health99(3), 493-498. Retrieved from MEDLINE database.

Wiggins, L., Rice, C.,&Baio, J. (2009). Developmental regression in children with an autism spectrum disorder identified by a population-based surveillance system. Autism: The International Journal of Research&Practice13(4), 357-374. doi:10.1177/1362361309105662.

Yeargin-Allsopp, M. (2008). The prevalence and characteristics of autism spectrum disorders in the ALSPAC cohort.Developmental Medicine And Child Neurology50(9), 646. Retrieved from MEDLINE database.

Yeargin-Allsopp, M., Rice, C., Karapurkar, T., Doernberg, N., Boyle, C., & Murphy, C. (2003). Prevalence of Autism in a US Metropolitan Area. JAMA: Journal of the American Medical Association, 289(1), 49. Retrieved from Academic Search Complete database.

Y., Q., Harvard, C., Riendeau, N., Fawcett, C., X., L., Holden, J., et al. (2009). Putatively benign copy number variants in subjects with idiopathic autism spectrum disorder and/or intellectual disability. Cytogenetic & Genome Research,123(1-4), 79-87. doi:10.1159/000184694.