Why do many children with ASD have an Intellectual Disability?

Irases by Ray David

Artwork courtesy of Ray David

by Dr Giacomo Vivanti

Many individuals with Autism Spectrum Disorder (ASD) have Intellectual Disability (that is, below average I.Q. and poor adaptive functioning). What is the nature of this association? Data published from a recent study at the Olga Tennison Autism Research Centre (OTARC), Intellectual development in autism spectrum disorders, provide new insight into this complex issue.

The scientific community has given little attention to this question for decades. Indeed, the prevalent view in the field is that Intellectual Disability in ASD is an additional, unrelated condition that ‘happens’ to be present in some individuals with ASD, and is not seen as providing valuable information on the nature of autism.

Following this line of thought, most research in ASD conducted over the past decades, including research on treatment, has excluded individuals with ASD who have an Intellectual Disability, on the ground that their Intellectual Disability would confound the interpretation of results. As a consequence, we don’t have much knowledge on effective treatments for children with lower IQ (arguably the ones that are more in need of help) and we don’t know much about why Intellectual Disability occurs so often in ASD.

However, the data published in our study provide some new insight into this complex issue. Results from a longitudinal analysis of the intellectual development of 80 children with ASD indicate that the risk of developing an Intellectual Disability increases with the severity of ASD symptoms. In other words, those children who are more severely affected by ASD in early development are more likely to have a lower I.Q. later in life.

Child by Ray David

Why is this the case?

Recent research on brain plasticity indicates that brain organization in typical development is critically shaped by the child’s social learning experiences during early development. We propose that the presence of severe symptoms of ASD impedes this process, so that children who are more severely affected are those who are least able to appropriately engage in the social learning experiences that are crucial for normal intellectual development. Therefore, ASD and Intellectual Disability do not appear to be unrelated conditions. Rather, the presence of severe ASD symptoms might be a risk factor for developing Intellectual Disability. That is, the children with “ASD associated with Intellectual Disability” are in fact children whose ASD symptoms are so severe that these preclude them from processing the environmental inputs that ‘sculpt’ brain organization during early critical periods.

From this perspective, we argue that the practice of excluding children with Intellectual Disability in ASD research to study “pure autism unconfounded by Intellectual Disability” is ill considered. Rather, research should target those factors that place affected individuals at an increased risk of negative outcomes, such as the presence of an Intellectual Disability, and understanding the underlying causal mechanisms, to inform clinical practice, with the ultimate goal of fostering positive outcomes for all individuals with ASD.

Hat by Ray David

How to read and download the article

The article Intellectual development in autism spectrum disorders has been made available without cost to you. When you click through to the extract, the top right hand side column provides numerous formats including PDF and full text.

20 Responses to "Why do many children with ASD have an Intellectual Disability?"

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  1. Autistic

    July 13, 2013 at 7:41 pm

    “Many individuals with Autism Spectrum Disorder (ASD) have Intellectual Disability (that is, below average I.Q. and poor adaptive functioning).”

    Many black people have committed murders. But that tells us very little about the average black person, even though the nasty stereotype is brought up many times.

    Many Autistics have become clued in that a good proportion of the scientists interested in them are third-rate. This is another example.

    • Wojciech Nadachowski

      July 16, 2013 at 1:28 pm

      We remain unconvinced at the appropriateness of the analogy used here.

      At OTARC we believe that individuals with ASD and lower IQ and those with ASD and higher IQ deserve the same respect and research attention. Our research is devoted to improve outcomes of all individuals with ASD, irrespective to their IQ.

  2. cedra

    July 23, 2013 at 4:27 pm

    It’s great to read researchers are finally looking into this question. It is one I am frequently asked and not one I am able to answer!

  3. Joel

    September 4, 2013 at 3:17 am

    I’d be very very wary of interpreting any results linking ASD and intellectual disability. There is plenty of evidence suggesting that increased severity of ASD symptoms correlates with HIGHER intellectual ability, but a decreased ability to communicate it with the neurotypicals who typically design and run these studies. Forgive the analogy but tests of animal intelligence frequently grossly undermeasure because they are designed by humans to test how humans think animals think. That is often a very far cry from the way the test subjects actually think.

    To the extent that a study like this helps improve understanding of ASD, how to provide reasonable accommodations so a brilliant Aspie with communication deficits can be a productive member of the workforce, etc., great. But if the takeaway is that people with ASD by and large are intellectually defective, and the more ASD they show, the more defective they are, that is at best an enormous oversimplification, and at worst a cruel and malicious misinterpretation of the facts of ASD and neurodiversity.

    • Lisbeth Wilks

      September 5, 2013 at 9:55 am

      The term ‘intellectual disability’ in science is purely descriptive and it is not loaded with the negative connotations you suggest. It refers to learning difficulties that affect adaptive behaviour. Our aim is to understand why many individuals with autism have difficulties that affect their ability to learn important skills (e.g. self-help) and to live an adult independent life without the need for care and assistance. Our mission as researchers is to try to understand the causes of these poor outcomes, so that we can change this state of things and help all individuals with ASD (not just ‘brilliant Aspies’ but also severely impaired individuals) achieving their full potential. – Dr Giacomo Vivanti

      • Joel

        September 16, 2013 at 4:56 am

        Thank you for your response. I appreciate the clarification. I just get very concerned about the (unintentional) biases that often cause different ways of thinking and communicating from being recorded as deficits in studies that are blind to the fact they are measuring square pegs on a test designed for round ones.

        It does sound like you are defining “intellectual disability” as referring to social/adaptive skills in the context of neurotypical society, not raw intellectual capacity of individuals with ASD. I’m still not wild about the terminology, as it can easily be misinterpreted (the way I appear to have done), but I appreciate what you’re actually trying to accomplish and wish you luck in your research.

  4. usethebrainsgodgiveyou

    September 4, 2013 at 10:34 am

    I read your paper. I will admit I am a housewife, and have no right to enter the discussion. My degree was in Special Education, what would now be considered Intellectual Disabilities. My interest in Autism came about when my son was given a label of “educational autism” by the school. (Medically, Semantic-Pragmatic Language Disorder, PDD-NOS among others.)

    I’m not sure I misread the piece, I tried to do it carefully but science is still much of an enigma to me, even though I’ve been reading studies for 16 years since my son’s diagnosis. I appreciate what you are trying to say here, and it is VERY IMPORTANT to see autism as a continuum, and not as “pure” with co-occurring disabilities of ID, Epilepsy, Apraxia, ADHD, Dyslexia, or any other “add on”. Personally, when working with autistic children (I also taught 2 years) I tried to “guess” which children had ID, which is global, or equally distributed in all areas of measured intelligence…and autism, which may lead to giant discrepancies between high and low areas, more of a “scatter” in testing results. One student, not my own, had an age equivilant of 11 years in language comprehension, and yet an A.E. of 18 months in adaptive behavior based on the Vineland. Blew me away…how does that happen? My own son scattered from the 1st to the 9th stanine in testing.


    I noticed two things that made me go, “hmm…” There’s no need to answer as I know you are busy. First of all, toddlers who had been caught up in a developmental sweep would probably be more severely afflicted with autism to begin with and parental concern would lead them to look for answers earlier. (Believe me, we “know”, even if we can’t quite put our finger on it..) More severe autism would discourage gains compared to those children whose parents were less concerned in the two year period following that atypical early diagnosis.(I had NO IDEA they were diagnosing kids that young! It used to be they delayed diagnosis until after age 3. I probably got that mixed up or didn’t understand. )

    There was one more thing…(I also have Alzheimers, just kidding…kind of)

    Oh, yes…a comment about intervention and increase in IQ score. I think this is a questionable correlation, and I will try to explain why. I only have my own example as reference. A “case study of one”, ha! IQ scores, with the exception that I can think of The Peabody Picture Vocabulary Test–are exceedingly language related (The Sally-Anne test, anyone?Anyone?) There is an intelligence not measured in language, like the Raven Progressive Matrix’s test, that autistics beat the pants off of controls. So, IQ is not necessarily language related.This is my intro and then I’ll tell you about Ben.

    I worked with Ben, ages 3-4 two hours a day for a year. (500+ hours of professional intervention). I presented language to him visually (using PEC’s) and kinesthetically. Even so, at age 4, after my “intervention”, he underwent testing, the WISC I believe, and scored an overall IQ of 79. Three years later, while still speaking echolaically in grade 2, he scored a 99. In third grade, testing showed his IQ to be 116. In preparing for accommodations for college, it was 100. He was upset that he was normal, we both were expecting it to be much higher. Still, his dycalculia put him in the second stanine for calculations, his verbal IQ was 126 (I think the 9th.) Yet it was nearly exactly the same profile as the earliest test, of 79. That’s a fluid number,what does it really measure? You see this so often, the scatter highs and lows, in LD kids. It used to be an indicator of LD (Learning Disabilities).

    Autism, in part, is a language disorder. Initially, children can be expected to make giant gains in IQ as they pick up language. I do agree with Dawson, et al, regarding the Early Start Denver Model. I wonder how much I helped my own child using the _language curriculum_ of Catherine Maurices “Early Intervention for Young Children with Autism”? (I didn’t use the behavioral aspects, ie, sit in your chair, do this…….but the language only.) I would like to believe I helped my son gain IQ points through presenting language early and comprehensively. But did I change his basic development? Children of average or above IQ with autism have grown to lead fulfilling lives without it, haven’t they?.

    One thought your study did bring to mind…There is such a thing as acquired autism, like the children who grow up in orphanages. It would be interesting to do a comparison of the two types,, acquired via environment, and genetic/biological autism.

    • Lisbeth Wilks

      September 5, 2013 at 9:56 am

      Thank for the comment. We do agree that intelligence is a complex construct, and definitely it involves more than language. However, many individuals with ASD, although not all of them, have difficulties in non-verbal cognitive domains as well. The main issue is that whatever instruments we use to measure intelligence, we consistently see in literature that lower cognitive abilities are related to poorer outcomes. There is also evidence that early intervention improves cognitive outcomes in children with ASD, so we do think is possible to positively affect intellectual development through intervention, though more research is needed to investigate what works for whom, and why. For information on ‘acquired autism’ versus biological autism, please refer to the studies of Michael Rutter and colleagues (e.g., Rutter et al., 2007, Rutter et al., 2001). – Dr Giacomo Vivanti

  5. usethebrainsgodgiveyou

    September 4, 2013 at 11:32 pm

    I regret the last line of this. It seems that some studies have been done on romanian orphans, and it’s ethics are questioned. http://www.aeonmagazine.com/world-views/can-research-on-romanian-orphans-be-ethical/

  6. Mancell Cornish

    October 2, 2013 at 9:39 pm

    I’m curious to know how this information has been gathered. My son is severely autistic & so far non verbal, though he is only 3. We paid $1500 for a proper psychological evaluation by a reputable group (who’s clients are mostly kids on the spectrum) ,using standard assessment techniques.
    We were told his intelligence level is in the bottom1-5% of the population. I was disappointed to find data collection relied heavily on verbal communication. Some of the tests he received a zero score because of his limited language skills. At the time I wondered if a child speaking a foreign language would have faired as badly.
    I don’t deny he has massive problems & he is far from typical, but he shows me in many ways that cogs are turning inside his little head, particularly when it comes to problem solving & using an iPad.
    ASD kids are never going to preform well in typical testing situations.

  7. Hannah Louis

    October 3, 2013 at 5:31 am

    I think it is important to remember that by definition IQ is a hypothetical construct, ie. it asks a series of standardized questions and makes an inference about thought processes based upon what the subject is able to communicate and the speed with which they can communicate. The IQ test is an indirect measure focusing on behavior that may not be of social significance . It is well established that evidence based interventions for ASD are behavioural and use direct measures of behavior of social significance to individuals. This approach is evidence based regardless of the result of an IQ test.

    The use of IQ tests on children with social and communication disorders is controversial. IQ tests are regarded as “high stakes” testing because of their potentially negative consequences for learning opportunity. Unfortunately circular reasoning around IQ tests is common in psychology and education i.e. “we know Johnny has an intellectual disability because he could not answer the questions on the IQ test. He could not answer the questions on the IQ test because he has intellectual disability” From a natural science perspective, IQ tests are an explanatory fiction. Evaluations of individual learning potential should not be made without a critical evaluation of learning goals and programs. Best practice for ASD is ongoing systematic evaluation using criterion referenced tests. IQ tests may (or may not) be helpful to establish service eligibility.

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  15. Klas Wullt

    November 10, 2016 at 11:08 am

    Emotional nonsense and retarded experts and psychologists and hysteric ignorant people!
    Under these new rules I am an adult with Autism Spectrum Disorder
    and I am highly intellectual. You fail to understand that there is a difference between retarded intellectually damaged autists and non-retarded highly intellectual autists.
    Psychologists never gathered enough solid scientific data on Aspergers Syndrom
    it was always misunderstood and therefore it doesn’t exist.
    The retarded autists can never transition into highly functioning Aspergers
    with some sort of training or terapy. The scope and function of the disability
    is completly different. The retarded autists have severe inability
    to interact with reality itself and understanding the existence of other people
    the way a normal person or a person with aspergers can.
    Highly functioning people with outdated aspergers
    doesn’t have less autism, they have a different autism.
    I can think, I am sentient, I am even more sentient than normal.
    My brain is abnormally wired for pattern seeking and I understand
    that people exist and reality exists.
    Retarded Austists have severe problems functioning so they don’t
    have any pattern seeking ability or their pattern seeking ability
    only apply to one thing.
    Yes we all have this inability to read faces and read humans
    but a person with aspergers can learn to read people
    People with aspergers have flawed and strange speech and language skills
    but it’s a language skill. We are just stuck with a painful
    and lonely sense of objective knowledge, unable to communicate
    and share our through or being part of others lives.
    Being unable to adapt to society doesn’t mean I am stupid,
    but it doesn’t cause the retardation either.
    Rather some sort of damage or genetic superiority
    affects different parts of the brain.
    My pet theory is that like dogs, Aspergers have been breed by society to be better than Autists, let me explain! Autism creates an all or nothing situation.
    Minor biological changes or other abilities in combination with Autism
    either leads to solipsism and retardation or highly desirable intellectual abilities.
    Aspergers creates many qualities in me that normal people admire
    and has made me a very popular person though I am unable to use them
    be part of the world of other people.
    My ability to learn anything that has some intellectual element is fantastic
    but I can’t adjust to society to develop my talent nor can I use my abilities
    in a profession. No, grammar is not my special interest.
    People with Aspergers have an antisocial learning ability which allows
    us perceive information objective like a human computer.
    Normal people have an pedagogic intelligence based on imitation learning.
    If you don’t have this ability the autist child can’t develop a concept of reality
    or a concept of self. Autism serves as a quality checking mechanism, the environment for survival of the fitters.
    In order to develop into a normal functioning human being
    the autist has to be more intelligent than the average person.
    I have no intuitive abilities, I have no spontaneous unplanned emotions.
    I am entirely like a computer, bad programming goes in and bad shit goes out.
    Everything in my life is intellectual and also terrible chaotic.

    I have meet plenty of retarded austist and high functioning autists in my life.
    You are putting us through hell and many of these new an a trendy theories
    are way behind of what knowledge many adults with Asperger
    has to painfully spend their lives learning.
    You are invalidating our life knowledge and experience because you
    are only investigating underdeveloped people and only look at the subjective value of peoples
    weaknesses and not the patterns of peoples weaknesses.

  16. L Morris

    March 30, 2017 at 11:11 am

    As a mum of two boys with Autism & both have an intellectual disability. They are smarter than they are on paper. The report is the opposite of their abilities, however the report is a good indication on where the children need extra help or resources.
    My eldest (17) has an IQ of 70 but yet at high school is achieving very high results because of how he is being taught.


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