What is the relationship between autism and mental retardation?

Bobby Newman, PhD, BCBA

Question: My four year old child is diagnosed with PDD. A recent evaluator recently said that my son was “retarded in addition to being autistic.” What is the relationship between autism spectrum disorders and mental retardation? Is my son also retarded?

Answer: This can be a very touchy subject, and the answer you get can vary by the professional you ask. Please understand that my answer reflects my own bias and understanding of the clinical literature on this issue, and I would need a great deal of information regarding your child to give you an answer that was specific to your child.

That disclaimer out of the way, in a nutshell, my opinion is that it is entirely possible that your child may be functioning in the mentally retarded range, without being truly retarded. To expand on what I mean, consider the criteria for the diagnosis of mental retardation. According to the DSM-IV TR, there are three criteria for mental retardation:

  1. IQ measured to be two standard deviations or more below the mean.
  2. Significant adaptive living skill deficits.
  3. Onset before age 18 (in other words, before development is considered to be completed).

Does your child meet these three criteria? A great many students diagnosed with autism spectrum disorders (ASD) do. My central question, however, is whether this measured intellectual deficit is merely a reflection of current behavioral, communicative, and social difficulties. Consider the requirements of standard intelligence tests: They generally require the student to interact with the tester, answer questions, follow directions, imitate, and receptively or expressively identify requested items. Many students diagnosed with autism have simply not learned these skills at the time of testing. Following effective programming, IQ may jump by dozens of points (e.g., Lovaas, 1987). Did you magically increase the student’s intelligence, or did you help the individual to develop the skills that allowed the child to participate in the test? I would argue for the latter explanation. Just what is intelligence anyway? Is it some general factor, or a collection of specific factors? A person whose name escapes me once said that intelligence is what intelligence tests measure.

Consider another issue: I do some work in Eire, Ireland, and was in the Dublin airport after one of the consulting trips with my friend and colleague Meredith Needelman (a particularly wonderful speech therapist). She was reading a story to me from a magazine about some movie star. At one point, Meredith realized I was looking at her blankly, smiled and said “you have no idea who I’m talking about, do you?” I’m afraid I didn’t. I couldn’t identify 98% of the celebrities out there if you put a gun to my head. It’s just not my area of interest. Call me a cultural illiterate.

Why do I mention this? Consider that many students diagnosed with ASD are not exposed to many life experiences that provide the knowledge necessary to answer questions on the IQ tests. I’m thinking of a student I tested a few years ago. When I first met the student, he was not toilet trained, could not speak, and only consumed Pediasure for nutrition. After a year of very serious effort by staff and family, all of these deficits were ameliorated, and he was able to participate in an IQ test that included a verbal picture identification component. The child labeled a great many items, but missed others I thought he would know. When I went over the results with his mother, I asked if her son had ever seen one of the farm animals on the test. Mom looked at me like I had eight heads, and asked if, considering his former deficits, I thought they were taking him to petting zoos that frequently. The answer was fair enough, but conditions were different now. So I called a bunch of people into the room who were a lot smarter than me (his teacher, speech therapist, and teacher assistants) and we planned a year’s worth of field trips that the family and school would take each week to expose him to missed experiences. We went over a bridge and through a tunnel, to the zoo and an aquarium, to the baseball game, to the ocean, to the forest, and more. I should also mention that on that same intelligence measure, the child scored three standard deviations above the mean on one of the other subtests that did not directly assess expressive language.

To consider the question as regards your son, we need more information. What sort of test was used? Did it have verbal and nonverbal components? Was there a big spread among the subtests? Was it a test appropriate for someone of his age? Was the test ever standardized for people with disabilities? Was the test conducted properly? Was the test conducted by someone with whom the student was familiar, and in a familiar setting, or was the test done in such a way that the student was not comfortable or motivated?

Was there a measure of adaptive behavior collected? These are often assessments that do not directly test the student, but rather interview significant others to compare the child’s behavior to age-standardized norms. If so, was there a spread among subscales? A large spread, particularly with some subscales in or around the normal range, would argue against a mental retardation label. Finally, was the adaptive behavior test done properly? I kid you not, I have heard of such tests being conducted by mailing the questionnaire to parents, a completely inappropriate use of such measures.

I don’t want to be glib, but I think the best course of action at present is to act as though the mental retardation diagnosis is simply an artifact of continuing language, interactive, or other skill deficits (as opposed to some inherent and global intellectual delay). Do not speak “around” your child, as though he was not in the room. He may be understanding a great deal more than you realize. Don’t think he is too delayed for you to attempt to teach particular skills. Make sure you teach necessary prerequisite skills, and then go for it. Students surprise us each day.

The late, great Stephen Jay Gould, an annoyingly brilliant individual, once published a book entitled The Mismeasure of Man. The book describes some of the historical problems with IQ tests and measures of intelligence in general. It’s useful background when considering this question.

Note: This article originally appeared in an issue of Science in Autism Treatment, the newsletter of the Association for Science in Autism Treatment (ASAT). It may not be republished or reprinted without advance permission from ASAT. Email us for reprint permission.

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