What is the Relationship Between Autism Spectrum Disorders and Intellectual Disability?

My four-year-old child is diagnosed with autism spectrum disorder (ASD). His evaluator said that my son was “intellectually disabled in addition to having autism.” What is the relationship between autism spectrum disorders and intellectual disability? Is my son also intellectually disabled?

Answered by
Leanne Tull, M.ADS, BCBA
and
Bobby Newman, PhD, BCBA-D
Room to Grow
ASAT Past-President and Advisory Board Member

This can be a very sensitive subject, and the response you get can vary depending on the professional you ask. Before answering your question, it is important to highlight diagnostic labels that have changed since the debut of the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). Two notable name changes, specific to the diagnoses you mention in your question, are:

1. Intellectual Disability: previous editions of the DSM used the term mental retardation. The shift to Intellectual Disability marked a major milestone of efforts to solidify the use of a term that has been commonly used by behavioral, medical, and educational professionals, including advocacy groups, for the past two decades. Mental retardation replaced obsolete terms such as feeblemindedness, moron, and imbecile; now, over fifty years later, the term ‘mental retardation’ is being eliminated for similar reasons (Harris, 2013).

2. Autism spectrum disorders (ASD): previous editions of the DSM referred to ASDs as Pervasive Developmental Disorder, a “diagnostic umbrella,” with five subtypes: 1) Autistic Disorder; 2) Asperger’s Disorder; 3) Rett’s Disorder; 4) Childhood Disintegrative Disorder; and 5) Pervasive Developmental Disorder-NOS (“Not-Otherwise-Specified”). ASD is a label that now reflects a scientific consensus that the five previously separate disorders are actually a single condition with different levels of symptom severity. However, it is important to note that a previous diagnosis of any of the five ASD subtypes was grandfathered into the DSM-5 ASD diagnosis. Individuals with any of these diagnoses do not lose them and at this time do not need to be re-evaluated under the new criteria (APA, 2013a; 2013b).

Your child may have some degree of intellectual disability; some areas of ability may be normal, while others (i.e., cognitive functioning and language abilities) may be weak. To expand on this further, consider the criteria for the diagnosis of intellectual disability. According to the DSM-5, there are three criteria for intellectual disability:

  1. Deficits in intellectual functioning, confirmed by both clinical assessment and individualized, standardized testing;
  2. Significant adaptive living skill deficits; and
  3. Onset of intellectual and adaptive deficits during the developmental period (APA 2013a; 2013c).

Furthermore, adaptive living skill deficits involve three domains, or areas. These domains determine how well an individual copes with everyday tasks:

  1. The conceptual domain includes skills in language, reading, writing, math, reasoning, knowledge, and memory;
  2. The social domain refers to empathy, social judgment, interpersonal communication, the ability to make and retain friendships, and
  3. The practical domain centers on self-management in areas such as personal care, job responsibilities, money management, recreation, and organizing school and work tasks (APA, 2013a; 2013c).

Does your child meet these three criteria including demonstrated impairments in the adaptive functioning domains? Many individuals diagnosed with ASD, showing symptoms during the developmental period, are also diagnosed with an intellectual disability. A central question, however, is whether your child’s measured intellectual deficit is a reflection of deficits in all adaptive functioning domains. For example, a child with ASD may do well on tasks related to visual-perceptual skills (such as completing a jigsaw puzzle) but may not do as well on social problem-solving tasks (such as empathy or perspective taking). Some children with ASD (such as those formerly diagnosed with Asperger’s syndrome) often have average or above-average language skills and do not show delays in cognitive ability or speech.

Limitations in intellectual functioning are generally thought to be present if an individual has an IQ (intellectual quotient) test score of 70 or below, approximately two standard deviations below their expected IQ compared to same-age-peers (APA, 2013c). If you consider the requirements of standardized intelligence tests, the general focus is on how the individual is required to interact with the tester, answer questions, follow directions, imitate, and receptively or expressively identify requested items. Many individuals diagnosed with ASD have simply not learned these skills at the time of testing and may demonstrate challenging behavior in contexts in which demands are being placed upon them. Following effective programming, IQ may increase by dozens of points (e.g., Lovaas, 1987). However, increased IQ scores do raise some concern. For instance, did intervention increase the individual’s intelligence, or help the individual to develop the skills that allowed them to successfully participate in the test? To account for this gap in testing validity, the new diagnostic criteria for intellectual disability place emphasis on both clinical judgment and standardized intelligence testing; and less emphasis is placed on the IQ score, there is no longer a “cut-off” score or threshold.

To illustrate the rationale for this change, consider the following personal anecdote: A colleague of Bobby Newman was reading a story to Newman from a magazine about a celebrity actor. At one point, the colleague realized Newman was looking at her blankly and said, “you have no idea who I’m talking about, do you?” Newman did not; he couldn’t identify 98% of the celebrities currently in the limelight – it’s just not his area of interest.

Why mention this anecdote? Consider that many students diagnosed with ASD are not exposed to various life experiences that provide the knowledge necessary to answer questions on IQ tests. Scaled IQ scores represent approximations of conceptual functioning; however, they may be insufficient to assess reasoning in real-life situations and mastery of practical tasks within conceptual, social, and practical domains.

To consider the question with respect to your son, more information is needed. What type of testing was administered? Did the test have verbal and nonverbal components? Was there a large spread among the subtests’ scores? Was it a test appropriate for someone of his age? Was the test ever standardized with people with disabilities? Was the test conducted properly? Was the test conducted by someone with whom your son was familiar with, and in a familiar setting, was the test done in such a way that he was comfortable or motivated?

Was there a measure of adaptive behavior collected? Adaptive behavior measures are often assessments that do not directly test the individual, but rather interview significant others to compare the behavior to age-standardized norms. If so, was there a spread among subscales’ scores? A large spread, particularly with some subscales in or around the normal range, would argue against an intellectual disability label. Finally, was adaptive behavior testing completed properly? Tests should not be conducted by mailing the questionnaire to parents; this is a completely inappropriate use of such measures.

The best course of action at present is to understand the diagnostic criteria improvements in the DSM -5. Mental retardation had long been divided into mild, moderate, severe, or profound levels of severity. The DSM-5 highlights the need to use both clinical assessment and standardized testing of intelligence when diagnosing intellectual disability. The severity of impairment is now based on adaptive functioning rather than IQ test scores alone; specifiers, instead of subtypes, are used to designate the extent of adaptive dysfunction in academic, social, and practical domains (Harris, 2013). Consider your child’s intellectual disability diagnostic label as an artifact of continuing language, interactive, or other skill deficits, as opposed to some inherent and global intellectual delay.

Approach the “high-functioning” and “low functioning” ASD labels with caution; given the specific and scattered nature of skills and deficits displayed by individuals diagnosed with ASD, it often makes little sense. Higher and lower functioning in what areas? Criteria that surround these labels do not speak to the specific challenges of each child, and may actually undermine the effort that many individuals on the spectrum put forth each day.

The late, great Stephen Jay Gould 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. This publication may provide useful background when further considering your question.

References:

American Psychiatric Association (2013a). Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition. Arlington, VA: American Psychiatric Association.

American Psychiatric Association (2013b). Autism Spectrum Disorders (Retrieved 28.08.15), from http://www.dsm5.org.

American Psychiatric Association (2013c). DSM-5 Intellectual Disability Fact Sheet (Retrieved 16.09.15), from http://www.dsm5.org.

American Psychiatric Association (2013d). Highlights of Changes from DSM-IV-TR to DSM-5 (Retrieved 22.09.15), from http://www.dsm5.org.

Gould, S. J. (1981). The Mismeasure of Man. New York: Norton.

Harris, J. C. (2013). New Terminology for Mental Retardation in DSM-5 and ICD-11. Current Opinion in Psychiatry, 26(3), 260-262.

Lovaas, I. O. (1987). Behavioral treatment and normal educational and intellectual functioning in young autistic children. Journal of Consulting and Clinical Psychology, 55(1), 3-9.

Cite this:

Tull, L. & Newman, B. (2009). Clinical corner: What is the relationship between autism spectrum disorders and intellectual disability? Science in Autism Treatment, 13(1), 3-6.