Average or high IQ in ASD higher than thought

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The number of individuals who have autism spectrum disorders (ASD) without intellectual impairment is higher than previously believed, according to recent research.

Maja Katusic and colleagues examined the medical and school records of more than 30,000 individuals born between 1976 and 2000 in Olmsted County, Minnesota. They identified cases of ASD based on behavioral data in the records, using both broad and narrow definitions of autism as defined by the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSMIV). In addition, they identified individuals with documented clinical autism diagnoses.


The researchers found that of 890 individuals who met the inclusive definition of autism and had IQ scores available, 59 percent had an average or higher IQ score. Of the 453 individuals who met the narrow criteria, 51 percent had an average or higher IQ score. Only 43 percent of the 187 individuals with a clinical diagnosis of ASD had an average or higher IQ score. Males were more likely than females to have average or higher IQs.

The researchers say their findings “suggest that nearly half of individuals with ASD have average or higher IQ,” and warn that these individuals “remain at risk for not being identified.”

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“IQ in autism spectrum disorder: a population-based birth cohort study,” Maja Z. Katusic, Scott M. Myers, Amy L. Weaver, and Robert G. Voigt, Pediatrics, November 4, 2021 (online ahead of print publication). Address: Maja Katusic, Mayo Clinic, 200 1st St SW Rochester, MN 55902, [email protected].

—and—

“Autism without intellectual impairments more common than previously reported,” Jonathan Moens, Spectrum News, December 1, 2021.

This article originally appeared in Autism Research Review International, Vol. 36, No. 1, 2022

IQ in Autism Spectrum Disorder: A Population-Based Birth Cohort Study
Maja Z. Katusic, MD; Scott M. Myers, MD; Amy L. Weaver, MS; Robert G. Voigt, MD
Address Correspondence to Dr Maja Katusic Mayo Clinic 200 1st St SW Rochester, MN 55902. E-mail: [email protected]

Pediatrics (2021) 148 (6): e2020049899.
https://doi.org/10.1542/peds.2020-049899

OBJECTIVES
We aimed to describe the intellectual ability and ratio of boys to girls with average or higher IQ within autism spectrum disorder (ASD) cases identified in a population-based birth cohort. We hypothesized that research-identified individuals with ASD would be more likely to have average or higher IQ, compared to clinically diagnosed ASD. We also hypothesized the male to female ratio would decrease as the definition of ASD broadened.

METHODS
ASD incident cases were identified from 31 220 subjects in a population-based birth cohort. Research-defined autism spectrum disorder, inclusive criteria (ASD-RI) was based on Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision, autistic disorder (AD), Asperger Disorder, and pervasive developmental disorder not otherwise specified criteria. Research-defined autism spectrum disorder, narrow criteria (ASD-RN) was a narrower definition based on Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision AD criteria. Clinical diagnoses of ASD were abstracted from medical and school records. Intellectual ability was based on the last IQ score or on documented diagnoses of intellectual disability if no scores available. Average or higher IQ was defined as IQ ≥86.

RESULTS
A total of 59.1% of those with ASD-RI (n = 890), 51.2% of those with ASD-RN (n = 453), and 42.8% of those with clinically diagnosed autism spectrum disorder (n = 187) had average or higher IQ. Within the ASD-RI and ASD-RN groups, boys were more likely than girls to have an average or higher IQ (62.0% vs 51.3% [P = .004] and 54.1% vs. 42.5% [P = .03], respectively).

CONCLUSION
Our data suggest that nearly half of individuals with ASD have average or higher IQ. Boys with ASD are more likely to have average or higher IQ than girls. Patients with ASD and higher IQ remain at risk for not being identified.

Wouldn't their conclusion also be approximately correct for neurotypical people?

The above article's conclusion that roughly half of the autistic population has average or above-average intelligence is a departure from the controlling theories of autism, which have presumed below-average IQ in more than half of the autistic population.