One of the first studies of its kind has concluded that children with more severe levels of autism spectrum disorder (ASD) are increasingly being excluded from research, a finding, investigators say, that increases the odds that future understanding of the disorder will be incomplete and biased toward the higher-functioning end of the ASD spectrum.
The analysis examined data from 367 studies of children with ASD published from 1991 to 2013. The investigators showed that although close to 90% of studies in the early 1990s included severely affected individuals, the percentage dropped to approximately 30% in the early 2010s, even when the investigators used a liberal definition of autism severity.
Indeed, each passing year included in the analysis was accompanied by a 16% decrease in the likelihood that severely affected patients were included in relevant studies.
"We found this fairly striking because 20 years is not a particularly long time period," principal investigator Matthew Siegel, MD, vice president of medical affairs for the Developmental Disorders Service of Maine Behavioral Healthcare, Portland, told Medscape Medical News. "We also used a very liberal definition of severity, but these were still the findings.
"So it supports the idea that autism research has significantly shifted towards the high-functioning population," Siegel added.
The study was published online December 10 in the Journal of Autism and Developmental Disorders.
Underrepresented Population
Recent years have seen an explosion of research in the field of ASD. In the past 3 decades, there has been a 24-fold increase in the number of articles published on the topic.
Nevertheless, experts have noted that recent literature seems to underrepresent individuals severely affected by ASD. A 2017 query of the National Database for Autism Research revealed that only 11% of study participants with ASD had an IQ <85; even fewer were categorized as minimally verbal.
Specific subsets of patients with ASD have yet to be systematically evaluated across a broad historical range of peer-reviewed publications.
Given the significant role that current research plays in guiding clinical practice, the investigators set out to evaluate the degree to which more severely affected people with ASD have been included in treatment studies. They also sought to assess how such severity is measured and represented.
"We focused specifically on children for whom early treatment experiences are highly influential and therefore are heavily affected by treatment choices," the authors write.
For the current analysis, the investigators used a systematic, multistep approach to search the literature for peer-reviewed, published studies of treatment of children with ASD, excluding single-case reports, from 1991 to 2013.
They assessed representation levels of severely affected populations and examined how severity is defined and represented in the literature by operationalizing it into three domains: communication ability, cognitive functioning, and adaptive functioning.
With respect to cognitive functioning, studies that reported mean IQ scores ≤70 were classified as including severely affected participants. In the communication domain, trials reporting mean scores that fell below the studies' individual cutoffs for communication impairment were coded as having included severely affected participants.
Similarly, studies that reported scores below the trials' specific cutoffs for impaired adaptive functioning were coded as having included severely affected participants.
Studies were classified as being inclusive of severely affected patients if they included individuals who were severely affected in at least one of these three domains. The investigators used metaregression analyses to determine whether trends in average severity over time varied as a function of severity metrics.
Concerning Shift
The final group of studies included 367 articles, 182 of which were randomized controlled trials; the remainder were either uncontrolled trials (n = 100), controlled trials (n = 59), or case series (n = 26). Overall, evidence of inclusion of severely affected patients was found in 186 of the studies (50.7%) when using the researchers' liberal definition of inclusion.
Interestingly, the level of cognitive functioning was the most frequently reported of the three severity domains, appearing in nearly 65.7% of articles. Communication ability was reported in less than half the articles (42.2%), and adaptive functioning was reported in 21.8%. The assessed studies reported only one severity domain 42.8% of the time, two domains 25.3% of the time, and all three 12.3% of the time.
Binary logistic regression revealed that each subsequent year during the study period from 1990 to 2013 was associated with a 16.5% decrease in the likelihood that severely affected children would be included in ASD-treatment studies (odds ratio [OR], 0.84; 95% confidence interval [CI], 0.78 - 0.89; P < .001).
Interestingly, the investigators found that although communication is considered a core deficit in autism, less than half of the studies reported on communication ability. Great variation was found with respect to the measures used in the studies, including communication, intelligence, and adaptive functioning.
The findings highlight the need for greater inclusion of severely affected individuals in autism research, Siegel noted.
"The growth in the autism population over the last couple years is primarily in higher-functioning individuals. Of course, the research should include those people, but it shouldn't shift entirely to that group.
"I worry that perhaps this means that researchers may not be comfortable with the people who are more severely affected by autism. Frankly, it's easier to perform research with higher-functioning individuals," he added.
Shining a Light
Commenting on the findings for Medscape Medical News, Alison Singer, BA, MBA, president of the Autism Science Foundation, who was not involved in the study, said it shines a bright spotlight on a segment of the ASD population that has been pushed into the dark.
"Thanks to this study, we know that higher-functioning people are overrepresented in research," she said. "It makes sense. Higher-functioning people are able to sit still in the fMRI machine; they are able to follow directions more easily; they don't have as many interfering restrictive and repetitive behaviors.
"But the result is that the research on autism is not applicable to people with the most severe forms of autism because they are not included in the studies," Singer added.
"Autism studies must include the most severely affected people with autism. They have the greatest needs. We must find ways to include them, even if it is more challenging," she said.
Siegel added that excluding these individuals could have significant clinical implications.
"What we think and know about autism is what emerges mostly from our research literature," he said. "And if we are increasingly focusing that literature on the highest-functioning population, we're skewing our view of autism for that."
Dr Siegel and Alison Singer have disclosed no relevant financial relationships.
J Autism Dev Disord. Published online December 10, 2018. Full text
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Cite this: Children With Severe Autism Excluded From Research - Medscape - Dec 17, 2018.
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