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Almost exactly three years ago, I suggested as much, based on evidence pointing in that direction:

Several decades after the introduction of autism as a diagnosis, researchers have reported that professionals are still engaging in “diagnostic substitution”: moving people from one diagnostic category, such as “mental retardation” or “language impairment,” to the autism category. For instance, in one recent study, researchers at UCLA re-examined a population of 489 children who’d been living in Utah in the 1980s. Their first results, reported in 1990, identified 108 kids in the study population who received a classification of “challenged” (what we consider today to be “intellectually disabled”) but who were not diagnosed as autistic. When the investigators went back and applied today’s autism diagnostic criteria to the same 108 children, they found that 64 of them would have received an autism diagnosis today, along with their diagnosis of intellectual disability.

Further evidence of this shift comes from developmental neuropsychologist Dorothy Bishop and colleagues, who completed a study involving re-evaluation of adults who’d been identified in childhood as having a developmental language disorder rather than autism. Using two diagnostic tools to evaluate them today, Bishops’ group found that a fifth of these adults met the criteria for an autism spectrum diagnosis when they previously had not been recognized as autistic.

This latest study, by Santhosh Girirajan and colleagues at Penn, evaluated special education enrollment data for 6.2 million children. Although the numbers remained pretty stable for 11 years, the diagnostic categories shifted around, with the increase in autism diagnoses almost completely balancing a decrease in the numbers of students categorized as intellectually disabled. At least two thirds of the numbers were attributable to this shift.

The numbers also depended on age. The older age groups had a higher rate of shifted diagnoses compared to younger groups, so changing categories explained about 59% of the increase among autistic 8-year-olds but almost 97% of it among 15-year-olds.

As I’ve noted, diagnostic shift is one factor in the recent prevalence increases. The other factor, as research highlights, is increased awareness, which means more diagnostic capture. A Danish study from earlier this year, covering more than 600,000 children, reached similar conclusions. The data triangulate on these factors as playing a huge role in autism diagnosis prevalence–and its variation. As I wrote last year at SFARI.org:

Variations in awareness may also underlie the differences in numbers from state to state. One reason for this, experts say, is the wide variability in the resources available for diagnosing and serving children in different communities.

For example, New Jersey, which has the highest reported prevalence, is known for providing extensive services for people with autism, notes Rebecca Landa, director of the Center for Autism and Related Disorders at Kennedy Krieger Institute in Baltimore, who was not involved in the study. “There’s a lot of awareness among professionals in that state,” she says.

In contrast, in largely rural states such as Alabama, “we don’t know how much the media is penetrating into small communities; we don’t know what kinds of hardships families in some of these communities are having,” she says.

What’s more, intellectual disability is more common in black and Hispanic children with autism than in white children with the disorder, suggesting that children in these groups with milder symptoms may be going undiagnosed.

That’s a “troubling” possibility, says (Craig) Newschaffer (director of the A.J. Drexel Autism Institute in Philadelphia). “Children with autism and intellectual disability tend to be diagnosed at earlier ages, so this suggests that the gap in diagnosis across ethnic groups may be even wider.”

Research bears out this concern, as I noted this week in a response to a highly problematic article by Robert F. Kennedy Jr. about autism in African-American children.

Much ink, many bits and bytes, and an enormous amount of money and emotional energy have been spent on the search for why autism prevalence has increased so steeply. After a decade of studies, the research continues to close in on diagnostic shift and enhanced awareness as playing a comprehensive, almost all-encompassing role in this trend. With this recognition, the next step should be a concurrent shift in all of that energy and funding toward resources and support for autistic people.

(Source: forbes.com)

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