MONTREAL — Autism has become so overdiagnosed that within five to 10 years there could be almost no difference between groups of people who have been diagnosed with the condition and those who haven’t, a Montreal researcher warns following the publication of a new study.

A new meta-analysis published Wednesday in JAMA Psychiatry that analyzed 11 previous major studies carried out since 1966 found that individuals diagnosed with autism have become progressively less different from the general population.

KatarzynaBialasiewicz via Getty Images A counsellor works with a child diagnosed with autism.

Laurent Mottron, a research psychiatrist at the mental health unit of the Riviere-des-Prairies Hospital and one of the study’s authors, said the gap could soon narrow to nothing.

“Autistic people we test now are less and less different than typical people — really less and less, to the point where if the trend continues, we won’t be able to find the least difference within five or 10 years,” he said in an interview.

Mottron says the problem is that the criteria have lowered to the point where a diagnosis could become nearly meaningless.

Mottron and four other researchers conducted a meta-analysis of previous studies that compared people who have been diagnosed with autism with those who haven’t. The analysis, which included data from 27,723 individuals, includes practically “the whole of planetary research on the autistic brain,” Mottron said.

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The analysis found that the differences between the groups have decreased over time in five of the seven main constructs that define autism, including emotion recognition, theory of mind, planning and brain size.

In contrast, the group found no such tendency when it comes to the prevalence of schizophrenia, which has remained stable for the past two decades.

Globally, the number of people diagnosed with autism has risen dramatically in recent years, going in the United States from less than 0.5 per cent of the population in 1966 to more than two per cent. In Quebec, the number is approaching two per cent.

The study’s authors say their findings may be due to several factors, including a true increase in the condition, greater public awareness, the fact that a diagnosis leads to greater support, a lowered threshold for diagnosis, the use of “checklist diagnoses” and a greater tendency to diagnose individuals with a normal IQ.

They note that understanding of autism has also evolved “from a narrowly defined clinical picture to a spectrum of conditions of uncertain similarity.” They warn that this blurring of the line could potentially make it more difficult to study the disorder.

Diagnosis criteria have become ‘trivial’

Mottron, for his part, says the research points to a rampant problem of overdiagnosis that he blames on schools, doctors and parents alike. He goes so far as to suggest that a diagnosis can work in a school or parent’s best interest by making them eligible for extra help and funding that they may otherwise not receive.

“Right now, a diagnosis of autism is what allows one to get services in schools,” he said. “When you have an autism diagnosis, you have much greater chances of getting all kinds of extra things compared to another condition, which is total nonsense, because the need for services is independent from a diagnosis.”

He said the criteria for a diagnosis have become “trivial,” including a child’s lack of friends or a dislike of haircuts or tags on clothing.

Mottron acknowledged that the situation is complicated because mild forms of autism do exist. However, he noted that having certain autistic traits isn’t the same as having autism and said it’s “fundamental” for medical professionals to move beyond a simple checklist of symptoms before issuing a diagnosis.

He said the potential for misdiagnosis is problematic in many ways, including the risk of children receiving the wrong treatment.

“The people who are diagnosed as autistic when they aren’t often have problems, but they’re not the same ones,” he said.