Researchers say changing criteria has resulted in more people being diagnosed with autism. Getty Images

• Researchers say the changing criteria for autism may be resulting in an overdiagnosis of the condition.
• Some experts, however, say that better diagnostic methods are simply recognizing autism in more individuals and at an earlier age.
• Earlier diagnosis allows medical professionals to begin treatments for autism at a younger age.

Autism isn’t what it used to be.

A new study finds that, over time, the differences between individuals diagnosed with autism and those who don’t have autism have decreased.

The researchers say that could mean that more people with less profound symptoms are being diagnosed with the condition.

“The autism category has considerably overextended,” with prevalence rates now 15 times greater than they were a half-century ago, said Laurent Mottron, MD, PhD, DEA, a study author and professor in the department of psychiatry at the University of Montreal, and the chair on cognitive neuroscience in autism.

“Most neurogenetic and child psychiatry disorders that have only a loose resemblance with autism can now be labeled autistic,” he said.

For instance, Mottron said, “you could not [have] ADHD and [autism] before 2013. Now you can.”

He added, while “this is justified in some cases that have both presentations,” it also gives doctors the ability to label someone as having autism who just has “pure” ADHD with “a heavy impact on socialization.”

The findings from the study published in the journal JAMA PsychiatryTrusted Source could indicate that autism is being overdiagnosed. 

Or, it could mean that early detection has led to more awareness of the many manifestations of autism, with symptoms ranging from mild to profound.

Either way, “Possible changes in the definition of autism from a narrowly defined and homogenous population toward an inclusive and heterogeneous population may reduce our capacity to build mechanistic models of the condition,” the study concludes. 

In other words, the broader definition may make it more challenging to model how the autistic brain works, said Mottron.

He contends that the implications of a broader definition may include loss of specialized knowledge and clinical experience around other conditions now considered forms of autism.

It could also increase strain on available autism services.

Better diagnosis or overdiagnosis?

Other experts don’t dispute that medical professionals are casting a wider net in diagnosing autism.

But they put a more benign spin on the implications.

“As a clinical psychologist I am less concerned with the narrowing gap and attribute that more to research and awareness associated with the disorder,” Ashley Baker, PsyD, owner of Pavilion Psychological Services in Cummings, Georgia, told Healthline.

“[Healthcare workers] have worked tirelessly to educate communities and parents about early warning signs,” she added. “This leads to early intervention and diagnosis.”

Thomas Frazier, PhD, the chief science officer at Autism Speaks, told Healthline: “Autism is not being overdiagnosed.”

“The core features of autism — social communication and inflexible, repetitive behavior — have remained the same since the beginning,” said Frazier.

He noted that any time a condition has milder cases identified it can cause the difference in the factors that cause the ailment to get smaller.

“It does not mean that the condition is overdiagnosed,” Frazier said. “It just means we are recognizing milder manifestations that still are associated with significant functional challenges.”

Frazier said that recent changes in the diagnostic criteria for autism have been a factor in increasing autism diagnoses.

However, he added, “Rather than diluting the definition of autism, it appropriately reclassified three distinct conditions that share a unique mix of primary symptoms, allowing us to better understand the underlying processes that are involved in these areas.”

“What is most important to understand is that, with more people getting an appropriate diagnosis earlier in life, more people with autism are getting the care and support they need to be successful,” said Frazier.

Criteria changes

The studies examined in the meta-anaylsis led by Mottron were published between 1966 and 2019.

During that period, autism prevalence has increased from under 0.05 percent at age 8 in the United States to 1.47 percent, with a lifetime prevalence rate now estimated at more than 2 percent.

Autism was initially identified as a childhood disorder in the 1940s. The diagnostic criteria for autism have been changed several times over the decades. 

In 2013, the latest revision, Trusted Source of the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders (DSM-5) expanded the definition of autism.

It combined the previously separate diagnoses of autistic disorder, Asperger syndrome, childhood disintegrative disorder, and pervasive developmental disorder-not otherwise specified (PDD-NOS) under the now familiar umbrella of “autism spectrum disorder.”

“People who are diagnosed with autism spectrum disorder still have symptoms and challenges associated with classic autism,” Rebecca Sachs, PhD, a licensed psychologist who specializes in counseling patients with autism, obsessive-compulsive disorder, and anxiety disorders, told Healthline. 

Sachs compares the growing diversity of autism diagnoses to those of ADHD, another disorder whose diagnostic criteria have evolved as knowledge and the research base of the condition has expanded.

Yagnesh Vadgama, vice president of Clinical Care Services — Autism at Magellan Health, told Healthline that it’s important to try to understand why autism diagnoses have increased over time while also recognizing that the condition tends to be under-diagnosed in some populations, such as females, minority groups, and lower-income families.

On the one hand, he said, “we’re not seeing enough of the full evaluation” of autism as defined in the DSM-5. 

On the other, “Certain populations may be overdiagnosed,” said Vadgama, pointing to a 2016 University of Washington study published in the journal Autism, where a reanalysis of previously diagnosed autism patients determined that about 9 percent shouldn’t have been classified as autistic. 

“We need reevaluations in a given time frame,” he said. “Patients should be reevaluated more frequently than they are now.”