Autism is now so over-diagnosed, following the progressively lowering over 50 years of the diagnostic bar, that by 2029 there will be no objective difference between someone with the condition and the average non-autistic person, an international study warns.
Rates of autism are rising, with between 1% and 2% of western populations diagnosed with the disorder. One in 100 Britons is now considered to be autistic, around a twenty-fold increase from the 1960s, and some scientists are investigating whether the rigours of modern life are to blame.
But, the report says, a study by the University of Montreal and University of Copenhagen, has found that the bar for diagnosing autism has become progressively lower in the past 50 years. If the trend continues, those with the condition will become indistinguishable from people without it by 2029, the researchers estimate.
Professor Laurent Mottron, of the University of Montreal’s department of psychiatry, said: “If this trend holds, the objective difference between people with autism and the general population will disappear in less than 10 years. The definition of autism may get too blurry to be meaningful – trivialising the condition – because we are increasingly applying the diagnosis to people whose differences from the general population are less
The study looked at the diagnostic criteria for 23,000 people with autism from 1966 to 2019.
A diagnosis of autism is based on a series of psychological and neurological tests which look at how well someone can recognise emotions and intentions, their ability to shift from one task to another, activity planning, inhibition, brain volume and their responses to sensory stimulation.
However, the report says the team found that in recent decades the measurable difference between people with and without autism had fallen by as much as 80 per cent. Although the diagnostic criteria remained the same, the way they were interpreted by clinicians has changed, the study discovered.
“Fifty years ago, one sign of autism was a lack of apparent interest in others,” added Mottron. “Nowadays, it’s simply having fewer friends than others. Interest in others can be measured in various ways, such as making eye contact. But shyness, not autism, can prevent some people from looking at others. Autism is a natural category at one end of the socialisation continuum. And we need to focus on this extreme if want to make progress.”
Over-diagnosis also leading to people being included in studies for new drugs and therapies when they do not have the condition, warn the authors. There have been no new drugs for autism in a decade.
According to the report, the researchers believe the over-diagnosis has happened because it is often difficult to access help and support without a clinical diagnosis. Lobbyists have also pushed the message that spotting the condition early is better, leading to a ‘rush to diagnosis’.
Some psychologists are often more comfortable in diagnosis autism rather than an intellectual disability or personality disorder, said Mottron.
Commenting on the research, Carol Povey, director of the National Autistic Society‘s Centre for Autism, said: “This is a detailed and thought provoking study. We should not rush to conclusions about its implications, as there could be many reasons behind the apparent trends identified by the authors.
“Our understanding of autism has changed a lot since it was first identified in the 1940s and there is now widespread acknowledgement that autism is a spectrum. This means that every autistic person is different, but all face difficulties with communication and social interaction.
“Though even better understanding is still needed, professionals are getting better at identifying how autism can manifest differently in people, for instance in women and girls, and how someone’s needs may change over their life.”
To verify that the trend was unique to autism, the research team also analysed data on similar areas from studies on schizophrenia. They found that the prevalence of schizophrenia has stayed the same and the difference between people with schizophrenia and those without it is increasing.
Importance: The definition and nature of autism have been highly debated, as exemplified by several revisions of the DSM (DSM-III, DSM-IIIR, DSM-IV, and DSM-5) criteria. There has recently been a move from a categorical view toward a spectrum-based view. These changes have been accompanied by a steady increase in the prevalence of the condition. Changes in the definition of autism that may increase heterogeneity could affect the results of autism research; specifically, a broadening of the population with autism could result in decreasing effect sizes of group comparison studies.
Objective: To examine the correlation between publication year and effect size of autism-control group comparisons across several domains of published autism neurocognitive research.
Data Sources: This meta-analysis investigated 11 meta-analyses obtained through a systematic search of PubMed for meta-analyses published from January 1, 1966, through January 27, 2019, using the search string autism AND (meta-analysis OR meta-analytic). The last search was conducted on January 27, 2019.
Study Selection: Meta-analyses were included if they tested the significance of group differences between individuals with autism and control individuals on a neurocognitive construct. Meta-analyses were only included if the tested group difference was significant and included data with a span of at least 15 years.
Data Extraction and Synthesis: Data were extracted and analyzed according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guideline using fixed-effects models.
Main Outcomes and Measures: Estimated slope of the correlation between publication year and effect size, controlling for differences in methods, sample size, and study quality.
Results: The 11 meta-analyses included data from a total of 27 723 individuals. Demographic data such as sex and age were not available for the entire data set. Seven different psychological and neurologic constructs were analyzed based on data from these meta-analyses. Downward temporal trends for effect size were found for all constructs (slopes: –0.067 to –0.003), with the trend being significant in 5 of 7 cases: emotion recognition (slope: –0.028 [95% CI, –0.048 to –0.007]), theory of mind (–0.045 [95% CI, –0.066 to –0.024]), planning (–0.067 [95% CI, –0.125 to –0.009]), P3b amplitude (–0.048 [95% CI, –0.093 to –0.004]), and brain size (–0.047 [95% CI, –0.077 to –0.016]). In contrast, 3 analogous constructs in schizophrenia, a condition that is also heterogeneous but with no reported increase in prevalence, did not show a similar trend.
Conclusions and Relevance: The findings suggest that differences between individuals with autism and those without the diagnosis have decreased over time and that 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.
Eya-Mist Rødgaard; Kristian Jensen; Jean-Noël Vergnes: Isabelle Soulières; Laurent Mottron