Although statistics from the Centers for Disease Control and Prevention published last year show a 78% increase in the prevalence of autism spectrum disorders (ASD), a study has found that new diagnoses of ASD have stabilized in the United Kingdom. The researchers used anonymized data from UK health records databases to investigate whether British children were being diagnosed at rates comparable to American children. They found that while there was a spike in diagnoses during the 1990s, ASD diagnoses have since plateaued.

The researchers extracted data from the General Practice Research Database (GRPD), a database with about three million records from over 300 representative general practices—accounting for around five percent of the population—in the United Kingdom. They focused on cases of children diagnosed with ASD who were born after 1996, calculating the annual prevalence (number of people living with ASD) and annual incidence (number of new diagnoses).

According to the results, the annual prevalence of ASD was approximately 3.8 per 1000 boys and 0.8 per 100 girls. The annual incidence was approximately 1.2 per 1000 boys and 0.2 per 1000 girls. Girls were 75% less likely to be diagnosed with an autism spectrum disorder than boys.

These rates indicate a prevalence of nearly 4/1000 children in the UK, which is much lower than the United States’ 11/1000. Notably, this discrepancy closely resembles the difference in diagnosis rates of ADHD between the two countries. This may suggest a fundamental difference in the approach to diagnosing psychiatric and neurological disorders on either side of the Atlantic.

While it is tempting to connect the rise in prevalence to better understanding of autism spectrum disorders to the higher rate of diagnosis, the researchers note that there were similar increases in other parts of Europe and North America during the same period. The researchers state that the “actual cause of the dramatic rise in the 1990s remains a mystery,” but they do remind readers that any link between ASD and the MMR vaccine has been discredited.

This research is published in the journal BMJ Open. Learn more about how iLs works with autism on our autism page.

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