When autism pioneer Uta Frith started her career as a neuroscientist back in the late Sixties, hardly anyone outside a small academic cohort had heard of autism, a lifelong condition which affects how people communicate and interact with the world. “It was considered an uncommon disabling condition that affected a tiny proportion of children, around four in 10,000,” says Prof Frith, now based at the Institute of Cognitive Neuroscience at University College London. “When I did my PhD thesis on autism, people asked me, why would you study something so rare?”

Today, autistic spectrum disorder is widely known and even celebrated as a facet of neurodiversity – partly thanks to Prof Frith’s efforts to raise its profile and highlight the problem of widespread underdiagnosis.

Around one in 100 people in the UK are living with autism, according to the National Autistic Society. It’s now understood that it can cause mild symptoms or in more severe cases include difficulties with social interaction, communication as well as unusual sensory perception and unusual patterns of thought and physical behaviour.  

The numbers affected continue to rise: a study published last month by the University of Exeter found that diagnoses have shot up by 787 per cent between 1998 and 2018. But though many welcome signs of improving awareness of autism, some experts – including Prof Frith – believe we may now be overdiagnosing it.

“I never thought I would say this since I was eager to embrace a widening of the diagnostic criteria, but I had no idea just how elastic it would become,” says Prof Frith.

“The Exeter data strongly suggests that the diagnosis of autism has been stretched to breaking point and has outgrown its purpose. If the purpose is to predict what an individual’s needs are, this is no longer possible.”

Experts agree that the rise in diagnoses of autism probably don’t reflect a real rise in incidence, and is instead down to increased identification.

Tim Nicholls, head of policy and public affairs at the National Autistic Society, says greater awareness about autism is causing more people to come forward, pointing out that the Autism Act of 2009 made it mandatory to have diagnostic services for adults. “In the past, unless your autism was picked up as a child, you may not have been identified at all. Now more adults are seeking diagnosis for themselves.”  

The trend is being driven too by a broadening definition of what constitutes autism, and a better understanding of how it can present in women and girls – though boys are still three times more likely to be diagnosed.

Ashleigh Tompkins, 26, lives in Bournemouth and was diagnosed with autism when she was 15. She says: “Women and girls are underestimated in the field of mental health, partly because we have a talent for masking, hiding away anything that may appear to be a problem. We are trained from early childhood to appear as quiet and unobtrusive. Women are under-reported because we are simply not taken seriously.”

She says she always knew she was different from other students at her school and was labelled a problem child, even though she was badly bullied. “I think they thought I was smart but couldn’t focus, was aggressive and angry and probably a whole host of other things.” She was diagnosed quite late in her mid teens but only began to accept her diagnosis of ASD when she went on to higher education and began to research her condition.

Although she is grateful that the condition is now being recognised more widely, she is concerned that people may now assume a diagnosis of autism too readily because it is so well known. “While I do think that the number of people getting diagnosed is playing catch-up, I also feel that people will take the first excuse to explain something that they don’t understand. Parents of very young children will latch on to autism because it is the first buzzword that they think of. There is a worry that their confirmation bias will twist any of their children’s behaviours into fitting that narrative.”

A misdiagnosis can prevent doctors from identifying other serious ailments with similar symptoms. Johanne Hewlett says her son William was misdiagnosed with autism at the age of seven when he was still at primary school. 

In fact, she now thinks he was suffering from PANS/PANDAS, an autoimmune condition where a common infection is thought to trigger behavioural problems. The condition has only recently been described and remains a controversial area.