School leaders, health experts and parents have called for action to address the underdiagnosis of girls with autism.

The Big Shout conference, organised by the NAHT heads union in London, will today draw attention to the “misinformation, underdiagnosis and lack of representation for girls on the autistic spectrum”.

Professor Francesca Happé from King’s College London, who will be speaking at the event, said there were many more girls on the spectrum than had previously been thought.

“Until recently, it was thought that boys outnumbered girls on the spectrum by five or even 10 to one,” she said.

“However, recent epidemiological studies suggest we are missing autism in females, and there are in fact only two or three times as many boys as girls affected.”

This means there are potentially “thousands” of girls on the spectrum who have not been diagnosed, or who might have been misdiagnosed, she said.

“Much of the research into autism has been focused on boys, and has often explicitly excluded women and girls because of the assumption that they are very rare,” Professor Happé added. “This is a huge problem; our diagnostic criteria and processes are based on boys and may not serve girls well.

“For example, clinicians look for unusual special interests, like a fascination with electricity pylons, and may miss a girl with a very narrow and obsessive interest in (facts about) horses or a boy band, because those look on the surface like ordinary hobbies.”

“Pressure to conform socially” led some young women to “camouflage their autism” by deliberately copying popular peers.

However, this “flying under the radar” could damage girls’ mental health because it was  “exhausting and anxiety-provoking”.

The academic also noted that girls on the autism spectrum could get into trouble with teachers because they did not read social cues well, and might not receive the right interventions. 

Professor Barry Carpenter, chair of the Autism and Girls Forum, said the Big Shout conference aimed to “share evidence and experience, thoughts and ideas, to develop a call for action that can be presented to politicians, professionals, families and the public”.

NAHT general secretary Russell Hobby said girls on the autistic spectrum had “suffered too long from a lack of investment and research into their condition”.