Autism experts are calling for changes in diagnostic testing, saying the current approach is failing to identify the true number of females with the disorder.
They say a massive imbalance in the number of autism diagnoses between the sexes could be attributed to more subtle symptoms in females that are either dismissed by clinicians, or undetected by current testing, which focuses on signs associated with male behaviour.
American psychologist Dr Lori Ernsperger, who specialises in working with girls with autism, believes the high ratio of boys to girls diagnosed with the condition suggests a flaw in current diagnostic questionnaires.
"In some children and individuals that are severely impacted with autism, the ratio of males to females is about four to one," she said.
"When we move on that spectrum to individuals that are mildly affected by the disorder - often referred to as Asperger's syndrome or high functioning autism - the ratio of boys to girls gets to 10 to one."
Claims clinicians overlook subtle signs in girls
By all appearances Sienna Quarmby is a normal and talented 10-year-old, but when she was small her mother noticed Sienna would have extreme reactions to small things.
"We all kind of ... just assumed she was quirky," Danielle Quarmby said.
"When she was in prep ... the prep teacher said that after observing Sienna for the first term ... she thought that it would benefit Sienna to be assessed."
Sienna was eventually diagnosed as having Asperger's syndrome. Her two younger brothers also have different forms of autism.
Psychologist Danuta Bulhak-Paterson says in initial testing, health professionals are often looking for more obvious signs a child is on the autism spectrum.
"I think they're looking for more severe characteristics in the clinical interview. They're seeing the girl as being polite, smiling, giving eye contact and they just dismiss it," she said.
Ms Bulhak-Paterson says she is the only clinical psychologist in Australia who specialises only in autism in women. Sienna Quarmby is one of her clients.
Ms Bulhak-Paterson believes there is orthodoxy within the health profession that still refuses to acknowledge that autism presents differently in women to men.
"There are many health professionals who don't believe the female presentation," she said.
"They make comments like 'Oh it's just over diagnosed, there's nothing clinical' and that is very frustrating for me and for parents because they live it and they know how real it is and how distressing it is for their families."
Calls for testing questionnaires to be adapted
The challenge in diagnosing girls with autism is a focus of Dr Ernsperger, who is speaking at a conference in Melbourne.
She believes the diagnostic questionnaires doctors use for autism focus mainly on the male characteristics of the disorder and are yet to be adapted for girls.
"That doctor is going to do a diagnostic checklist ... it may have 20 questions or so [but] they're the sort of questions that lend themselves to male behaviour or boy behaviour," she said.
Dr Ernsperger says she has been contacted by many women with autism spectrum disorders who say they have been able to mask their symptoms and be successful in school and university while struggling in other areas of life such as forming enduring friendships.
Getting a diagnosis is one of the most important and empowering things that I've ever done. It's given me a language to understand myself.Tori Haar
"I get a lot of emails from girls and women on the spectrum who say they're good in school, meaning they could mask their behaviours in school," she said.
"And you hear that ... quite often from women on the spectrum."
There needs to be a change in the way autism disorders are diagnosed, according to Dr Ernsperger.
"Instead of rewriting these testing tools for autism, we should have different scoring levels. A boy would have to score 18/20 where the girl would have to score 16/20 in order to move on to the secondary testing for further diagnosis," she said.
When Tori Haar was a teenager, her brother was diagnosed with autism. She knew there was also something different about herself but finding out what was discouraged.
"I got referred to this psychologist who basically told me that I was wanting to have this developmental disability that couldn't be cured, that couldn't be treated," she said.
The psychologist she saw went even further, telling her "that I was somehow messed up in the head because it was something that I wanted for personal reasons, rather than trying to find out reasons for how I think and how I am".
When she was eventually diagnosed with Asperger's syndrome, Ms Haar says it gave her the means to cope. She is now a psychologist.
"Getting a diagnosis is one of the most important and empowering things that I've ever done," she said.
"I feel like it's given me a language to understand myself and express how I'm feeling and to describe my experiences to others."