Annette Lewns has more experience than most of the different ways in which boys and girls with autism are treated. Her 14-year-old son, Ryan, was diagnosed when he was three and a half. But doctors refused to diagnose her 12-year-old daughter, Rachel, until she was nine.

"What angers me is that for years I was dismissed by doctors purely because Rachel was a girl. Ryan was spotted very quickly because the autism symptoms that doctors look for are so male-orientated," said Lewns. "But Rachel's autism was hidden unless you knew where to look for it.

"Rachel could express herself, she had a couple of friends and understood emotions if someone was at an extreme: really upset or really happy. But you didn't really have to look too hard to see she didn't genuinely understand emotions or relationships: she was just mimicking scripts and scenarios from TV."

"The doctors failed time and time again to see through her coping strategies. I fought for years but I was confronted with a wall of disbelief and scepticism. They were simply unable to understand that a girl might present differently to a boy."

While Ryan's condition was acknowledged by their local authority, and he is now at a specialist school, Rachel continues to struggle at a mainstream school. "Ryan is being taught all sorts of tools and techniques to cope with his condition but Rachel is not," said Lewns.

Estimates of the ratio of females to males diagnosed with Asperger's syndrome or high-functioning autism varies from 1:4 to 1:10. No one understands this gender disparity: whether women really are less likely to be on the spectrum than men – or whether doctors are failing to spot the disorder in women.

Opinions are divided: Richard Mills, director of research at the National Autistic Society (NAS) says he "would not be surprised" if the true ratio was twice as high, with one woman on the spectrum for every two men. Dr Judith Gould, director of the NAS's Lorna Wing Centre, thinks the ratio could be even narrower, with 1:1.5 female:male.

We may soon have an answer. Mills is leading the UK arm of a two-year international programme, Autism in Pink, which will look at the condition in women, focusing on the stress, social exclusion, vulnerability and misdiagnosis they suffer.

It follows concerns about reluctance to diagnose women. One recent survey by NAS found girls may wait longer than boys for a diagnosis and are more likely to be misdiagnosed: just one-fifth of girls with Asperger's syndrome who responded to the survey were diagnosed by the age of 11, compared with half of boys.

The UK is leading the research side of the programme. Last week, Mills signed up the first two of the 12 women with Asperger's he needs to work with researchers over a two-year period.

"I hope the programme will be the first step to ending the current trend for gender to be a barrier to diagnosis and post-diagnostic support," he said. "Because research in the past has largely concentrated on males, the way we understand autism tends to be very much based on the experiences of men and boys with the condition. People are reluctant, for some reason, to make a diagnosis in girls and women."

This reluctance is exacerbated by the fact that girls and women with Asperger's or high-functioning autism can be more adaptive than boys: they are commonly better at hiding things or seeming more sociable, masking what doctors traditionally think of as the signs of autism.

But the strain of trying to appear "normal" can be immensely stressful. Gould said it results in "many of the girls we see having developed secondary problems such as anxiety, eating disorders or depression".

This can also mean that misdiagnosis of girls and women is also a problem. The survey found 42% of females had been wrongly told they suffered psychiatric, personality or eating disorders, compared with 30% of males.

There is also the problem that the gender difference becomes a self-fulfilling prophecy: because more males are diagnosed than females, it is their symptoms and behaviours that experts have studied. The so-called screening tools, developed to help diagnosticians spot the syndrome, focus on culturally "male" interests, such as computers, trains and cars, rather than things more likely to appeal to a girl, such as animals, soap operas or fashion. Gould is rewriting the NAS's diagnostic interview for social and communication disorders to include "gender-neutral" cues.

Even when an accurate assessment is given, however, it is no guarantee that the necessary support and help will materialise: the NAS survey found women continue to struggle after diagnosis, with half of females with Asperger's or high-functioning autism – compared with 39% of males – saying it made no difference to the support they received.

Lucy Clapham, 25, spent years being turned away by doctors who insisted "girls don't get autism" and told her to simply "act normal and read female magazines". "I am certain that my diagnosis was delayed because of the fact that I am a girl," she said. "My mum first noticed something when I was about six but our GP laughed at the suggestion. I've gone to counsellors, doctors and psychiatrists but all of them, including my teachers, refused to see I had classic autism even though I had casebook symptoms: almost no speech until I was five, no friends, hours spent staring at the washing machine, lining toys up and flicking my fingers in front of my eyes."

When she was 12, Clapham became violent, aggressive and developed multiple tics, obsessions and compulsions. "I stopped talking outside of the house and sunk into an inner world," she said.

After two more years and about eight counsellors, Clapham's GP referred her to a child psychiatrist. "She was adamant that girls didn't get autism, they just had 'traits'," said Clapham. "She claimed that I just needed to 'act normal' and that by buying nice clothes and reading women's magazines I could learn to be 'normal'. The only diagnosis I received from her was depression and anxiety."

After leaving the children's mental health service "none the wiser and possibly with more mental health problems than when I had arrived", Clapham was sent to the adult mental health service and, after a long battle, to the Maudsley hospital in London, where she was finally diagnosed with autism, Tourette syndrome and obsessive-compulsive disorder.

"I was still refused services, however, partly because there were none available and partly because our local authority was not willing to fund an out-of-town, specialist autism service," said Clapham. "I ended up getting sent to a college for the blind where I developed more mental health problems and became very aggressive because no one understood me or my autistic behaviour.

"When I was 20, I ended up in care because my mother couldn't cope with my aggression and anxiety."

Clapham stayed there for three years but still struggles. "Despite my diagnoses, some people still seem to believe that autism is a 'boy thing'," she said.

There is no clear understanding about how many girls and women are being missed – or wrongly diagnosed – and for how long. But that may soon change: the first neuroimaging analysis of women and men, with and without ASD, has been under way for the past two and a half years at King's College's Institute of Psychiatry (IoP) and the Autism Research Centre at the University of Cambridge. It's hoped this research could provide the clues. The final stage of the project is about to begin, with results expected in months.

"It's very exciting," said Dr Michael Craig, a senior lecturer and honorary consultant at the IoP's department of forensic and neurodevelopmental sciences. "We could well be looking at gender-specific treatments for Asperger's being developed in quite a short period of time."

What is autism?



First identified in the 1940s, autism is a developmental disability that lasts a lifetime and affects someone's interaction with other people – how they communicate with and relate to them. It is a spectrum condition, affecting some more seriously than others. While some lead fairly independent lives, others suffer serious learning disabilities and need extensive support. Many who have an autism spectrum disorder can be badly affected because they have trouble processing sounds, sights and smells.

Around half a million people in the UK have autism, according to the National Autistic Society (NAS). What causes it is still unclear. "There is strong evidence to suggest that autism can be caused by a variety of physical factors, all of which affect brain development. It is not due to emotional deprivation or the way a person has been brought up," the NAS says. Genetic factors are assumed to be responsible, and scientists are trying to pin down which genes are involved. Genetic testing to enable earlier diagnosis is therefore still a long way off.

Many people are not diagnosed until they reach adulthood. A recent NAS study of more than 8,000 people with autism, parents and carers found 52% were initially misdiagnosed. One in three adults with the condition say they have developed serious mental health problems because they have not received enough support to help them cope with the difficulties autism brings.