Anna Salleh ABC
Autism may be under-diagnosed in girls because they are not as hyperactive as boys, say Australian researchers.
The findings are published in a recent issue of the Journal of Autism and Developmental Disorders.
"We suspect that females are more likely to go undiagnosed with autism because we are just not good at finding them," says Tamara May, who carried out the research as part of her PhD at Monash University in Melbourne, under the supervision of Professor Kim Cornish and Professor Nicole Rinehart from the School of Psychology and Psychiatry.
"Boys often have more problem behaviours like hyperactivity and so they come to clinical attention more often than girls."
Around four boys are diagnosed with autism for every one girl, but May and colleagues were not convinced this is an accurate reflection of autism's prevalence.
"There is no biological cause of autism that's been established to explain that difference between the sexes," says May.
She and colleagues studied 56 children (aged 7-12) diagnosed with autism spectrum disorder (ASD), and 44 typically-developing controls.
The children, half of whom were female, were tested twice, a year apart, for autism and other symptoms. At both points in time, the findings were the same.
"There was no difference in the autism symptoms," says May. "They were quite similar in the boys and girls."
However, the researchers did find the boys had a high level of hyperactivity, which is not a specific autism symptom.
May says symptoms of hyperactivity, like climbing on things and impulsively calling out, are very noticeable to parents and teachers, and could explain why more boys are being diagnosed with autism.
"These are problem behaviours that we pick up and say, 'There's something wrong with this child, let's take them to a psychologist or a doctor to get them assessed'," she says.
"It's like the squeaky wheel gets the oil."
Although both girls and boys with autism in the study had similar levels of communication and social difficulties, May says the boys received more help at school than the girls did.
"We wonder if girls are getting the support they need," she says.
To check if there are many more girls with autism than we think, May says a new Pozible crowdfunding campaign called "Autism Lost Girls" will be launched soon through Deakin University, Geelong, where she is now based.
"If we raise enough money through the community, we will look for mothers and fathers who might have undiagnosed autism," she says. "We want to see how many 'lost girls' we find."