Suzanne Amara's daughter, Janey, was 3 years old when she was diagnosed with autism.
These days, no one would mistake that her daughter has the neuro-developmental disorder, Amara said. Janey, who is now 9, is nonverbal and has what is considered severe autism. But there were signs early on that Amara believes she may have overlooked simply because of her daughter's sex.
"There might've been things she was demonstrating that I didn't see because she was a girl," said the mother of three, who writes the blog Rarer In Girls ... My Daughter With Autism.
"Maybe, I sort of comforted myself with thinking, 'Well, she's not autistic, because she's a girl,'" Amara said.
According to the Centers for Disease Control and Prevention, autism spectrum disorders, or ASDs, are five times more common among boys than girls. One in 54 boys in the U.S. has been diagnosed with autism, compared to just 1 in 252 girls. But a growing body of research hints that the significant sex-based differences in autism diagnoses are a result not just of biological differences, but of a failure to recognize ASD in girls.
One study, published in the November edition of the Journal of the American Academy of Child and Adolescent Psychiatry, analyzed data from more than 3,600 children, many of whom were considered to exhibit autism-like traits, according to a checklist scoring various social behaviors.
The children were then given two tests. In one, they were shown photos of other children and asked to identify whether those kids were happy, sad, angry or fearful. In a second, they were shown an animated triangle and circle that moved across a screen and asked to describe what the movement revealed about the shapes' "emotions." A triangle moving in a purposeful manner, for example, was meant to evoke a happy feeling.
Both girls and boys with autism-like traits struggled to identify the correct emotions in the triangle task, and boys with autism-like traits also struggled with the facial recognition task.
However, girls with autism-like traits were able to recognize emotions from photos just as well as girls without autism did. Because many experts believe failure to recognize facial expressions is one of the more direct signs of autism, the researchers argue that doctors may need to use more subtle assessments to accurately diagnose the disorder in girls.
"If girls with ASD are developing strategies to compensate for ASD like traits (such as [difficulty with] emotion recognition), then it is possible that they are less likely to be diagnosed," study researcher Radha Kothari, a research associate with University College London's Institute of Child Health, wrote in an email to HuffPost.
"Much of the research conducted on autism, which goes on to define our idea of the disorder, is conducted on males rather than females," Kothari wrote, adding, "This creates a cyclical system, in which our understanding of ASD is mainly based upon presentation of it in males, which means that more males are likely to be diagnosed."
"It's likely that we are missing girls who are high-functioning and don't have additional co-morbid problems," echoed Francesca Happe, a professor of cognitive neuroscience at King's College London and president of the International Society for Autism Research.
Happe cautioned against overstating the new study's potential implications but called it interesting. In February 2012, she was an author on another autism investigation, which found that girls who had similarly high levels of autism-like traits as their male counterparts, but who did not have additional intellectual or behavior problems, were less likely to meet diagnostic criteria. Those results suggested the girls might be "fly[ing] under the radar," Happe said.
With so much about autism still a mystery and so many questions about its causes unanswered, experts warn that it is difficult to tell whether sex-based differences in autism rates are a reflection of biology, under-diagnosis or both. Evidence does suggest there is a "female protective effect." In other words, it may take more genetic or environmental risk factors to "tip [girls'] brain development into the realm of autism," as the nonprofit Autism Speak's website puts it.
Whatever the reasons, parents of girls with autism, like Amara, say the experience can be a lonely one. "I've thought, 'Are there no other girls like Janey?'" she said. Amara has connected with families in similar situations online, but day-to-day she and Janey have never encountered another girl with similarly severe autism.
"It's pretty isolating," Amara said. "It's almost all parents of boys."