With more ... attention, the lost girls on the autism spectrum will not be lost for long.

Doctors often focus on boys, write Craig and Marc Kielburger.

When it comes to autism, early intervention is best.

At the Center for Autism and the Developing Brain in White Plains, N.Y., children under the age of three work on language and communication skills, and increase co-operative play.

“We get the families started as early as possible,” says founding director Dr. Catherine Lord. There’s one hitch in this plan, she adds: “It’s a rare day when there’s a girl.”

For decades, medical consensus presumed autism as a predominantly male condition, a result of an “extreme male brain.” Studies were cited that it affects boys at a rate four times higher than girls. That thinking is starting to change.

New research has uncovered a blind spot for women and girls on the spectrum, a gender bias that leaves them undiagnosed.

A complex neurobiological condition, autism is a spectrum of characteristics that are different in every individual. To complicate matters, there are no brain scans or blood tests to diagnose autism.

In the absence of physical tests, doctors rely on behavioural assessments that come with their own biases. Right from the outset, doctors focused on boys because they tended to exhibit the most obvious signs of atypical behaviour, says Gina Rippon, a leading neuroscientist and professor of cognitive neuroimaging at the Aston Brain Centre in the U.K.

This included a disinterest in socializing.

Young boys are stereotypically rowdy and sociable. So when boys obsess with maps or avoid group play in favour of time alone, society recognizes that behaviour as neurologically atypical, a symptom of their need to categorize and find routine. When girls fixate on dolls or books, when they’re obsessively neat or shy and quiet, that’s seen as normal — deferential female behaviour.

Early focus on so-called boys’ behaviours set the parameters for what doctors came to think of as autism. While girls and boys on the extreme end of the spectrum share behavioural patterns and are diagnosed in roughly equal numbers, girls on the less extreme end, whose autism manifests differently than boys, have slipped under the radar.

“It’s become a self-fulfilling prophecy,” says Rippon.

It’s not uncommon for parents to be told their daughters can’t be on the spectrum, according to Beth Finkelstein, executive director of Felicity House, an autism support group for women. Girls are often misdiagnosed with attention deficit hyperactive disorder (ADHD) or obsessive compulsive disorder (OCD); doctors who still think of autism as a disproportionally male condition often look for other explanations. As a result, girls may miss out on early interventions.

A correct diagnosis brings with it an ecosystem of support, from educational accommodations to social services. For many, there is also a sense of community. Rippon, Finkelstein and Lord have each met women diagnosed later in life who found relief in the knowledge. “Knowing that other people experience the world in a similar way is incredibly helpful,” says Lord.

As new research — and vocal parents — expand how we think about autism in girls, doctors are creating new services to meet their needs, from amending diagnostic tools to new guidebooks that help navigate puberty and social relationships. With more understanding and attention, the lost girls on the autism spectrum will not be lost for long.