Girls are frequently diagnosed with autism at older ages than boys and new research suggests that may be because they present with different symptoms.

Overall, girls displayed greater difficulty with social cues while boys presented with more noticeable differences including repetitive behaviors like hand-flapping and highly-restricted interests, researchers say.

The findings come from an analysis of data on children with autism participating in the Interactive Autism Network, an online registry with information on nearly 50,000 people with the developmental disorder and their families that’s housed at the Kennedy Krieger Institute.

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“This and other studies suggest that girls with ASD, as well as perhaps older women with this disorder, differ from males in key symptoms and behaviors, particularly around social interactions,” said Paul Lipkin, director of the Interactive Autism Network who led the study, which was set to be presented this week at the Pediatric Academic Societies annual meeting in San Diego.

“We must determine if the less recognizable symptoms in girls are leading not only to delayed diagnosis, but also under-identification of the condition,” Lipkin said.

On average, girls were diagnosed with Asperger’s syndrome a half-year later than boys, the study found. Significant differences in the age at diagnosis were also seen among those with pervasive developmental disorder.

The most recent federal figures indicate that boys are nearly five times more likely than girls to be diagnosed with autism.

However, the new study suggests this disparity may be evolving. When Lipkin and his colleagues compared information collected between 2006 and 2009 to 2010 and 2013, they found that the proportion of girls diagnosed with autism increased, potentially due to greater public awareness, they said.