Commonly it is known that autism spectrum disorder is much more common in boys than girls. Understanding this, researchers from Kennedy Krieger Institute in Baltimore decided to explore possible gender differences that might impact this neurodevelopmental disorder. The symptoms of autism appear much less severe in girls, the new study finds, and this may result in delayed diagnosis for many children.

To gather detailed statistical information about kids with this disorder, the researchers went directly to the source: the Interactive Autism Network, a web-based family registry. All told, the system contained data for 15,644 children under the age of 18 collected between November 2006 and January 2013. For 9,932 of these children, the network made available their age at first diagnosis, while for 5,103 of these children, the network contained a complete, scored Social Responsiveness Scale. This test identifies the presence and severity of social impairment.

And so the researchers generated and analyzed the necessary data to make comparisons. The gender differences, they discovered, were distinct.

Symptomology

First, the researchers calculated the male to female ratio at precisely 4.54 to 1. Since the ratio was believed to be about 4 to 1, this imbalance between boys and girls is greater than expected.

In terms of symptoms, the researchers found striking sex differences. Girls struggled more with the subtleties of social cognition — the ability to interpret social cues — while boys more often displayed severe mannerisms (repetitive behaviors like hand flapping, for instance) and much more restricted interests. Additionally, older boys (those between the ages of 10 and 15) were far more likely to find social awareness and communication difficult.

The researchers also found the girls were diagnosed with pervasive developmental disorder at a mean age of 4 compared to 3.8 for boys, while a diagnosis of Asperger's syndrome was delivered at a mean age of 7.6 for girls compared to 7.1 for boys. Two separate classifications of autism spectrum disorder, pervasive developmental disorder impairs basic skill development, while Asperger’s affects language and behavior.

One additional fact is of note: Between 2010 and 2013, the proportion of girls diagnosed with autism increased in comparison to the years 2006 through 2009. This increase may be due to growing public awareness, propose the researchers, who presented their results at a Pediatric Academic Societies meeting.

“We must determine if the less recognizable symptoms in girls are leading not only to delayed diagnosis, but also under-identification of the condition,” Dr. Paul Lipkin, director of the Interactive Autism Network at Kennedy Krieger, stated in a press release. If this is the case, many adult women may be unaware of their condition, and, quite possibly, still hoping for some long-overdue intervention.

Source: Chen B, Marvin AR, Lipkin PH. Gender Differences in Diagnosis and Social Characteristics of Children With Autism (ASD) from a U.S. Registry. Pediatric Academic Societies annual meeting. 2015.