Something seems to protect girls from developing ASD and other developmental disorders. That "something" could be hormone levels in utero, epigenetic factors that turn autism susceptibility genes "on" and "off" during development, or the fact that young girls have in general better social skills than boys and so need a bigger "dose" of what causes ASD to cross that threshold to being impaired. It is also possible that a proportion of girls with mild autistic traits lose those traits early on and so escape detection by 8 years of age (the age of the children in the CDC study).
Often, the symptoms of ASD appear as extreme shyness or anxiety in girls, masking that they may not be responsive to the social cues of others. And while fixated interests are common in both sexes on the autism spectrum, girls tend to focus on topics such as on ponies, princesses, dolls or drawings -- common passions for non-autistic girls, too. Boys, on the other hand, may become stuck on less typical activities, such as lining up blocks or running sand through their fingers. As a result, doctors may miss that some of their female patients show signs of autism.
Better understanding of the gender differences in ASD will lead to more effective early interventions for girls, Szatmari says.
Image: Shy girl, via Shutterstock.