It is a question that has long stumped researchers. But now light has been shed on why boys are more at risk of autism. University of Iowa scientists believe they have collected the first ever evidence of a'protective effect' in females. Trials on mice showed males who had a known genetic cause of autism showed signs of being on the spectrum. This genetic deletion, or a missing stretch of DNA, plays a role in one in every 200 cases of autism spectrum disorder (ASD), experts claim. Figures suggest four boys are diagnosed with autism - which often causes sufferers to struggle with social interaction - to every one girl.