Autism is the most common condition in a group of developmental disorders known as the autism spectrum disorders. Experts estimate that three to six children out of every 1,000 will have autism. Males are four times more likely to have autism than females. The disease is characterized by impaired social interaction, problems with verbal and nonverbal communication, and unusual, repetitive, or severely limited activities and interests. The cause of this disorder has stumped medical experts. Older parents appear to be more likely to have autistic children. The disorder has been blamed on mercury in vaccines and gluten, a wheat derivative found in many foods, but research has failed to establish a connection between either and autism.