Researchers and therapists have developed several sets of diagnostic criteria for autism. The term Asperger syndrome is sometimes used to describe people with autistic behavior but well-developed language skills. Girls with Rett's syndrome, a sex-linked genetic disorder characterized by inadequate brain growth, seizures, and other neurological problems, also may show autistic behavior. PDD - NOS, Asperger syndrome, CDD, and Rett's syndrome are sometimes referred to as autism spectrum disorders. Since hearing problems can be confused with autism, children with delayed speech development should always have their hearing checked.
Children sometimes have impaired hearing in addition to autism.
However, estimating IQ in young children with autism is often difficult because problems with language and behavior can interfere with testing. A small percentage of people with autism are savants. These people have limited but extraordinary skills in areas like music, mathematics, drawing, or visualization. Autism has no single cause. Researchers believe several genes, as well as environmental factors such as viruses or chemicals, contribute to the disorder.