According to the Mayo Clinic:
“Autism is one of a group of serious developmental problems called autism spectrum disorders that appear in early childhood — usually before age 3. Though symptoms and severity vary, all autism spectrum disorders affect a child’s ability to communicate and interact with others.
The number of children diagnosed with autism appears to be rising. It’s not clear whether this is due to better detection and reporting of autism, or a real increase in the number of cases or both.
Children with autism generally have problems in three crucial areas of development — social interaction, language, and behavior. But because autism symptoms and severity vary greatly, two children with the same diagnosis may act quite differently and have strikingly different skills. In most cases, though, children with severe autism have marked impairments or a complete inability to communicate or interact with other people.
Some children show signs of autism in early infancy. Other children may develop normally for the first few months or years of life, but then suddenly become withdrawn or aggressive or lose language skills they’ve already acquired.
While there is no cure for autism, intensive, early treatment can make a big difference in the lives of many children with the disorder.”