According to the Autism speaks: "Autism, or autism spectrum disorder (ASD), refers to a broad range of conditions characterized by challenges with social skills, repetitive behaviors, speech and nonverbal communication". As this is a spectrum, this can include conditions that have been previously categorized separately, notably: autism, Apserger's syndrome and childhood disintegrative disorder.
Children who are affected by ASD have trouble communicating and interacting with others. They may not respond to their names or even look at other people. In severe cases, they may become aggressive or injure themselves. Adults who are affected by ASD can have difficulty functioning socially, but are more likely to be viewed as subclinically autistic. ASD cannot be cured, but there are many resources dedicated to helping those who are affected live a more "normal" life.
Infantile autism is characterized by extreme self-isolation, difficulty forming emotional attachments and communicating. It also, more generally speaking, describes any non-communicating behaviour in children. Autistic children find it very difficult to use or comprehend language or any kind of communication. The autistic child always takes longer to acquire language, and some never develop any language skills at all. About half are not speaking any words by the age of five. When language does come it is usually halting and stilted. The child often uses words in unusual ways or even makes up his own words.
The apparent withdrawal of the autistic child has traditionally been seen as resulting from an unresolved conflict between fear and curiosity in social encounters. Recent evidence, however, leads researchers to believe there are genetic preconditions, such as a "fragile X" chromosome, that increase the likelihood of the condition. Rather than a single flawed gene causing a disease autism appears to be brought on by unknown environmental influences coupled with a dimly understood combination of genes that makes people vulnerable. According to another hypothesis, autism stems from immature development of some parts of the brain in combination with hyperdevelopment of other parts, and possibly abnormal brain chemistry.
Evidence for a genetic root for autism is that the rate of autism in the general population is about two-tenths of a percent or less, but for siblings of an autism patient it jumps to around 3 percent. And for an identical twin of an autism patient, someone who shares all the patient's genes, the rate is 60 percent or more. In 1997, an American study linked subliminal autism in parents to full-blown autism in their 380 children.
Autism usually appears by age 3, mostly in boys. Studies in the USA and in the UK have established an incidence of about one autistic (psychotic) child per 2,500 births. Since true autism in this sense seems to represent about ten percent of children loosely called autistic, then around one child in 25,000 could be a realistic estimate of classical autism (including mild or subliminal or sub-clinical autism).
Autism rates reported to authorities in California nearly quadrupled between 1980 and 1994, to 208 cases per 100,000 children.
A 1997 study estimated that 80% of the 400,000 autistic people in the USA were also mentally retarded, while a few had IQ's in the genius range.