Autism is a disorder that makes itself known as early as three years old or lesser. It is considered a part of the set of Pervasive Developmental Disorders (PPDs), or, as preferred by some schools of thought, Autism Spectrum Disorders (ASDs). The main characteristic of autism is hampered communication, repetitive behavior and impaired social communication.
There have been many theories for the cause of autism but there have been no satisfactory, scientifically proven causes. Genetic factors are thought to play a very significant role since research on identical twins show that identical twins have a higher rate of autism than non-identical twins when one of the twins has autism. Another culprit suspected to cause autism is exposure to birth-defect inducing agents as well as the mercury present in the preservatives used in some vaccines but there is no reliable proof of these suspicions.
Autism displays itself over a very wide spectrum from those that are suffering from a very severe case and appear to be mentally disabled and totally dysfunctional to those who have such mild manifestations as to be unnoticed. Another criterion for segregating autistics is by dividing the affected people into Low Functioning Autism (LFA) and High Functioning Autism (HFA). This division of people suffering from autism is based on certain factors like whether their Intelligence Quotient (IQ) is less than (LFA) or greater than HFA) 70.
People with autism have problems socially interacting with people and find it difficult to understand the other person's feelings. This lack of social interaction is visible even in childhood when the infant does not smile or look at other people as much as neurotypical children do. Children with autism do not exhibit much social understanding and do not imitate or respond to social stimulus as much as typical children. Most of their communication is non-verbal and they may experience difficulty understanding or assimilating the concept of 'taking turns' at the swings or other activities.
A number of people with autism exhibit repetitive movements like hand-flapping or head rolling, compulsive behavior like always insisting on arranging objects a certain way only, ritualistic behavior like having foods in the same order (bread before soup followed by cheese, for example) and self injury (mostly by head-banging).
Autism has no known medicinal cure though small doses of anti-depressant drugs have been used in some cases.