Autism is a terrible disease with no known cure.
Do you know how many people are affected with it?
Not precisely, but  Autism is caused by both genetic and environmental factors.
how is it caused by enviromental factors?
In some cases, autism is associated with agents that cause birth defects.
I have heard different chemicals such as those in plastic can cause autism.
Causes of autism
Many causes of autism have been proposed, but understanding of the theory of causation of autism and the other autism spectrum disorders (ASD) is incomplete. Research indicates that genetic factors predominate. The heritability of autism, however, is complex, and it is typically unclear which genes are involved. In rare cases, autism is associated with agents that cause birth defects. Many other causes have been proposed, such as childhood immunizations, but numerous epidemiological studies have shown no scientific evidence supporting any link between vaccinations
brain, whereas schizophrenia involves maternally expressed genes and undergrowth.
Proposed models Environmental interactions.
Though autism's genetic factors explain most of autism risk, they do not explain all of it. A common hypothesis is that autism is caused by the interaction of a genetic predisposition and an early environmental insult. Several theories based on environmental factors have been proposed to address the remaining risk. Some of these theories focus on prenatal environmental factors, such as agents that cause birth defects; others focus on the environment after birth, such as