Scientists don't know exactly what causes autism. Autism was first described in the 1940s, but very little was known about it until the last few decades. Even today, there is a great deal that we don't know about autism.
Because the disorder is so complex and no two people with autism are exactly alike, there are probably many causes for autism.
A great deal of evidence supports the idea that genes are one of the main causes of ASD. More than 100 genes on different chromosomes (pronounced KROH-muh-sohmz) may be involved in causing ASD, to different degrees.
People with autism have slight changes, called mutations (pronounced myoo-TEY-shuhnz), in many of these genes. However, the link between genetic mutations and autism is complex:
This evidence means that different genetic mutations probably play different roles in ASD. For example, certain mutations or combinations of mutations might:
If someone is susceptible to ASD because of genetic mutations, then certain situations might cause autism in that person.
For instance, an infection or contact with chemicals in the environment could cause autism in someone who is susceptible because of genetic mutations.1 However, someone who is genetically susceptible might not get an ASD even if he or she has the same experiences.2
Researchers are also looking into biological factors other than genes that might be involved in ASD. Some of these include:
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