There is no single cause of autism spectrum disorder. Although the disorder is not completely understood, research suggests that it can develop from genetic and nongenetic influences. Scientists have discovered that certain genetic variations are more common in people diagnosed with autism. These changes in genes increase the risk—but do not guarantee—a child will develop autism.
Other risk factors that increase the likelihood that a child will develop ASD include:
Having a sibling with autism
Having older parents
Prenatal exposure to air pollution or to certain pesticides
Maternal obesity, diabetes, or immune system disorders
Extreme prematurity or low birth weight
Problems during the process of birth which cause periods of oxygen deprivation
The presence of certain genetic conditions, such as Down syndrome, Fragile X, or Rett syndrome