What causes autism and autism spectrum disorders

Until recently, these disorders were thought to be caused by genetic factors, but recent research shows that environmental factors are equally important. What is unlikely is that there is one specific gene that is responsible for the development of this disorder. It is more likely that several genes combine and act together. Although many link autism to gastrointestinal disorders, studies have found no evidence of an increased incidence of gastrointestinal disorders in children with autism. 

Differences in the structure of brain tissue have been noticed in a certain number of children since the earliest age. It was found that brain size increased significantly more during the first years of life in children with autism compared to children of typical development. So different parts of the brain did not communicate typically. However, in children with autism at the age of 10-15, the average brain size is similar to the brain size of children without developmental disabilities, while later in adulthood there is a tendency to reduce the volume of gray and white mass in people with autism. 

A large amount of evidence from various studies indicates that we must not forget the role of maternal and postnatal immune dysregulation in the development of autism. 

Environmental factors that may be associated with autism include: exposure to environmental pesticides, viruses (chickenpox, rubella), retinoic acid, use of certain drugs in pregnancy, alcohol use during pregnancy, age of parents, complications in childbirth associated with trauma or ischemia and lack of oxygen. 

There is no proven link between vaccines and the development of autism.