causes of autism causes of autism many causes of autism have been proposed, but understanding of the theory of causation of autism, or otherwise known as autism spectrum disorder (asd) is incomplete. attempts have been made to incorporate the known genetic and environmental causes into a comprehensive causative framework. asd is a complex developmental condition marked by persistent challenges to social interaction, speech and nonverbal communication, and restricted/repetitive behaviors and its phenotypes vary significantly. this diagram shows the brain sections and how autism relates to them. 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. numerous epidemiological studies have shown no scientific evidence supporting the controversial but popular theory that autism is caused by vaccines. background main article: autism autism involves atypical brain development which often becomes apparent in behavior and social development before a child is three years old. it can be characterized by impairments in social interaction and communication, as well as restricted interests and stereotyped behavior, and the characterization is independent of any underlying neurological defects. other characteristics include repetitive-like tasks seen in behavior and sensory interests. this article uses the terms autism and asd to denote classical autism and the wider dispersion of symptoms and manifestations of autism, respectively. autism's theory of causation is incomplete. it has long been presumed that there is a common cause at the genetic, cognitive, and neural levels for autism's characteristic triad of symptoms. however, there is increasing suspicion among researchers that autism does not have a single cause, but is instead a complex disorder with a set of core aspects that have distinct causes, where the interactions between these core aspects determine whether or not autism develops. different underlying brain dysfunctions have been hypothesized to result in the common symptoms of autism, just as completely different brain types result in intellectual disability. the terms autism or asds capture the wide range of its processes at work. although these distinct causes have been hypothesized to often co-occur, it has also been suggested that the correlation between the causes has been exaggerated. the number of people known to have autism has increased dramatically since the 1980s, at least partly due to changes in diagnostic practice. it is unknown whether prevalence has increased as well. the consensus among mainstream autism researchers is that genetic factors predominate. environmental factors that have been claimed to contribute to autism or exacerbate its symptoms, or that may be important to consider in future research, include certain foods, infectious disease, heavy metals, solvents, diesel exhaust, pcbs, phthalates and phenols used in plastic products, pesticides, brominated flame retardants, alcohol, smoking, and illicit drugs. among these factors, vaccines have attracted much attention, as parents may first become aware of autistic symptoms in their child around the time of a routine vaccination, and parental concern about vaccines has led to a decreasing uptake of childhood immunizations and an increasing likelihood of measles outbreaks. however, there is overwhelming scientific evidence showing no causal association between the measles-mumps-rubella (mmr) vaccine and autism, and there is no scientific evidence that the vaccine preservative thiomersal causes autism. genetics main article: heritability of autism