Causes of Autism - Autism and Related Disorders

Autism and Related Disorders

Autism involves abnormalities of brain development and behavior which become apparent before a child is three years old and have a steady course with no remission. It is 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. It is part of a larger family called autism spectrum disorders (ASD) or pervasive developmental disorders (PDD), which include closely related disorders such as Asperger syndrome and PDD-NOS. This article uses autism to denote the classical autism and ASD to denote the wider family.

Autism's theory of causation is still 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. In other words, completely different underlying brain dysfunctions have been hypothesized to result in the common symptoms of autism, just as completely different brain problems result in mental retardation. The term "the autisms" or "the ASDs" captures the wide range of disease 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. By 2008, the CDC's estimate for ASD prevalence was stated at 11.3 per 1000 (1 in 88) children.

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 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, illicit drugs, and vaccines. 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 vaccine and autism], and there is no scientific evidence that the vaccine preservative thiomersal helps cause autism.