106 What Causes ASD?

ASD equally affects people of all races, ethnicities, social classes, lifestyles, and educational backgrounds. Despite the high occurrence, we do not know all the causes of ASD. Most researchers believe that there are probably many causes and variations of ASD with different genetic, biological, and environmental issues at play.

Current research indicates that 10 or more genes on different chromosomes may play varying roles in an individual’s increased susceptibility to ASD. Increased susceptibility means someone with certain genes is more likely to have ASD and may also influence the development or severity of certain symptoms related to ASD and other comorbid disorders.

We know that if a parent has a child with ASD, they have a 2-8% chance of having another child with ASD. We also know that some drugs taken during pregnancy have been associated with ASD, including thalidomide and valproic acid. Brain imaging studies have found differences in the brain structure of individuals with ASD compared to those without. Additional research has shown that environmental factors, such as viruses, may play a role.

While some researchers are examining genes and environmental factors, others are investigating possible neurological, infectious, metabolic, and immunologic factors. Due to the complexity of ASD and the uniqueness of each individual, ASD is likely the result of many interrelated factors (Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, DHHS, 2005).