The cause, or causes, for autism spectrum disorders (ASDs) remain a mystery, though many culprits are being investigated.

Differences in the Brain

Some researchers are focusing on the brain—particularly, its development and function. There are often differences in the size and structure of an autistic person's brain compared to that of someone who does not have an ASD.

According to the National Institute of Mental Health, many parts of the brain play a role in autism. These include the cerebellum, which fine-tunes the human body's movements, and the sections of the brain responsible for emotion.

Neurotransmitters, which aid in communication between the brain and the rest of the body, are also being investigated to see if they somehow contribute to the development of autism.

There are several rare diseases that can cause autism spectrum disorders. Such cases are often referred to as secondary autism, and include the following diseases:

  • tuberous sclerosis
  • fragile X syndrome
  • phenylketonuria
  • congenital infections

Genetic Factors

Researchers are looking at the possibility of differences in the genetic structure and at hereditary links in families. Family studies have demonstrated that autism is more common in siblings of an autistic child than in the population in general. This suggests that there is a genetic contribution to the development of disease.

Common Misconceptions

Thimerosal, a mercury-based preservative, used in vaccinations in the past, has also been suspected of causing autism spectrum disorders (ASDs).

Despite many well-designed studies, there still remains inadequate research to link mercury-containing vaccines with the development of ASDs. Thimerosal has not been used in vaccinations in the United States since 1999, therefore limiting exposure in children to thimerosal.

A 2010 study by the Centers for Disease Control and Prevention (CDC) stated that “prenatal and infant exposure to vaccines and immunoglobulins that contain thimerosal does not increase risk for autism spectrum disorder (ASD).”

There have been several worldwide studies to determine if the MMR vaccine—important for preventing potentially lethal cases of the measles—is associated with ASDs. A 1998 article in The Lancet suggested a possible relationship between the vaccine for measles, mumps, and rubella and the development of ASDs. Six years later, The Lancet published a retraction, stating no connection between the MMR vaccine and autism.