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Autism Spectrum Disorders: Causes

At this point, the causes of ASDs remain unknown, and more research needs to be done. It’s likely, according to Dr. Coplan, that genetic factors probably account for the majority of cases of ASDs. In most families with a child on the spectrum, doctors also find a sizeable increase in related disorders such as depression, anxiety disorder and OCD.  Although there has been a lot of talk in the press about possible environmental causes, there is very little evidence to support these theories or fears.  Research has identified a number of genes associated with ASDs, and preliminary studies have found that people with ASDs have irregularities in several regions of the brain or abnormal levels of neurotransmitters in their brains, according to the National Institute of Neurological Disorders and Stroke.  

It’s also known that ASDs are more likely to occur in people who have other medical conditions such as Fragile X syndrome (a genetic condition that involves mental retardation), tuberous sclerosis (a condition in which benign tumors grow on the brain), Down syndrome (a genetic disorder that causes physical abnormalities and delayed mental and social development), Tourette syndrome (a neurological disorder characterized by repetitive, involuntary movements and tics), epileptic seizures, and other chromosomal disorders. And there’s some evidence linking the use of prescription drugs -- such as thalidomide and valproic acid -- during pregnancy with a higher risk of ASDs. Indeed, the critical period for developing ASDs may occur before birth.

Vaccines and Autism

Contrary to what some people believe, poor parenting practices and vaccines do not cause autism spectrum disorders. Some parents are concerned that the MMR vaccine (for measles, mumps, and rubella), in particular, causes autism. This is based, in part, on a famous 1998 research paper by a British researcher, claiming that the MMR vaccine could cause autism. Earlier this year, The Lancet retracted that paper, based on the researcher’s scientific methods and financial conflicts, and the he lost his license in his native UK. Meanwhile, many studies have examined whether there is a relationship between vaccines and autism spectrum disorders, and study after study has found that vaccines are not associated with ASDs.

Thimerosal and Autism

Another concern stems from whether the mercury-based preservative thimerosal (which is no longer used in most vaccines) could cause autism but a thorough review by the Institute of Medicine found no such link. As the National Institute of Child Health and Human Development puts it, “There is no conclusive scientific evidence that any part of a vaccine or combination of vaccines causes autism, even though researchers have done many studies to answer this important question. There is also no proof that any material used to make or preserve the vaccine plays a role in causing autism.”