The True Causes of Autism Spectrum Disorders

"What are the true causes of Autism Spectrum Disorders?  I hear so many different theories from so-called experts, which seem to muddy the waters rather than shed light on the topic. Also, are the rates of ASD increasing as rapidly as the 'experts' say they are?"

This is a very hot topic, because so many people have their own pet theory based on a limited amount of research and hear-say.

Studies measuring Autism Spectrum Disorders (ASD) prevalence (i.e., the number of kids affected by Autism Spectrum Disorders over a given time period) have reported varying results, depending on when and where the studies were conducted and how the studies defined Autism Spectrum Disorders.

In a 2009 government survey on Autism Spectrum Disorders prevalence, the Centers for Disease Control and Prevention (CDC) found that the rate of Autism Spectrum Disorders was higher than in past U.S. studies. Based on health and school records of 8-year-olds in 14 communities throughout the country, the CDC survey found that around 1 in 110 kids have an Autism Spectrum Disorder. However, more recent research suggests that the prevalence rates are much higher than 1 in 110. Males face about four to five time’s higher risk than females (although there is varying opinion of this statistic as well).

Researchers disagree about whether this shows a true increase in Autism Spectrum Disorders prevalence. Since the earlier studies were completed, guidelines for diagnosis have changed. Also, more moms and dads and pediatricians now know about Autism Spectrum Disorders, so they are more likely to take their kids to be diagnosed, and more pediatricians are able to properly diagnose Autism Spectrum Disorders. These and other changes may help explain some differences in prevalence numbers. Even so, the CDC report confirms other recent studies showing that more kids are being diagnosed with Autism Spectrum Disorders than ever before.

Scientists don't know the exact causes of Autism Spectrum Disorders, but studies suggest that both genes and environment play important roles:


In identical twins who share the exact same genetic code, if one has an Autism Spectrum Disorder, the other twin also has it in nearly 9 out of 10 instances. If one child has an Autism Spectrum Disorder, his/her other siblings have 35 times the normal risk of also developing the disorder. Researchers are starting to identify particular genes that may increase the risk for Autism Spectrum Disorders. Still, researchers have only had some success in finding exactly which genes are involved.

Most individuals who develop an Autism Spectrum Disorder have no reported family history of autism, suggesting that random, rare, and possibly many gene mutations are likely to affect an individual's risk. Any change to normal genetic information is called a “mutation.” Mutations can be inherited, but some come about for no reason. Mutations can be helpful, harmful, or have no effect at all.

Having increased genetic risk does not mean a youngster will definitely develop an Autism Spectrum Disorder. Many scientists are focusing on how various genes interact with each other and environmental factors to better understand how they increase the risk of this condition.


“Environment" refers to anything outside the body that can affect one’s health (e.g., the air we breathe, the water we drink and bathe in, the food we eat, the medicines we take, etc.). Environment also includes the child’s surroundings in the womb, when his/her mom's health directly affects growth and earliest development. Researchers are studying many environmental factors (e.g., family medical conditions, parental age and other demographic factors, exposure to toxins, complications during birth or pregnancy, etc.).

As with genes, it's likely that more than one environmental factor is involved in increasing risk for an Autism Spectrum Disorder. And, like genes, any one of these risk factors raises the risk by only a small amount. Most individuals who have been exposed to environmental risk factors do not develop an Autism Spectrum Disorder.

Scientists are studying how certain environmental factors may affect certain genes (e.g., turning them on or off, or increasing or decreasing their normal activity). This process is called “epigenetics” and is providing scientists with many new ways to study how disorders like Asperger’s and High-Functioning Autism develop and possibly change over time.


Doctors recommend that kids receive a number of vaccines early in life to protect against dangerous, infectious diseases (e.g., measles). Since doctors in the U.S. started giving these vaccines during regular checkups, the number of kids getting sick, becoming disabled, or dying from these diseases has dropped dramatically.

Young people in the U.S. receive several vaccines during their first 2 years of life (around the same age that Autism Spectrum Disorder symptoms often appear or become noticeable). A minority of moms and dads suspect that vaccines are somehow related to their youngster's disorder. Some may be concerned about these vaccines due to the unproven theory that Autism Spectrum Disorders may be caused by “thimerosal.” Thimerosal is a mercury-based chemical once added to some vaccines to help extend their shelf-life. However, except for some flu vaccines, no vaccine routinely given to preschool kids in the U.S. has contained thimerosal since 2001. Despite this change, the rate of kids diagnosed with Autism Spectrum Disorders has continued to rise.

Other moms and dads believe their youngster's disorder could be linked to vaccines designed to protect against more than one disease (e.g., the measles-mumps-rubella vaccine), which never contained thimerosal.

Many studies have been conducted to try to determine if vaccines are a possible cause of autism. As of 2010, none of the studies have been able to link autism and vaccines. Following extensive hearings, a special court of Federal judges ruled against several test cases that tried to prove that vaccines containing thimerosal, either by themselves or combined with the MMR vaccine, caused autism.

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