What Causes Autism?
Experts are still uncertain about all the causes of autism. In all likelihood, there are multiple causes – rather than just one. It appears to be that a number of different circumstances — including environmental, biologic, and genetic factors – set the stage for autism and make a child more likely to have the disorder.
There is reason to believe that genes play a major role in the development of autism. It has been found that identical twins are more likely to both be affected than twins who are fraternal (not genetically identical). In a family with one autistic child, the chance of having another child with autism is about 5 percent – or one in 20 – much higher than in the normal population.
Sometimes, parents or other relatives of an autistic child have mild social impairments (such as repetitive behaviors and social or communication problems) that look very much like autism. Research also has found that some emotional disorders (such as manic depression) occur more often in families of a child with autism.
At least one group of researchers has found a link between an abnormal gene and autism. The gene may be just one of three to five or more genes that interact in some way to cause the condition. Scientists suspect that a faulty gene or genes might make a person more likely to develop autism when there are also other factors present, such as a chemical imbalance, viruses or chemicals, or a lack of oxygen at birth.
In a few cases, autistic behavior is caused by:
In the past several years, there has been interest in a theory that suggested a link between autism and the use of thimerosal, a mercury-based preservative used in the measles-mumps-rubella (MMR) vaccine. Although mercury is no longer found in childhood vaccines in the United States, some parents still have concerns about vaccinations.
However, many well-done, large-scale studies have now been performed that have failed to show a link between thimerosal and autism. A panel from the Institute of Medicine is now examining these studies. The reports include a large Danish study that concluded that there was no causal relationship between childhood vaccination using thimerosal-containing vaccines and the development of an autism spectrum disorder and a U.S. study looking at exposure to mercury, lead, and other heavy metals. Both the American Academy of Pediatrics and the Centers for Disease Control and Prevention asert that there is no link between autism and the MMR vaccine or any other vaccine.
Other potential causes of autism are environmental toxins, including pesticides and heavy metals such as mercury. Heavy metals are certainly more commonly encountered in the environment now than they were in the past. It may be that people with autism or those at higher risk for developing it are more sensitive than others to these toxins.
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