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Causes of ASD

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Although there is no known unique cause of ASD, there is growing evidence that autism can be caused by a variety of problems.
There is some indication of a genetic influence in autism. For example, there is a greater likelihood that two monozygotic twins (i.e., identical twins) will have autism than two dizygotic twins (i.e., fraternal twins). In the case of monozygotic twins, there is a 100% overlap in genes; whereas in dizygotic twins, there is a 50% overlap in genes, the same overlap as in non-twin siblings. Currently, a great deal of research has focused on locating the 'autism gene' however, many researchers speculate that three to five genes will likely be associated with autism.
There is also evidence that the genetic link to autism may be a weakened or compromised immune system. Other research has shown that depression and/or dyslexia are quite common in one or both sides of the family when autism is present.
There is also evidence that a virus can cause autism. There is an increased risk in having an autistic child after exposure to rubella during the first trimester of the pregnancy. Cytolomegalo virus has also been associated with autism.
There is growing concern that toxins and pollution in the environment can also lead to autism.
There is growing evidence that the gut or intestinal tract of autism children is impaired. Researchers have documented yeast overgrowths (candida albicans), low levels of phenylsulfur transferase, and measles virus in their intestinal tract.
It has been a certain concern that viruses associated with vaccinations, such as the measles component of the MMR vaccine and the pertussis component of the DPT shot may cause autism. A large study conducted by the Danish Epidemiology Science Center and other partners on a large Danish sample of 2 129 864 person-years with a total of 537 303 children included in the cohort a total of follow-up of 5811 children still December 1999. This study provides three strong arguments against a causal relation between MMR vaccination and autism. According to this, as well as other available international studies, the WHO has declared no to be ‘aware of any scientific evidence that meets the criteria laid out by the Committee (The Global Advisory Committee on Vaccine Safety) that might substantiate an association between autism and MMR vaccines’.
With respect to biochemistry, many autistic individuals have elevated levels of serotonin in their blood and cerebral spinal fluid, whereas others have relatively low levels of serotonin. It should be mentioned that other disorders, such as Down syndrome, attention deficit/hyperactivity disorder, and unipolar depression are also associated with abnormal levels of serotonin. There is also evidence that some autistic individuals have elevated levels of beta-endorphins, an endogenous opiate-like substance in the body. It is felt that those individuals who have an increased pain tolerance may likely be due to elevated levels of beta-endorphins.
A dysfunctional immune system has also been associated with autism. It is thought that a viral infection or an environmental toxin may be responsible for damaging the immune system.
As mentioned above, there is also evidence of a genetic association to a compromised immune system. Researchers have found that many autistic individuals have a decreased number of helper t-cells which help the immune system fight infection.
Directorate C - Public Health and Risk Assessment, C2 - Health information]

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