Possible Causes
Causes for autism can be divided into two categories: secondary and idiopathic. In the secondary category the cause of Autism can be attributed to a chromosomal abnormality, an environmental agent, or a single gene. Secondary causes for Autism are found to be the less prevalent of the two causes; only 5-10% of the cases could be identified as being caused by a secondary factor (Reddy 2005). The idiopathic category accounts for cases of autism that can’t be traced to a single gene or abnormality.
Environmental Causes of
Secondary Autism
The environmental causes of autism
have been supported in some studies, but also subject to scrutiny in
others. Some environmental causes
are suggested to be in utero exposures to rubella, valproic acid, thalidomide,
and mercury toxicity. A drawback of some of these studies is that they fail to
place the environmental factor as the causative agent and not a preexisting
genetic abnormality. In the case of mercury toxicity it has been found that
testosterone potentates the toxicity, whereas estrogen is protective of
toxicity. Wakefield et al caused a commotion in the media when they published
an article in 1998 linking autism to the measles-mumps-rubella (MMR) vaccine.
However, no further studies have been able to support
Chromosomal Causes of
Secondary Autism
The possible chromosomal causes of autism are vast. Gillberg reviewed the literature to better document chromosomal disorders associated with autism. Gillberg found literature linking autism to abnormalities on chromosomes 1, 2, 3, 5, 6, 7, 8, 9, 11, 13, 15, 16, 17, 18, 21, 22, X, and Y (1998). Rutter investigated heritability of autism and found that the heritability of underlying autism was greater than 90% (2000). Also, Rutter said that the heritability that was demonstrated was not compatible with a single-gene Mendelian disorder, and boldly suggested that there was anywhere between two and ten genes causing each case of autism.
Idiopathic Causes of Autism
The reason why so many cases of autism are called idiopathic is because with such a diverse number of abnormalities that a particular autistic can have it is hard to contribute the cause to one particular abnormality, or a particular set of abnormalities. Geier and Geier found an attribute in groups of seemingly unrelated autistics that they suggest should be investigated immediately for the treatment of autism (2005). What was found in Geier and Geier’s review was that testosterone played a large role in the manifestation of autistic disorder. When they reevaluated the treatments of a number of previous studies they found that, whereas the epidemiology’s of autism in these studies were dissimilar the treatments all worked to decrease testosterone levels giving improvements in the disorder.