During the early development of autism research, the causes for autism were thought to be a result of "nurture," a result of cold and distant parenting, a.k.a. the "refrigerator mother" theory in 1950s. However, in the 1970s, a study on autistic twins found that if one twin had autism, the other twin was also very likely to have autism too, which led to the rise in the belief that autism is actually a result of genetic or "nature" factors, and not due to poor parenting. Currently, there are still no definite causes of autism. Nevertheless, as autism researches expand both the depth and the breadth of their knowledge on autism, scientists are discovering several probable causes. Below are some conjectures of what might cause autism:
1. Genes. The Autism Genome Project (AGP), which is currently the largest ongoing study of autism, uses computer technology to track the genome of 1168 families with at least two autistic children. They have discovered that autism is not only suspected of being caused by a single gene, but by many genes located on the 23rd chromosome. The principal investigator of the project has indicated that there is great hope in AGP, because now that the researchers have isolated the genes, they can then begin to focus on the mutations of those genes and how they cause autism. They estimate that in 5 to 10 years, the achievements of AGP will be put into practice to heal or prevent autism. (ABC news, Feb. 18, 2007) Another indicator that links autism to genetics is that autism affects a ratio of 4:1 boys to girls, which is a strong suggestion that autism is a sex-linked genetic trait.
2. Vaccines. One case that occurred in Georgia, USA involved Hannah Poling, a nine-year-old girl who was compensated by the Federal Vaccine Fund for her autism symptoms. In a court document, the government said vaccines aggravated "a rare underlying metabolic condition that resulted in a brain disorder with features similar of autism spectrum disorder."(Fox News, Mar.06, 2008) It is hypothesized that two classifications of vaccines may cause autism: the measles, mumps and rubella (MMR) vaccine, and a mercury-based preservative called thimerosal. However, this hypothesis has become the most controversial issue in causes of autism. It is disputed by most scientists because there has only been one academic study done in an unscientific way to prove this cause. However, some parents consider this dismissal to be a "conspiracy" of the scientific community to hide the fact that vaccines which contain ethyl mercury do in fact cause autism.
Another popular theory is that neither genetic nor environmental factors alone cause autism, but their reciprocation cause autism to be expressed. That is to say, the environmental factors are like "triggers" to "activate" the autism genes. However, this theory is far from final, and scientists still need more time to work out their theories.
Fox News, "Georgia girl, 9, helps link vaccines to autism cause."
ABC News, "Study Suggests Autism Causes Are Genetic"
Pittsburgh's tribune-review, "Autism's cause unknown, but research points to genetics"
New York Times, "On Autism's Cause, It's Parents vs. Research"