What Causes Autism?
Researchers are working steadily to discover the causes of the autism, but because PDD symptoms vary greatly from one affected individual to the next, it is difficult to pinpoint the exact origins of disorders on the spectrum. Here are several theories being investigated.
Autism Theory 1: Genes
While researchers so far have been unable to determine the exact cause(s) of autism, there is evidence that genetics play a significant role. According to the NIH, studies involving twins and families of autistic patients suggest that some may be genetically predisposed to autism. In studies with identical twins, there is a 90 percent chance that if one twin is affected by ASD, the other twin will also be affected. Rates of autism are higher in siblings of children with autism, as well, with reported incidence between 1 in 10 and 1 in 50. Compared to the rate of autistic disorder in the general population, which ranges between 1 in 800 and 1 in 1,000, data like this suggests that there may be a genetic basis for the disorder.
Autism Speaks, a large, nationwide advocacy organization, is leading the Autism Genome Project to map the genes and genetic mutations that may contribute to an autism spectrum disorder. The initiative has already yielded genetic clues that may lead to new autism treatments in the future.
Autism Theory 2: Environment
Since autism diagnoses have risen so dramatically in recent years, many parents suspect an environmental cause. Theories about what that environmental trigger might be include rainy climate, certain medications taken during pregnancy and fragrances, shampoos, nail polish, and cosmetics used during pregnancy, and air pollution. Dr. Harvey Karp is one of a group of doctors investigating whether household chemicals cause autism, but none of these environmental theories has been proven so far.
Autism Theory 3: Birth Spacing
Could the timing between pregnancies raise a child’s risk for autism? A January 2011 study published in the journal Pediatrics suggested that it might. Out of a sample of half a million California children, researchers found that children born fewer than two years after their older sibling were significantly more likely to be diagnosed with autism than those who were born at least three years after their older brother or sister.
One possible reason for the correlation, say researchers, is that the body is low in certain nutrients like folate after pregnancy, and moms who quickly get pregnant again may not have sufficient supplies for the next time around. Another possible explanation is that parents are better able to monitor differences between siblings who are close in age. Speech delays and other ASD symptoms could be more apparent in a child when parents who just witnessed an older, non-ASD sibling at the same age.
Autism Theory 4: Premature Birth
In a 2008 study released by the American Academy of Pediatrics, researchers found that low birth weight and preterm birth (earlier than 33 weeks gestation) were linked to a doubled risk for autism, with the chances of developing ASD somewhat higher for infant girls than boys. However, the study found that the increased risk for autism was also connected to an increased risk for other developmental disabilities, such as mental retardation. According to the study, low birth weight and early gestational age did not increase the risk for autism alone.
Autism Theory 5: Educated Parents
A UC Davis study released in 2010 found a surprising correlation between kids with autism and parents with above-average levels of education. But don’t tear up your Ph.D. just yet – the link between educated parents and autistic kids doesn’t mean that one causes the other. Studies such as these imply that social factors may affect a diagnosis of ASD. Educated parents could have more awareness of the disorder and better access to treatment. According to the NIH “family income, education, and lifestyle do not seem to affect the risk of autism.”
Autism Theory 6: Vaccines
Childhood vaccination became a hot-button topic in the autism community in 1998, when a study published in the respected medical journal The Lancet suggested a correlation between thimerosal, a mercury-based preservative found in vaccines, and the development of autistic symptoms. The study led panicked parents to refuse vaccinations for their children, despite CDC warnings that not immunizing children could lead to outbreaks of serious diseases like whooping cough and measles. Multiple studies have since been published that find no connection between autism and vaccines, and it was later discovered that researcher Andrew Wakefield fabricated the results of the original study.
The National Institute of Health explicitly states that the small amounts of mercury present in vaccines do not make children susceptible to ASD. The American Academy of Pediatrics agrees that thimerosal in vaccines is not linked to the increased rates of autism in the United States and concludes that the benefits of early childhood vaccination are greater than the potential risks.