There are many myths about medicine these days. Some are harmless, but many can lead to all sorts of problems. One very harmful medical myth is the idea that autism is caused by childhood vaccination. Although many careful studies have demonstrated that there is just no link between vaccines and autism, you can still find many websites that try to argue that vaccination causes autism. A while back, I participated in a debate hosted by one such website.
In the debate, I discussed and explained the studies that show there is simply no link between vaccines and autism. I also pointed out that some of the authors involved in these studies have a proven track record for finding a link between a vaccine and a serious medical condition, so it is hard to believe that they would miss a link between vaccines and autism if there is one. Not surprisingly, the website that hosted and heavily promoted the debate removed all mention of it afterwards, because the debate clearly showed the error of the idea they they are trying to promote.
Fortunately, real scientists are searching for the actual cause of autism, and lots of progress has been made. I recently ran across a study that addresses autism and the health of the mother during pregnancy. As a result of that study, I learned about a very interesting program that was started in 2003 and is just beginning to produce some very interesting results. It is called the Childhood Autism Risks from Genetics and the Environment (CHARGE) study. The study recognizes that there seem to be both genetic and environmental risk factors for autism, and it is designed to produce rigorous research that will help us understand both.
The CHARGE study has already produced at least three very important and somewhat surprising results.
The first important study compared 304 autistic children to 259 control children that seemed to be developing normally. The researchers had a detailed history of where the mothers lived during pregnancy. What they found was that when mothers lived within one-quarter mile of a freeway at the time of delivery, the child was about 86% more likely to be autistic. More importantly, if the mother lived within one-quarter mile of a freeway throughout the third trimester of her pregnancy, the child was more than twice as likely to be autistic. Interestingly enough, this relationship disappeared if the mother was more than one-quarter mile away from a freeway, and it exists only for freeways, not other kinds of major roads.1
The second important study dealt with prenatal vitamins. When parents plan to have a child, a doctor will often recommend that the mother start taking prenatal vitamins before she becomes pregnant. That way, her body is prepared for the baby that she hopes will be conceived. The study looked at 288 children who had autism, an additional 141 diagnosed with autism spectrum disorder (ASD), and 278 control children who seemed to be developing normally. It found that if a mother started taking prenatal vitamins before she got pregnant, she was 62% less likely to have an autistic child. In addition, they looked at specific genetic anomalies related to metabolism. They found that when the mother had specific genetic anomalies and did not take prenatal vitamins before pregnancy, she was up to 4.5 times more likely to have an autistic child. If the child had one specific genetic anomaly and the mother did not take prenatal vitamins before pregnancy, the child was more than 7 times more likely to have autism or ASD.2
The most recent study (the one that made me aware of the CHARGE data to begin with) looked at the relationship between three metabolic conditions (diabetes, hypertension, and obesity) in the mother and the child’s chance of having autism. It examined 517 children with autism or ASD, 172 children that were otherwise developmentally disabled, and 315 control children that seemed to be developing normally. It found that if the mother was obese, she was 67% more likely to have a child with autism or ASD and nearly twice as likely to have a child with any developmental disorder. Mothers with diabetes were also 67% more likely to have a child with autism or ASD. Hypertension seemed to have an effect as well, but it wasn’t strong enough to be measured with the number of children studied.3
So what does all this all mean? Well, first it’s important to note that none of these studies show that living near a highway, lack of prenatal vitamins, or metabolic conditions cause autism or ASD. They simply show that autism and ASD are correlated with these conditions. Nevertheless, these correlations do raise some interesting possibilities. The first study I discussed references other studies that show that freeway-related pollution tends to dissipate to background levels more than one-quarter of a mile away from the freeway. That means their results indicate that exposure to air pollution during pregnancy (especially in the third trimester) might be one cause of autism.
The second and third studies raise the possibility that autism is related to metabolism. A lack of prenatal vitamins before pregnancy made all mothers more likely to have autistic children, but the chance rose even more when the mother had a metabolic genetic anomaly. Also, the fact that diabetes and obesity in the mother are correlated with autism or ASD adds further weight to the metabolic link. However, it’s clearly not all about the mother. Remember, the most significant chance of having an autistic child came when the child had a metabolic genetic anomaly and the mother didn’t take prenatal vitamins before she conceived.
The bottom line is that both genetics and environment play a role in autism. In addition, researchers should start focusing on metabolic conditions (both genetic and otherwise), as they seem to be important.
1. Volk HE, Hertz-Picciotto I, Delwiche L, Lurmann F, and McConnell R., “Residential proximity to freeways and autism in the CHARGE study,” Environmental Health Perspectives 119(6):873-877, 2010
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2. Schmidt RJ, Hansen RL, Hartiala J, Allayee H, Schmidt LC, Tancredi DJ, Tassone F, and Hertz-Picciotto I., “Prenatal vitamins, one-carbon metabolism gene variants, and risk for autism,” Epidemiology 22(4):476-85, 2011
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3. Krakowiak P, Walker CK, Bremer AA, Baker AS, Ozonoff S, Hansen RL, and Hertz-Picciotto I., “Maternal metabolic conditions and risk for autism and other neurodevelopmental disorders,” Pediatrics 129(5):e1121-8, 2012
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