Autism Clustered in Affluent Areas: Cross Out Local Environmental Causes
Posted Jan 07 2010 12:43pm
Drinking the local tap water won't cause autism.
Forget about pollution, pesticides, heavy metals and any other enviromental causes particular to where you live. Your choice of neighborhood, town, even city doesn't seem to put your child at risk of autism. Fortunately, we can cross off a slew of suspects - local enviromental exposures - from the list of possible causes of autism.
That's the more exciting conclusion from a huge study out of University of California Davis that looked at the geographical distribution of autism diagnoses for children born between 1996 and 2000. The UC Davis team found about 10,000 autistic children.
The researchers identified 10 autism clusters, communities where autism diagnoses were about 70% more likely to occur than in nearby communities. What distinguised those clusters? In other words, what explained the differing rates of autism between those geographic areas? Not any regional environmental conditions. Those correlations were not significant. So not the local water or pollution, so we can rule those out. Basically, it was the wealth and social status of the parents living there. Autism diagnoses tend to be higher in areas where parents are better educated, white, and older. The clusters were concentrated in Southern California and around San Fransisco.
Not that surprising, really.
Do we think social status or education causes autism? Of course not. I think it's safe to assume parents with more money, degrees, better jobs are more likely to have and use health care services, and no doubt better at working the system, and thus, be more likely to have their children diagnosed. True, older parents (moms and you too, dads) are more likely to have a child diagnosed with autism - independent of other factors.
What about other environmental causes? This study didn't look at widespread factors that wouldn't differ between communities within and outside the clusters (e.g., pollution from traffic) nor those particular to individual households (e.g., drinking non-organic milk).
The study suggests autism may be underdiagnosed in children living outside these cluster, especially minority children from poor families. Or it could also mean white rich kids are overdiagnosed, take your pick, or my guess, some of each. Why care if we overdiagnose? Well, for one, when we're searching for the roots, we have to be clear about what disorder, set of symptoms, we're talking about. If different triggers set off different symptoms, then it does matter. It probably also helps to know the disorder better if we're to successfully treat kids too, though not so much if we're treating symptoms versus the disorder. Knowing the prognosis, the set of challenges children with different symptoms face, must impact the treatment.
It's wise to keep in mind that autism is a complex neurolodevelopmental disorder probably caused by a range of factors, including a sizeable genetic contribution. Whenever I read or hear about "environmental" causes I first think of chemicals and pollution and all the other "green" concerns but this leaves out a lot of factors that might trigger disorders and diseases. Things like prenatal conditions, viruses, nutrition, social relationships and networks. Scientists have a broader notion of "enviromental" - basically anything that isn't genetic.
The other complicating, and quite frankly exciting issue, is our ever-evolving understanding of nature (genes) versus nurture (the enviroment). We used to have a more limited view of the duo - factors were either one or the other. But now we know environmental sources can interact with the genetic expressions of our DNA. They can turn on (or off) our genes so to speak. And evidence from epigenetic studies show behavior and environmental conditions (like diet) can influence the expression of genes in off-spring, even a couple generations later. In rats, anyhow. A grandmother's exposure to a mineral can determine whether her grand-daughter will develop cancer. So even though the grand-daughter has inherited the cancer gene - it can be turned off (conceivably by proteins transmitted along with the cancer genes) by the grandmother's diet.
So it will most likely be a while for us to untangle the triggers of autism. What's more, if the new Diagnostic and Statistical Manual (the bible of offically recognized mental health disorders) drastically changes the Autistic Spectrum, we may have a bigger mess. The American Psychiatric Association is talking about throwing out the spectrum, omitting Asperger's and Pervasive Developmental Disorder in favor of rating the severity of individual symptoms. At the same time, they also might add Sensory Perception Disorder, another complex and varying set of symptoms that share a lot in common with autism.
So I'm guessing a not insubstantial set of children who would have been diagnosed with the more mild autism disorders (esp. Pervasive Developmental Disorder) may get the new SPD label. If that happens, researchers will have one hell of a time trying to find the roots of autism. Retrospective studies will be in a bind. Researchers will have to figure out who had what, separating kids based on symptoms (yes, which often overlap) rather than diagnoses. The autism teams will have to throw out the kids with the more SPD symptoms. I mean, if we really want to get at the roots of autism, differentiating it's causes and treatment, from other disorders. Almost makes me want to get back into the research lab!
And of course, we'll probably also see a drop in autism diagnoses and a rise in Sensory Perception Disorder. So we'll have studies figuring out if the drop in autism can be accounted for by the rise in SPD.
You can find the actual article in the Autism Research journal but you'll have to pay thirty dollars. More than a hard-cover bestseller or a trip to the movie theater with popcorn and a drink. Scientific knowledge costs big these days.