So does that mean cancer patients should be suing cows?

I’m currently working on what is meant to be a short piece about the “science” of autism — i.e., what we think we know and why we think we know it. I say meant to be a short piece because it’s proving very difficult to summarize the current landscape accurately while keeping word count to a minimum: When you’re dealing with the early stages of a scientific research, it’s well nigh impossible to be simultaneously accurate and concise. (After all, if preliminary research didn’t have caveats, it wouldn’t be preliminary.)

Take, for example, a July report about potential links between prenatal exposure to SSRI’s and autism spectrum disorders. The study, which was based on analysis of patients in the Kaiser Permanente Medical Care Program in Northern California, reached the following conclusion:

Although the number of children exposed prenatally to selective serotonin reuptake inhibitors in this population was low, results suggest that exposure, especially during the first trimester, may modestly increase the risk of ASD. The potential risk associated with exposure must be balanced with the risk to the mother or fetus of untreated mental health disorders. Further studies are needed to replicate and extend these findings.

In their public statements, the authors were equally circumspect. That’s wholly appropriate: It could be that the numbers used here will wash out when more studies are done with larger sample sizes. Even if they don’t, the apparent correlation between SSRI use and autism diagnoses doesn’t mean that the two factors are causally linked. I wrote about this at several points in my book:

The difficulty in determining whether correlation equals causation causes an enormous number of misapprehensions. Until a specific mechanism demonstrating how A causes B is identified, it’s best to assume that any correlation is incidental, or that both A and B relate independently to some third factor. An example that highlights this is the correlation between drinking milk and cancer rates, which some advocacy groups (including People for the Ethical Treatment of Animals) use to argue that drinking milk causes cancer. A more likely explanation is that cancer diagnoses and milk consumption both have a positive correlation with increased age: On average, milk drinkers live longer than non-milk drinkers, and the older you are, the more likely you are to develop cancer. This does not, however, mean that drinking milk actually causes people to live longer: It could be that people who drink milk have better access to high-quality health care or eat more healthily than people who do not drink milk.

As more research is conducted in the months and years to come, perhaps we’ll discover that women who are prescribed SSRIs while pregnant are more likely to be pro-active about seeking diagnoses for their children…or maybe we’ll learn that whatever it is that causes some women with depression to respond positively to SSRIs is also the reason their children have a slightly higher chance of being diagnosed with autism. Who knows?

The media coverage of the July paper was, on the whole, appropriately cautious. (Perhaps some lessons were learned from the MMR fiasco after all!) As Sullivan points out on Left Brain/Right Brain, however, not everyone is being so judicious: “Here we are, two months later, and what do I find in a recent Google search? A nice big ad for attorney’s looking to build a class action lawsuit.”


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One Response to So does that mean cancer patients should be suing cows?

  1. Tired of the woo says:

    Looking forward to your article! Finished your book a couple of weeks ago (as did my 12 yr old daughter with ASD who wants to be a doctor!), and thoroughly enjoyed it.

    What this study probably reflects is the genetic link between depression (and other mood disorders) and autism. It’s pretty well known that autism is more common in families where there are mental disorders of various types–especially bipolar disorder, but also OCD, anxiety disorders and major depression.

    To make the case that it’s actually the drug contributing to autism, they would need a large group of pregnant moms with untreated depression to compare with these SSRI-taking moms. I haven’t read the study yet, so it’s possible that they did do that.