Thursday, November 08, 2007

Genetic Testing for Atrial Fibrillation

It's "Genes Gone Wild."

Trap some Icelanders, swab their cheeks, compare their genes, and make wild predicitions about outcomes. It seems that's all you need these days to tap into the power of fear-based marketing used by genetic testing companies set to bilk gazillion dollars from gullible consumers.

And they'll likely succeed. I mean, after all, what's $200?

In July of this year, a single letter was published in the journal Nature detailing the findings of an "inverse solution" of an Icelandic and Han Chinese population that identified two specific genetic markers from gene 4q25 that suggested a correlation between these genetic markers and the presence of atrial fibrillation. That letter was authored by 19 stake-holders in deCode Genetics (including the principle author), a genetic testing company with more than a minor passing financial interest in performing such testing. They found that 35% of individuals of European descent have at least one of the genetic markers identified and that the risk of atrial fibrillation increases by 1.72 and 1.39 per copy of the gene. The association with the stronger variant was replicated in the Chinese population, where it is carried by 75% of individuals and the risk of atrial fibrillation was increased by 1.42 per copy of the gene. Doctors were even schmoozed to the potential wonders of this testing at the recent American Heart Association meeting. To be sure, it is miraculous what can discovered using their genetic debugging technique these days.

So what does this mean for you and me?

It means that they found a genetic marker that they estimate might be able to identify the development of atrial fibrillation 1.10 years earlier than those in whom the genetic marker is missing.

The deCode company would like to think that they can better target patients who would benefit from prolonged cardiac monitoring after ischemic stroke, but there are no data to support this assumption. The deCode company further believes that their genetic determinant can predict who is at greater risk in the real wide world at developing atrial fibrillation and who might benefit from being on coumadin after a stroke or transient ischemic attack, but again, there are no data to support this claim. The presence of this genetic marker does not mean you can predict if you will develop atrial fibrillation in your lifetime. It does not mean that it can predict if a cardiac monitor will be able to detect any atrial fibrilaltion earlier because you have the gene or not. In short, there are no prospective data regarding the application of the results from this genetic test as a prevention strategy for atrial fibrillation in humans.

What it will do is set you back $200.

You see, their study determined a correlation, but not causation. The two are very different. Just because there is a correlation of the presence of a genetic marker and atrial fibrillation, this correlation does not, in itself, say anything about the cause or etiology of atrial fibrillation in an individual patient.

What the marketing of these tests does do is misinform and confuse the general public as to the potential uses and pitfalls of this technology.


18:10 CST: This just in, another late-breaking trial from the American Heart Association meeting using genetics to determine who will develop out-of-range blood thinning levels (INR's) showed a similar lack of clinical relevance.

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