What Causes Heart Disease? No One Knows

OK, that headline is an exaggeration, but one of the most stunning statistics I've gleaned in the past couple years is that when you put together all the known causes of coronary artery disease - high cholesterol, stress, high blood pressure - you account for something like half of all cases. That's it. In other words, for fully half of all cases of heart disease, we have no idea what the cause is (this comes from UC Berkeley's Len Syme; I'm trying to track down the specific stat he used. If you know, please tell me).

That means that despite all the research that's been done on heart disease, and all the money spent on that research, there's still a massive black unknown spot. On a population level, this means that half of the people who are going to get heart disease have no way of ever knowing it, ever guarding against it, because they simply don't match up with any of the known causes. For a disease that ranks as the number one killer in the US, that's a rather frightening illustration of our still-limited medical knowledge.

The easy assumption, of course, is that there's a massive genetic component at work that simply hasn't yet been discovered. That's what I figured, and many others have as well. But today I read a report about a meta-analysis done in the UK that shows that at least one likely gene - APO E2- may in fact have very little to do with heart disease (the study was published in JAMA last week). One genetic variant did have some associated reduction in risk (20%), but it was a much smaller effect than anticipated, according to the study authors.

This is especially disappointing because there has been some movement towards using screening for APO as a risk factor for heart disease. APO E2 is too rare a mutation to be a worthwhile screen, the authors say (APO E4 is a marker for Alzheimer's Disease).

So where's that leave heart disease? That massive black spot of unknown is still there.