EZRA KLEIN is at a health-issues conference where he's hearing some interesting counter-counter-intuitive things about the future impact of the codification of the human genome on medicine. As it turns out, it's going to be a big deal after all. The main effect of genomics on medicine is a growing ability to tailor treatments to individual patients. Very promising. But as Mr Klein writes, it threatens to lead to "an explosion in health inequality":

Right now, health inequality, though significant, is moderated by the fact that the marginal treatments that someone with unlimited resources can access simply don't work that much better than the treatments someone with more modest means can access. In some cases, they're significantly worse. In most cases, they're pretty similar, and often literally the same.

But as those treatments begin to work better, and as we develop the ability to tailor treatments to individuals, we should expect that someone who can pay for the best treatments for their particular DNA sequences to achieve far better health-care outcomes than someone who can't afford the best treatments and has to settle for general therapies rather than individualized medicine.

I'd come at this issue a bit differently. The reason individualised treatment is likely to entail inequality, I'd bet, isn't so much the expense; that would be true of any hot new hi-tech treatment. Rather, it's that we're going to increasingly know who is or isn't likely to respond to treatment, and we may often know this in advance. For instance, genomics is already having a significant impact on breast-cancer treatment: by analysing the DNA of both the patient and the cancer cells, doctors can now identify 25% of cases which won't respond to standard chemotherapy. That's great; it saves money and needless suffering. But to the extent that a result like this is based on a patient's genetic profile, the cost effects can be predicted in advance and passed through to insurance premiums. Are you a first-line chemotherapy responder? Your premiums are cheaper. Or perhaps more expensive; if you do get cancer, you'll live longer, racking up more bills...

The point is that individualised medicine breaks down some of the egalitarian presumptions that lie behind health insurance. Part of the logic behind insurance is that it's a risk pool; none of us knows when we're gonna go, so we agree to split the costs. But genetic profiling may increasingly give each of us our own set of pre-existing conditions, good or bad. And that may test people's willingness to chip in for the health costs of their fellow-citizens. When "it coulda been me" turns into "nope, it couldn't", we may start seeing...hm, I was about to say "a breakdown in social solidarity", but then I remembered we're talking about America here. How about "even less willingness to do anything for people who aren't as lucky as you are."