I would just add that, as Dr. Menon says, different countries take different approaches. In Australia and New Zealand, for instance, they actually vet drugs that are for rare/orphan diseases through their centralized process, but they also have, under political pressures, probably rightfully in some cases, created separate funding envelopes for drugs for rare diseases. I think that owing to the unique ethical considerations and social responsibilities that we may have related to some of these conditions, you might argue for a national silo of funding, earmarked and capped in terms of budget, from which you would make a decision about rare diseases, using a slightly different algorithm with respect to cost-effectiveness.
I still believe that the phrase “globalize the evidence, localize the decision” should hold. These drugs should be subject to the same rigorous standards of proof. What we don't want to be doing is buying promise, hope, or hype. We want to be purchasing health outcomes here, and so we want to know whether these drugs work. In this context I believe “globalize the evidence, localize the decision” should begin to be taken literally. Oftentimes there are not enough patients in a given country to actually properly assess those drugs in one country, so we should be looking to partnerships with our colleagues around the world to figure out how we can develop the best possible approach to being ethical and responsible about these products and patients, showing compassion while also making sure that we're doing the right thing in terms of buying appropriate outcomes.