Hemophilia, a disease linked with legends of European monarchs, frail heirs and one flamboyant charlatan called Rasputin, still afflicts many people today.
And the very treatments that can help can also put patients' lives at risk.
The standard treatment is infusion with an expensively produced protein that helps the blood to clot. But in some patients the immune system fights the therapy, and in a subset of those, it sets off an allergic reaction that can result in death.