Global Blood Therapeutics Inc. is studying an experimental treatment for sickle cell disease, an inherited disorder that causes red blood cells to become misshapen and leads to blocked blood vessels, causing severe pain and eventually organ failure and death. The National Institutes of Health says a stem cell transplant from a donor is the only cure for the condition, but most patients are too old for a transplant or don't can't find a good enough genetic match. Bluebird Bio Inc., which went public in 2013, is studying a potential gene therapy for the condition, while Bellicum Pharmaceuticals Inc., which had its IPO in December, is studying a drug designed to reduce the side effects of stem cell transplants.