Michael Bromberg, MD, PhD, Chief of the Section of Hematology at Temple University Hospital, offered insight to HealthCentral about paroxysmal nocturnal hemoglobinuria, or PNH, a rare blood disorder that causes the production of defective red blood cells that the immune system destroys in a process called hemolysis. Along with medication, supportive therapies are typically prescribed, and one of the most common is supplementation of folic acid.