Myelodysplastic syndromes (MDS) are a family of rare disorders in which the bone marrow fails to make enough healthy red blood cells, white blood cells or platelets. This is caused by bone marrow producing lots of underdeveloped, or immature, cells that have an abnormal shape, size or look. These are called blast cells. Most experts agree that MDS is a form of blood and bone marrow cancer.
Paroxysmal nocturnal hemoglobinuria (PNH) is an ultra-rare bone marrow failure disease in which red blood cells break apart. Normal red blood cells have a shield of proteins that protect them from coming under attack by the body's own immune system. PNH occurs because that protein shield is missing. PNH is often associated with reduced bone marrow function (low blood counts) caused by aplastic anemia.