Rare Blood Disorders: About Rare Blood Disorders

When the normal process of blood cell growth and development breaks down, certain cell types can be produced in abnormally large quantities or in abnormal form. This gives rise to blood cancers or other blood disorders.

The most common blood cancers include leukemias, lymphomas, and multiple myeloma. Less common or “rare” blood disorders include various myeloproliferative diseases (also called myeloproliferative neoplasms) as well as histiocytosis and paroxysmal nocturnal hemoglobinuria (PNH).

Myeloproliferative Diseases

Normally, the bone marrow makes blood stem cells (immature cells) that become mature blood cells over time. A blood stem cell may become a myeloid stem cell or a lymphoid stem cell. A myeloid stem cell becomes one of three types of mature blood cells: red blood cell, white blood cell, or platelet. A lymphoid stem cell becomes a white blood cell.

With myeloproliferative diseases, too many of certain types of blood cells are made in the bone marrow, the spongy tissue inside the large bones in the body.

The type of myeloproliferative disorder that develops is based on whether the body is making too many red blood cells, white blood cells, or platelets. Sometimes the body will make too many of more than one type of blood cell, but usually one type is affected more than the others.

There are several kinds of myeloproliferative disease, including polycythemia vera, myelofibrosis, essential thrombocythemia, mastocytosis, and eosinophilia.

Other Rare Blood Disorders

In addition to myeloproliferative diseases, we treat a spectrum of other rare blood disorders at Memorial Sloan Kettering, such as histiocytosis, which is characterized by the presence of an abnormally high number of white blood cells called histiocytes, and paroxysmal nocturnal hemoglobinuria, in which red blood cells break down earlier than normal.