The animated videos in NORD’s Rare Disease Video Library provide brief introductions to rare disease topics for patients, caregivers, students, professionals and the public. NORD collaborates with medical experts, patient organizations, videographers and Osmosis to develop the videos, which are made possible by individual donations, educational grants and corporate sponsorships. NORD is solely responsible for the content.
Primary myelofibrosis (PMF) is a rare bone marrow disorder that is characterized by abnormalities in blood cell production (hematopoiesis) and scarring (formation of fibrous tissue) within the bone marrow. Bone marrow is the soft, spongy tissue that fills the center of most bones. Bone marrow contains specialized cells called hematopoietic stem cells that grow and eventually develop into one of the three main types of blood cells: red blood cells, white blood cells or platelets. In primary myelofibrosis, a change in the DNA of a single hematopoietic stem cell causes the abnormal cell to continually reproduce itself. Eventually, these abnormal cells crowd out normal, healthy cells in the marrow and, along with scarring within the marrow, disrupt the production of red and white blood cells and platelets.
The symptoms associated with primary myelofibrosis vary and are related to the abnormalities affecting blood cell production. Affected individuals may not have symptoms at the time of diagnosis (asymptomatic) may remain symptom-free for many years. Eventually, affected individuals may develop fatigue, fever, frequent infections, pale skin, night sweats and unexplained weight loss. An enlarged (spleen) is a common finding. An enlarged liver (hepatomegaly) may also occur.
In approximately 50 percent of patients, a mutation of the JAK2 gene has been detected. The exact role this abnormal gene plays in the development of the disorder is unknown.
Primary myelofibrosis belongs to a group of diseases known as the myeloproliferative neoplasms (MPNs). This group of disorders is characterized by the overproduction (proliferation) of one or more of the three main blood cell lines – red or white blood cells or platelets. Three other disorders are commonly classified as MPNs: chronic myeloid leukemia, essential thrombocythemia and polycythemia vera. Myelofibrosis may occur as a secondary characteristic of polycythemia vera or essential thrombocytyemia. Because the MPNs are characterized by uncontrolled cell growth, they may also be classified as blood cancers.