The term “rare blood disorders” describes less common conditions that affect blood cells’ ability to function correctly.

Bone marrow is a spongy substance present in the center of bones. It produces the three main types of cells in blood: red blood cells (RBCs), white blood cells (WBCs), and platelets. RBCs carry oxygen around the body, WBCs help prevent infections, and platelets control bleeding.

Health experts may separate rare blood disorders into two classes:

  • Myeloproliferative disorders cause the bone marrow to produce too many myeloid cells, such as RBCs, platelets, and certain WBCs.
  • Lymphoproliferative disorders cause the bone marrow to produce too many lymphocytes, a type of WBCs.

This article further explores rare blood disorders, explaining the types and treatments.

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Myeloproliferative neoplasms (MPNs) are a group of conditions in which the body produces too many myeloid cells. Experts classify MPNs as a type of blood cancer.

The type of MPN a person has depends on the type of myeloid cells the body is overproducing. In some cases, the body overproduces more than one type of blood cell. However, the condition usually affects one type of blood cell more than others.

MPNs typically result from genetic changes, such as variations in the JAK2 gene. Risk factors can include exposure to radiation or certain chemicals.

According to the National Cancer Institute, there are six types of MPNs.

Chronic myelogenous leukemia

Chronic myelogenous leukemia is a slow-growing cancer in which the bone marrow produces too many WBCs. As it progresses, immature WBCs called myeloblasts build up in the blood and bone marrow and impair the development of other blood cells. This condition is also known as chronic granulocytic leukemia.

Polycythemia vera

Polycythemia vera causes the blood to thicken as a result of having too many RBCs in the bone marrow and blood. It may also increase the number of WBCs and platelets.

This condition can result in bleeding problems and the formation of blood clots in blood vessels.

Primary myelofibrosis

Primary myelofibrosis is a progressive condition in which fibrous tissue replaces bone marrow. As a result, organs such as the liver and spleen make blood instead of the bone marrow.

Other names for this disorder include:

  • chronic idiopathic myelofibrosis
  • agnogenic myeloid metaplasia
  • idiopathic myelofibrosis
  • myelosclerosis with myeloid metaplasia

Essential thrombocythemia

Also known as essential thrombocytosis, this condition results in an increase in platelets, or thombocytes, in the blood. The main cause of essential thrombocythemia is the overproduction of hematopoietic cells due to changes in certain genes, such as JAK2, CALR, and MPL. Hematopoietic cells are cells that can develop into all types of blood cells.

Chronic neutrophilic leukemia

Chronic neutrophilic leukemia occurs when the blood contains too many neutrophils, which are a type of WBC. The extra neutrophils may cause spleen and liver enlargement and may quickly progress to acute leukemia.

This type of leukemia is rare.

Chronic eosinophilic leukemia

Chronic eosinophilic leukemia occurs when too many eosinophils (another type of WBCs) are present in the bone marrow, the blood, and other tissues. This condition can also quickly progress to acute leukemia.

This is also a rare condition.

Histiocytosis is a group of conditions that result from an overproduction of a type of WBCs known as histiocytes, which play a role in immune function.

In all forms of histiocytosis, these cells begin to attack the body, targeting structures such as the:

In 2016, the Histiocyte Society suggested arranging the forms of histiocytosis into five main groups depending on how the condition begins, presents, and progresses. These groups are:

  • L group, or Langerhans-related, such as Langerhans cell histiocytosis and Erdheim-Chester disease
  • C group, or cutaneous and mucocutaneous histiocytoses, such as juvenile xanthogranuloma
  • R group, or Rosai-Dorfman disease
  • M group, or malignant histiocytoses, such as histiocytic sarcoma and Langerhans cell sarcoma
  • H group, or hemophagocytic lymphohistiocytosis and macrophage activation syndrome

PNH is a condition that causes RBCs to break apart prematurely. Evidence suggests that PNH is a rare disorder, affecting 1–5 of every million people.

PNH typically occurs when variations of the PIGA or PIGT gene occur in blood-forming cells known as hematopoietic stem cells. These cells are abundant in the bone marrow and produce various types of blood cells. Changes in the PIGA or PIGT gene cause these blood cells to lack a protein that protects them from the body’s immune system.

The name comes from the fact that many people may notice sudden, irregular episodes of passing red or dark urine, especially at night or in the early morning. However, not everyone with PNH will have visibly dark urine.

People with PNH may experience frequent infections, anemia, and problems with blood clotting. However, the symptoms can vary greatly from person to person. Some people may experience only mild symptoms, while others may have serious symptoms that can progress to cause life threatening complications.

Castleman disease is a rare group of lymphoproliferative disorders involving enlargement of lymph node tissue. Evidence suggests that 4,300–5,200 people in the United States receive a diagnosis each year.

There are two main types of Castleman disease: unicentric (UCD) and multicentric (MCD). UCD is the more common type and affects lymph nodes in one area of the body. MCD is rarer and presents as enlarged lymph nodes throughout the body. MCD is typically more severe.

Health experts do not know the exact cause of Castleman disease, but it may result from problems with immune system regulation and certain infections. Signs and symptoms are more common with MCD and may include low RBC counts and irregular platelet levels.

Gaucher disease is a rare metabolic disorder that occurs in roughly 1 in 50,000–100,000 people.

Gaucher disease occurs when a person inherits a variation in the GBA gene. This gene provides the instructions for the enzyme glucocerebrosidase, which breaks down a sugary fat known as glucocerebroside.

Without this enzyme, cells cannot break down glucocerebroside, and it builds up, preventing the cells from functioning correctly. Enlarged cells containing glucocerebroside are known as Gaucher cells.

Gaucher cells may build up in the spleen, liver, or bone marrow. When this happens, the tissue or organ may enlarge and stop functioning correctly. When Gaucher cells damage the bone marrow, this can interfere with the production of RBCs and platelets. Deficiencies in these components of blood can lead to anemia and blood clotting problems.

Treatment depends on the blood disorder a person has, the blood cells it affects, and the symptoms a person experiences. In some cases, healthcare professionals cannot cure the condition but can help manage it.

Potential treatment options for myeloproliferative disorders include:

Possible treatments for lymphoproliferative disorders include:

  • stem cell transplants
  • immunosuppressants
  • chemotherapy
  • steroids
  • antiviral therapy

The following are some questions people frequently ask about rare blood disorders.

What are the most rare blood disorders?

There are many rare blood disorders, and it is difficult to measure which are the rarest. Polycythemia vera, histiocytosis, and PNH are some examples of rare blood disorders.

Which blood disorder is not treatable?

Typically, treatment is available for all blood disorders, but not every blood disorder is curable. For example, treatment is available to help effectively manage polycythemia vera for long periods, but no cure is currently available.

What is a rare red blood cell disease?

Blood disorders can affect different components of the blood, such as RBCs. Diamond-Blackfan anemia is one rare blood disease that affects RBCs.

Learn more about red blood cell disorders.

Rare blood disorders are uncommon conditions that affect the blood cells’ ability to function correctly. Health experts may categorize them as myeloproliferative or lymphoproliferative depending on the types of blood cells they affect.

Common symptoms may include anemia and problems with blood clotting. Treatment will depend on the condition but may include chemotherapy and stem cell transplants.