Acute promyelocytic leukemia is a form of acute myeloid leukemia, a cancer of the blood-forming tissue (bone marrow). In normal bone marrow, hematopoietic stem cells produce red blood cells (erythrocytes) that carry oxygen, white blood cells (leukocytes) that protect the body from infection, and platelets (thrombocytes) that are involved in blood clotting. In acute promyelocytic leukemia, immature white blood cells called promyelocytes accumulate in the bone marrow. The overgrowth of promyelocytes leads to a shortage of normal white and red blood cells and platelets in the body, which causes many of the signs and symptoms of the condition.

People with acute promyelocytic leukemia are especially susceptible to developing bruises, small red dots under the skin (petechiae), nosebleeds, bleeding from the gums, blood in the urine (hematuria), or excessive menstrual bleeding. The abnormal bleeding and bruising occur in part because of the low number of platelets in the blood (thrombocytopenia) and also because the cancerous cells release substances that cause excessive bleeding.

The low number of red blood cells (anemia) can cause people with acute promyelocytic leukemia to have pale skin (pallor) or excessive tiredness (fatigue). In addition, affected individuals may heal slowly from injuries or have frequent infections due to the loss of normal white blood cells that fight infection. Furthermore, the leukemic cells can spread to the bones and joints, which may cause pain in those areas. Other general signs and symptoms may occur as well, such as fever, loss of appetite, and weight loss.

Acute promyelocytic leukemia is most often diagnosed around age 40, although it can be diagnosed at any age.

Normal Function

The PML gene provides instructions for a protein that acts as a tumor suppressor, which means it prevents cells from growing and dividing too rapidly or in an uncontrolled way. The PML protein is found in distinct structures in the nucleus of a cell called PML nuclear bodies (PML-NBs). In the PML-NBs, the PML protein interacts with other proteins that are involved in cell growth and division (proliferation) and self-destruction (apoptosis). The PML protein is able to block cell proliferation and induce apoptosis in combination with other proteins. Researchers believe that the structure of the PML-NBs is required for blocking proliferation and inducing apoptosis.

Health Conditions Related to Genetic Changes

Acute promyelocytic leukemia

Gene mutations can be acquired during a person's lifetime and are present only in certain cells. These mutations are called somatic mutations, and they are not inherited. A somatic mutation involving the PML gene causes acute promyelocytic leukemia, a cancer of the blood forming tissue (bone marrow). Acute promyelocytic leukemia is characterized by an accumulation of immature white blood cells, called promyelocytes, in the bone marrow. A rearrangement (translocation) of genetic material between chromosomes 15 and 17, written as t(15;17), fuses part of the PML gene on chromosome 15 with part of another gene on chromosome 17 called RARA. The protein produced from this fused gene, PML-RARα, functions differently than the protein products of the normal PML and RARA genes.

The PML-RARα protein does not localize to the PML-NBs, and the structures do not form properly. The PML-RARα protein is unable to block cell proliferation or induce apoptosis.

Additionally, the function of the RARα protein, the product of the RARA gene, is disrupted. Normally, this protein is involved in the regulation of gene transcription, which is the first step in protein production. Specifically, this protein helps control the transcription of certain genes important in the maturation (differentiation) of white blood cells beyond the promyelocyte stage. However, the PML-RARα protein blocks (represses) gene transcription.

The PML-RARα protein allows abnormal cell proliferation and blocks the differentiation of white blood cells at the promyelocyte stage. As a result, excess promyelocytes accumulate in the bone marrow and normal white blood cells cannot form, leading to acute promyelocytic leukemia.

Other Names for This Gene

• MYL
• promyelocytic leukemia protein
• promyelocytic leukemia, inducer of
• RING finger protein 71
• RNF71
• TRIM19
• tripartite motif protein TRIM19

Genomic Location

Normal Function

The RARA gene provides instructions for making a transcription factor called the retinoic acid receptor, alpha (RARα). A transcription factor is a protein that attaches (binds) to specific regions of DNA and helps control the activity of particular genes. The RARα protein controls the activity (transcription) of genes that are important for the maturation (differentiation) of immature white blood cells beyond a particular stage called the promyelocyte.

The RARα protein binds to specific regions of DNA and attracts other proteins that help block (repress) gene transcription, the first step in protein production. In response to a specific signal, the repressive proteins are removed and other proteins that induce gene transcription bind to the RARα protein, allowing gene transcription and cell differentiation.

Health Conditions Related to Genetic Changes

Acute promyelocytic leukemia

Gene mutations can be acquired during a person's lifetime and are present only in certain cells. These mutations are called somatic mutations, and they are not inherited. A somatic mutation involving the RARA gene causes acute promyelocytic leukemia, a cancer of the blood forming tissue (bone marrow). Acute promyelocytic leukemia is characterized by an accumulation of promyelocytes in the bone marrow. A rearrangement (translocation) of genetic material between chromosomes 15 and 17, written as t(15;17), fuses part of the RARA gene on chromosome 17 with part of another gene on chromosome 15 called PML. The protein produced from this fused gene, the PML-RARα protein, functions differently than the protein products of the normal PML and RARA genes.

The PML-RARα protein binds to DNA and represses gene transcription, like the normal RARα protein. However, the PML-RARα protein does not respond to the signal to induce transcription of genes, so the genes remain repressed.

Additionally, the function of the PML protein, the product of the PML gene, is disrupted. The PML protein blocks cell growth and division (proliferation) and induces self-destruction (apoptosis) in combination with other proteins. However, the PML-RARα protein does not block proliferation or induce apoptosis.

The PML-RARα protein blocks the differentiation of blood cells at the promyelocyte stage and allows abnormal cell proliferation. As a result, excess promyelocytes accumulate in the bone marrow and normal white blood cells cannot form, leading to acute promyelocytic leukemia.

Other Names for This Gene

• NR1B1
• nuclear receptor subfamily 1 group B member 1
• RAR
• RAR-alpha
• retinoic acid receptor, alpha

Genomic Location

Most cases of APL are treated with an anthracycline chemotherapy drug (daunorubicin or idarubicin) plus the non-chemotherapy drug, all-trans-retinoic acid (ATRA), which is a relative of vitamin A. This treatment leads to remission in 80% to 90% of patients.

Patients who cannot tolerate an anthracycline drug may get ATRA plus another drug called arsenic trioxide. Arsenic trioxide has also proven to be an effective alternative for the 20% to 30% of patients with APL who don't respond to initial treatment or who relapse. If treatment with arsenic trioxide achieves a remission, further courses of this drug may be given. A stem cell transplant may also be an option. If a second remission is not achieved, treatment options may include a stem cell transplant or taking part in a clinical trial.

Acute promyelocytic leukemia accounts for about 10 percent of acute myeloid leukemia cases. Acute promyelocytic leukemia occurs in approximately 1 in 250,000 people in the United States.