Leukemia Chronic Myelogenous Philadelphia Chromosome

Chronic myelogenous leukemia can, in most cases, be traced to a genetic abnormality known as the Philadelphia chromosome. The Philadelphia chromosome triggers the release of a protein that leads to the rapid formation of leukemia cells. Imatinib, a targeted cancer medication, works by blocking proteins released by chronic myelogenous leukemia cells.

Chromosomes and DNA

Chromosomes are molecules of DNA found in cells. Most people have 23 pairs of chromosomes. Chromosomes contain all the genetic material needed to create, maintain and control the human body.

Cells reproduce by dividing into two new cells, each containing a copy of the original cell’s chromosomal information. During cell division, errors can occur and chromosomes can be altered.

The Philadelphia Chromosome

The Philadelphia chromosome is an example of an error that occurs during cell division. During replication, a section of chromosome 22 switches places with a section of chromosome 9. Such a process is called translocation. The result is a copy of chromosome 22 containing elements of chromosome 9, and vice versa.

The abnormal copy of chromosome 22 produced by this error is known as the Philadelphia chromosome. The Philadelphia chromosome produces a new gene called the BCR-ABL gene, which contains elements of chromosome 22 and chromosome 9.

CML and the BCR-ABL Gene

The BCR-ABL gene is an oncogene, a type of gene that triggers cell growth and cell division. The BCR-ABL gene occurs in white blood cells containing the Philadelphia chromosome.

The BCR-ABL gene causes the white blood cell to release tyrosine kinase, which causes the rapid growth and reproduction of abnormal white blood cells. Each of these blood cells contains the Philadelphia chromosome, eventually leading to the rapid accumulation of leukemia cells.

The Philadelphia Chromosome and CML

The Philadelphia chromosome occurs in 90 percent of chronic myelogenous leukemia cases, according to the Mayo Clinic (2008). In rare cases, chronic myelogenous leukemia results from the BCR-ABL gene without the Philadelphia chromosome, and some patients show no evidence of either the Philadelphia chromosome or the BCR-ABL gene. Such cases indicate that while the Philadelphia chromosome causes most cases of CML, other mechanisms can also cause chronic myelogenous leukemia.

The Philadelphia Chromosome and Heredity

Unlike many genetic conditions, the Philadelphia chromosome cannot be passed from parents to children. Chronic myelogenous leukemia is not hereditary.

Imatinib and the Philadelphia Chromosome

Imatinib is a first-line treatment for chronic myelogenous leukemia diagnosed in the disease’s initial, chronic phase. Imatinib is a targeted medication that blocks the action of tyrosine kinase, the protein produced by the BCR-ABL gene. By blocking the protein’s action, imatinib slows the production of leukemia cells. Imatinib is most effective when administered in the chronic phase of chronic myelogenous leukemia, and has greatly increased CML survival rates.

Resources

American Cancer Society. (2010). Leukemia — Chronic myeloid (myelogenous). Retrieved September 24, 2010, from http://www.cancer.org/Cancer/Leukemia-ChronicMyeloidCML/DetailedGuide/leukemia-chronic-myeloid-myelogenous-what-causes.

Mayo Clinic Staff. (2008). Chronic myelogenous leukemia. Retrieved September 24, 2010, from http://www.mayoclinic.com/health/chronic-myelogenous-leukemia/DS00564/DSECTION=causes.

Mayo Clinic Staff. (2010). Chronic myelogenous leukemia: Philadelphia chromosome. Retrieved September 24, 2010, from http://www.mayoclinic.org/chronic-myelogenous-leukemia/philadelphia.html.

National Bone Marrow Donor Program. (2010). Imatinib (gleevec®) treatment for CML. Retrieved September 24, 2010, from http://www.marrow.org/PATIENT/Undrstnd_Disease_Treat/Lrn_about_Disease/CML/Gleevec_Treatment_for_CML/index.html.

National Cancer Institute. (2009). General information about chronic myelogenous leukemia. Retrieved September 24, 2010, from http://www.cancer.gov/cancertopics/pdq/treatment/CML/patient/.