Causes of APL: The role of DNA
During the past few years, scientists have made great progress in understanding how certain changes
in DNA can cause normal bone marrow cells to become leukemic cells. DNA is the chemical that
carries the instructions for nearly everything our cells do. Some genes (parts of our DNA) contain
instructions for controlling when our cells grow and divide. Certain genes that promote cell
division are called protooncogenes. Others that slow down cell division or cause cells to die at
the appropriate time are called tumor suppressor genes. We know that cancers can be caused by DNA
mutations (gene defects) that turn on protooncogenes or turn off tumor suppressor genes.
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Every time a cell prepares to divide into two new cells, it must duplicate its DNA. This process
is not perfect and copying errors can occur. Fortunately, cells have repair enzymes that
proofread DNA. But some errors may slip past, especially if the cells are growing rapidly.
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Translocations
Translocations are the best known type of DNA abnormality that can cause leukemia to develop.
Human DNA is packaged in 23 pairs of chromosomes. A translocation means that DNA from one
chromosome breaks off and becomes attached to a different chromosome.
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In translocation, a piece of one chromosome breaks off and trades places with the piece of another chromosome.
In acute promyelocytic leukemia (APL), the translocation occurs between genes that would normally
help to restrict tumor growth and help white blood cells to mature in a healthy way.
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When these genes trade places, a mutant gene is formed.
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The mutant gene formed by the translocation prevents normal genes from doing their job.
This mutant gene makes it difficult for normal genes to do their job. Because of this, leukemia cells
may not age as they're supposed to, and can increase in number to an unhealthy degree.
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Click here to learn more about diagnosing and testing for genetic
abnormalities in APL patients.
1. American Cancer Society. Do We Know What Causes Acute Myeloid Leukemia (AML)? Available at:
http://www.cancer.org/. Accessed September 1, 2006.
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