The primary cause of Chronic Myelogenous Leukemia (CML) is a genetic abnormality called the Philadelphia chromosome.
The Philadelphia Chromosome: A Key Factor in CML
The Philadelphia chromosome is not an inherited condition; instead, it develops during a person's lifetime and is found within the cancer cells. It is a result of a genetic rearrangement between two specific chromosomes: chromosome 9 and chromosome 22.
How the Philadelphia Chromosome Forms
- Chromosome Breakage: The process begins with breaks occurring in both chromosome 9 and chromosome 22.
- Exchange of Parts: Following the breaks, a swap takes place where a piece of chromosome 9 switches places with a piece of chromosome 22.
- Shortened Chromosome 22: This exchange leads to a shortened chromosome 22, now known as the Philadelphia chromosome.
- New Instructions: This abnormal chromosome 22 carries new instructions for the cell which ultimately trigger the development of CML.
| Chromosome | Description | Role in CML |
|---|---|---|
| Chromosome 9 | A normal human chromosome | Part that swaps with Chromosome 22 in the formation of Philadelphia Chromosome |
| Chromosome 22 | A normal human chromosome | Part that swaps with Chromosome 9, resulting in the Philadelphia Chromosome |
| Philadelphia Chromosome | Abnormal, shortened chromosome 22 | Results in the new instructions that can lead to the development of CML |
Consequences of the Philadelphia Chromosome
The new gene formed by the fusion of parts of the two chromosomes on the Philadelphia chromosome produces a protein called BCR-ABL. This protein is a tyrosine kinase that signals the bone marrow to produce too many white blood cells. This overproduction of abnormal white blood cells is the hallmark of chronic myelogenous leukemia.
In summary, the Philadelphia chromosome, resulting from a breakage and exchange of genetic material between chromosomes 9 and 22, is the direct cause of the development of CML. The resulting genetic changes lead to the abnormal production of white blood cells.
