- The exact cause of CML is not known. However, genetic studies show that around 90% of CML patients have an abnormal chromosome called the ‘Philadelphia chromosome’.
- The Philadelphia chromosome contains a ‘fusion gene’ called BCR-ABL1. BCR-ABL1 is formed by the swap and fusion of chromosome 22’s BCR gene and chromosome 9’s ABL gene (Figure 2). BCR and ABL are abbreviations for the Breakpoint Cluster Region and Abelson genes, respectively.
Figure 2 Formation of the Philadelphia chromosome
Source: Leukaemia Care
- The Philadelphia chromosome is produced in the bone marrow by accident. No direct hereditary link has been shown for CML. This means that it cannot be inherited or passed onto the next generation. The BCR-ABL1 fusion gene produces an abnormal version of the tyrosine kinase enzyme which then allows overproduction of myeloid cells.
- Exposure to radiation, such as the nuclear explosions at Hiroshima, has been linked to a higher chance of developing CML.
- No firm association between CML and industrial chemicals or alkylating agents has been found.