Philadelphia chromosome (Ph)
BCR-ABL on the Ph chromosome and ABL-BCR on the chromosome 9 participating in the translocation. The BCR-ABL gene encodes a protein with deregulated (uncontrolled) tyrosine kinase activity. The presence of this protein in the CML cells is strong evidence of its pathogenetic (disease-causing) role. The efficacy in CML of a drug that inhibits the BCR-ABL tyrosine kinase has provided the final proof that the BCR-ABL oncoprotein is the unique cause of CML.
The Ph chromosome is also found in a form of acute lymphoblastic leukemia (ALL). It seems highly probable that this form of ALL is due to the same chromosomal and molecular mechanisms as CML.
Philadelphia chromosome The hallmark of chronic myeloid leukemia (CML). The Philadelphia (Ph) chromosome is an abbreviated chromosome 22 that was shortchanged in an a reciprocal exchange of material with chromosome 9. This translocation occurs in a cell in the bone-marrow cell, and causes CML It is also found in a form of acute lymphoblastic leukemia (ALL). On a molecular level the Philadelphia chromosome translocation results in the production of a fusion protein. A large portion of a proto-oncogene, called ABL, on chromosome 9 is translocated to the BCR gene on chromosome 22. The two gene segments are fused and ultimately produce a chimeric protein that is larger than the normal ABL protein. The malignant state is a consequence of this process. Understanding this process led to the development of the drug imatinib mesylate (Gleevec) the first in a new class of genetically targeted agents, a major advance in cancer treatment..
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