Philadelphia chromosome

Philadelphia chromosome Abbreviated Ph, the hallmark of chronic myeloid leukemia (CML), a small chromosome 22 that was shortened in a reciprocal exchange of material with chromosome 9. This translocation occurs in a cell in the bone marrow 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. Understanding this process led to the development of the drug imatinib mesylate (brand name: Gleevec), the first in a new class of genetically targeted agents against leukemia.