Chronic Myelogenous Leukemia

Philadelphia Chromosome

An abnormal arrangement of several of the chromosomes that contain protein-producing genes has been found in leukemic cells of the bone marrow and blood. This discovery occurred many years ago when a researcher found that a portion of chromosome 9 can exchange material with chromosomes 22. This causes a gene known as "abl" to become located next to the "bcr" gene on chromosome 22. This abnormal gene — known as bcr-abl — produces an abnormal protein known as a tyrosine kinase that causes excessive production of white blood cells. The abnormal chromosome 22 containing the bcr-abl was first discovered in Philadelphia in 1961 and is known as the Philadelphia chromosome.