2012 Volume 15 Issue 1 Pages 105-113
The human chromosome consists of 22 autosome pairs and one pair of sex chromosomes. Chromosome preparations processed by G-banding reveal the characteristic banding pattern of each chromosome, and each chromosomal band is numbered by the International System for Human Cytogenetic Nomenclature (ISCN). Chromosome abnormalities in clude numerical (i.e. gain or loss of a whole chromosome) and structural (e.g. translocation, inversion, and deletion) abnormalities, and each abnormality is designated by symbols and abbreviated terms defined by the ISCN. A karyotype describes the total number of chromosomes, followed by sex chromosome constitution, and numerical/structural abnormalities of sex chromosomes and/or those of autosomes. Research into cytogenetic abnormalities in leukemia started with the discovery of the Philadelphia (Ph) chromosome in chronic myelocytic leukemia. J. D. Rowley in Chicago subsequently found that the Ph chromosome was generated by reciprocal chromosomal translocation between chromosomes 9 and 22 with the breakpoint on 9q34 and 22q11.2, respectively. The BCR-ABL fusion gene is generated on the Ph chromosome, thereby encoding the BCR-ABL chimeric oncoprotein. Many recurrent chromosome abnormalities have been identified in acute myelocytic leukemia, including t(8;21)(q22;q22), inv(16)(p13.1q22)/t(16;16)(p13.1;q22), t(15;17)(q22;q12), and t(9;11)(p22;q23), and leukemia-associated genes have been cloned on each breakpoint. On the other hand, -5/del(5q) and -7/del(7q) have been found in secondary leukemia and are associated with myelodysplastic morphology. Fluorescence in situ hybridization has been introduced into the laboratory to identify specific chromosomal translocations and deletions, and is applicable to not only metaphase spreads but also interphase nuclei. As chromosome abnormalities are closely associated with the morphology of leukemic cells and treatment outcomes of patients, cytogenetic analysis is one of the crucial tests for the diagnosis and treatment of leukemia.
