TY - CHAP M1 - Book, Section TI - Chromosome Disorders A1 - Spinner, Nancy B. A1 - Conlin, Laura K. A2 - Kasper, Dennis A2 - Fauci, Anthony A2 - Hauser, Stephen A2 - Longo, Dan A2 - Jameson, J. Larry A2 - Loscalzo, Joseph Y1 - 2014 N1 - T2 - Harrison's Principles of Internal Medicine, 19e AB - Alterations of the chromosomes (numerical and structural) occur in about 1% of the general population, in 8% of stillbirths, and in close to 50% of spontaneously aborted fetuses. The 3 × 109 base pairs that encode the human genome are packaged into 23 pairs of chromosomes, which consist of discrete portions of DNA, bound to several classes of regulatory proteins. Technical advances that led to the ability to analyze human chromosomes immediately translated into the revelation that human disorders can be caused by an abnormality of chromosome number. In 1959, the clinically recognizable disorder, Down syndrome, was demonstrated to result from having three copies of chromosome 21 (trisomy 21). Very soon thereafter, in 1960, a small, structurally abnormal chromosome was recognized in the cells of some patients with chronic myelogenous leukemia (CML), and this abnormal chromosome is now known as the Philadelphia chromosome. SN - PB - McGraw-Hill Education CY - New York, NY Y2 - 2021/04/19 UR - accessmedicine.mhmedical.com/content.aspx?aid=1120790670 ER -