TY - CHAP M1 - Book, Section TI - Chromosomal Aberrations A1 - Pyeritz, Reed E. A2 - Papadakis, Maxine A. A2 - McPhee, Stephen J. A2 - Rabow, Michael W. A2 - McQuaid, Kenneth R. PY - 2022 T2 - Current Medical Diagnosis & Treatment 2022 AB - Any deviation from the structure and number of chromosomes as displayed in eFigure 40–1 is, technically, a chromosomal aberration. Not all aberrations cause problems in the affected individual, but some that do not may lead to problems in offspring. About 1:200 live-born infants has a chromosomal aberration that is detected because of some effect on phenotype. This frequency increases markedly the earlier in fetal life the chromosomes are examined. By the end of the first trimester of gestation, most fetuses with abnormal numbers of chromosomes have been lost through spontaneous abortion. For example, Turner syndrome—due to the absence of one sex chromosome and the presence of a single X chromosome—is a relatively common condition, but it is estimated that only 2% of fetuses with this form of aneuploidy survive to term. Even more striking in live-born children is the complete absence of most autosomal trisomies and monosomies despite their frequent occurrence in young fetuses. SN - PB - McGraw-Hill Education CY - New York, NY Y2 - 2024/03/29 UR - accessmedicine.mhmedical.com/content.aspx?aid=1184181602 ER -