Clinical cytogenetics: Principles

Abstract

In this chapter, the principles of clinical cytogenetics are discussed. This includes an overview of the historical aspects of cytogenetics as well as methodology used for cytogenetic studies (e.g., fluorescence in situ hybridization), an examination of chromosome structure, and the myriad of reasons for cytogenetic studies. The clinical descriptions as well as the mechanism of formation of a number of chromosome abnormalities are examined including numerical abnormalities (aneuploidy and polyploidy) and structural abnormalities (deletions, ring chromosomes, isochromosomes, insertions, duplications, inversions, and reciprocal and Robertsonian translocations). Prevalence, mechanism of formation, and reproductive implications are discussed for each type of abnormalities. In particular, the group of contiguous gene syndromes is discussed in detail. These syndromes include (but are not limited to) Prader-Willi syndrome, Angelman syndrome, Miller-Dieker syndrome, velocardiofacial syndrome, Langer-Giedion syndrome, Aniridia-Wilms tumor association, Smith-Magenis syndrome, and Williams syndrome. More recent studies of microarray technology, to detect smaller aberrations and recurrent syndromes, are also discussed. Lastly, the clinical implications of a number of different sex chromosome abnormalities have been examined and discussed, allowing the information to examine the significance of the Lyon hypothesis and X-chromosome inactivation.