Chapter

Down Syndrome, Other Full Aneuploidies, and Polyploidy

R. J. McKinlay Gardner, Grant R. Sutherland and Lisa G. Shaffer

in Chromosome Abnormalities and Genetic Counseling

Fourth edition

Published on behalf of Oxford University Press

Published in print November 2011 | ISBN: 9780195375336
Published online October 2012 | e-ISBN: 9780199975174 | DOI: http://dx.doi.org/10.1093/med/9780195375336.003.0018

Series: Oxford Monographs on Medical Genetics

Down Syndrome, Other Full Aneuploidies, and Polyploidy

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IN THIS CHAPTER we consider the case of parents, themselves karyotypically normal, who have had a child, or a pregnancy that aborted, with a full aneuploidy or a polyploidy. Thus, we include the major trisomies (13, 18, 21) and sex chromosome aneuploidies (XXX, XXY, XYY, and 45,X) as well as less commonly seen autosomal aneuploidies and sex chromosome polysomies. The category of polyploidy is substantially devoted to triploidy. In the great majority, these defects arise from an abnormal event during meiosis or (in some triploidy) at conception. In a few, there is postzygotic generation of aneuploidy. Only in the case of parental gonadal mosaicism, or in the hypothetical setting of an apparent predisposition to meiotic error, will there apply an increased risk of recurrence of aneuploidy, over and above that associated with any parental age effect. Triploidy needs separate consideration.

Chapter.  9698 words.  Illustrated.

Subjects: Clinical Genetics

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