Down Syndrome, Other Full Aneuploidies, Polyploidy, and the Influence of Parental Age

Abstract

This chapter reviews the archetypical chromosome disorder, namely Down syndrome (DS; trisomy 21), and the various different chromosomal forms that may be the basis of it: standard trisomy 21, translocation trisomy, both de novo and inherited, and other rare forms. The concept of dosage imbalance as the basis of the pathogenesis is reviewed, and the “DS critical region” on chromosome 21 is examined. Reproductive risks associated with each of these DS types are discussed. The chapter considers the other full autosomal trisomies, T13 and T18, and also (mosaic) T9. Triploidy, as the basis of hydatidiform mole, is reviewed. Also reviewed are the influence of parental, mostly maternal, age, in the..