Chapter

Robertsonian Translocations

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/9780195375336.003.0007

Series: Oxford Monographs on Medical Genetics

Robertsonian Translocations

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THE AMERICAN INSECT CYTOGENETICIST W. R. B. Robertson first described translocations of chromosomes resulting from the fusion of two acrocentrics in his study of insect speciation in 1916, and this type of translocation is named Robertsonian (abbreviation rob) in his honor. There are five human acrocentric autosomes—chromosomes 13, 14, 15, 21, and 22 (the 13, 14, and 15 are the D group chromosomes, and the 21 and 22 comprise the G group)—and all are capable of participating in this type of translocation. The composite chromosome produced includes the complete long arm chromatin of the two fusing chromosomes, although it lacks at least some of the short arm chromatin. Robertsonian translocations are among the most common balanced structural rearrangements seen in the general population with a frequency in newborn surveys of about 1 in 1000 (Blouin et al., 1994). Historically, the most important Robertsonian translocations are the D;21 and G;21, which are the basis of most familial translocation Down syndrome. Uniparental disomy is of relevance, with respect to the two imprintable acrocentrics, chromosomes 14 and 15.

In this chapter, we consider the case of the phenotypically normal person who carries, in balanced form, a Robertsonian translocation. We generally use a short cytogenetic description for the carrier state, thus, 45,XX,rob(14q21q) or simply rob(14q21q). The formally correct ICSN designation for a short arm to short arm fusion Robertsonian translocation is, for example, 45,XX,der(14;21)(q10;q10) or 45,XX,rob(14;21)(q10;q10).

Chapter.  7385 words.  Illustrated.

Subjects: Clinical Genetics

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