Chapter

Autosomal Reciprocal 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/9780195375336.003.0005

Series: Oxford Monographs on Medical Genetics

Autosomal Reciprocal Translocations

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RECIPROCAL TRANSLOCATIONS ARE COMMON, and every counselor can expect to see translocation families. The usual form is the simple, or two-way, reciprocal translocation: only two chromosomes, usually autosomes, are involved, with one breakpoint in each. It is this category we consider in this chapter. The special cases of translocations involving sex chromosomes, and of complex translocations, are dealt with in separate chapters.

The translocation heterozygote (carrier) may have a risk to have a child who would be mentally and physically abnormal due to a “segmental aneusomy.” Typically, the imbalance is due to a segment of one of the participating chromosomes being duplicated and a segment of the other chromosome being deleted. This confers a partial trisomy and a concomitant partial monosomy. A few translocations are associated with a high risk, as much as 20%, or very rarely up to 50%, to have an abnormal child. Many translocations imply an intermediate level of risk, in the region of 5%–10%. Some carriers have a low risk, 1% or less; but the woman who is a carrier, or the partner of a male carrier, may have a high miscarriage rate. Others imply, apparently, no risk to have an abnormal child, but the likelihood of miscarriage is high. Yet others, discovered fortuitously, seem to be of no reproductive significance, with carriers having no difficulties in conceiving or carrying pregnancies and having normal children. The counselor needs to distinguish these different functional categories of translocation, in order to provide each family with tailor-made advice.

Chapter.  22466 words.  Illustrated.

Subjects: Clinical Genetics

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