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Chromosomal translocations, deletions, and inversions

Iris Schrijver, MD
James L Zehnder, MD
Athena M Cherry, PhD
Section Editor
Richard A Larson, MD
Deputy Editor
Jennifer S Tirnauer, MD


In this review, we will describe the most common structural chromosomal anomalies, give examples of disease processes resulting from these germline or somatic alterations, and discuss the mechanisms underlying these disorders. Due to the important role of chromosomal abnormalities in the pathogenesis of many hematological disorders, a general review of these specific aberrations is presented separately, as is a review of cytogenetic and molecular genetic tools used to characterize these abnormalities. (See "General aspects of cytogenetic analysis in hematologic malignancies" and "Tools for genetics and genomics: Cytogenetics and molecular genetics".)


Chromosomal aberrations are due to either numerical abnormalities or structural defects. The normal diploid number of chromosomes in humans is 46. There are 23 pairs of chromosomes with 22 pairs of autosomes and two sex chromosomes, the X and the Y. Human females have two X chromosomes (46,XX), while males have one X and one Y chromosome (46,XY).

Abnormality of chromosome number — A numerical abnormality in a cell's chromosomal endowment may be caused by the gain of one or more complete haploid chromosome sets (polyploid karyotype). An example is the triploid chromosomal number (eg, 69,XXY) in a partial hydatiform mole. (See "Gestational trophoblastic disease: Pathology", section on 'Genetics'.)

More commonly, there is a selective gain or loss of an individual chromosome (aneuploidy). As an example, trisomy 21, which causes Down syndrome, is characterized by the gain of one additional copy of chromosome 21. All mutations that change the total number of chromosomes are considered to be genome mutations.

Abnormality of chromosomal structure — Structural chromosomal anomalies, also called chromosomal mutations, comprise those changes that are due to one or more breaks in a chromosome. Following a break, the separated fragments are likely to participate in chromosomal rearrangements. Structural chromosomal changes can result in a displacement of chromosomal regions without any loss or duplication of genetic material (ie, balanced rearrangements) or they may be unbalanced:

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Literature review current through: Nov 2017. | This topic last updated: Oct 18, 2017.
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