Clinical Laboratory Methods: Atlas of Commonly Performed Tests by Michael Laposata and Peter McCaffrey

Author:Michael Laposata and Peter McCaffrey
Language: eng
Format: epub
Publisher: McGraw Hill
Published: 2022-05-15T00:00:00+00:00

DETECTION OF A GENOMIC ALTERATION USING CGH

This figure shows how CGH can be used to identify a genomic alteration in a patient sample. The example shown is from a patient with a partial deletion of a chromosome who carries a diagnosis of Cri du Chat syndrome with a partial deletion of the short arm of chromosome 5. The principle of the test requires separately fragmenting normal DNA and patient (sample) DNA, and comparing results using each set of fragments. Separately colored fluorescent tags are added, and these tagged DNA fragments compete for binding to a collection of chromosomes in a metaphase spread.

In the figure, normal DNA labeled with a green fluorophore and sample DNA labeled with a red fluorophore have been fragmented, and each of these is added to the collection of chromosomes in a metaphase spread. If both the normal and sample DNA contain equal amounts of a specific chromosomal region, then their fragments will bind in equal amounts to that corresponding section of the metaphase chromosomes. The combination of the two fluorophores will result in a yellow color. Conversely, if the sample DNA is missing a chromosomal region, such as having a deletion in the short arm of chromosome 5, then only the normal DNA will bind to that chromosomal region, resulting in that region appearing green.

For higher resolution, the balance of fluorescence from red to yellow to green can be quantitated using a fluorescence detector and whole metaphase chromosomes may be replaced with arrays of specific chromosomal segments spread over a plate. This method, commonly referred to as array CGH, is depicted in the previous figure.

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