Chromosomal microarray (CMA) testing can be a powerful diagnostic tool when used appropriately. The CMA technology and testing process may differ from other lab tests you are accustomed to, but with attention to the steps outlined in this program, you can successfully apply this test in your practice. In this section we discuss the background knowledge you will need when deciding whether to order chromosomal microarray, including how the test works, what it detects, and when it has proven useful. Below are key questions you should understand before deciding to test with chromosomal microarray.

Chromosomal microarray (CMA) testing looks for extra (duplicated) or missing (deleted) chromosomal segments, sometimes called copy number variants (CNVs). These include 1. Microdeletions and microduplications of chromosome segments, which are too small to see under a microscope but may contain multiple genes (see illustration below). 2. Most abnormalities of chromosome number (trisomy, monosomy, etc.), including Down syndrome. 3. Most unbalanced rearrangements of chromosome structure (translocations, etc.).

Depending on the platform, CMA may also detect:

Excessive homozygosity, suggestive of risk for recessive disease or imprinting disorders (see Apply Results for more information)

Triploidy and other duplications of the entire chromosome set (tetraploidy, etc.)

As with traditional karyotype, mosaicism (a mixture of normal and abnormal cells) of greater than 20-25% can be detected by CMA testing. Detection rates vary with the specific testing platform ms).

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