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The page below is a sample from the LabCE course Advances in Noninvasive Prenatal Testing For Down Syndrome and other Trisomies. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Testing Methods Used for CVS and Amniocentesis Samples, continued

Chromosomal microarray analysis (CMA)

CMA is a technique used to identify various types of abnormalities throughout the entire set of chromosomes. The technique provides comprehensive genetic testing for most of the common chromosomal disorders as well as a large number of severe genetic disorders not detected by routine chromosome analysis. CMA examines chromosomes in more detail to determine if gains or losses are present in DNA, which can lead to genetic conditions that cause significant disabilities.
CMA uses microarray technology that employs a grid covered with thousands of tiny probes consisting of small pieces of DNA from known locations on each of the 46 chromosomes. Unlike FISH, CMA permits high-resolution assessment of the entire genome. The technique identifies imbalances of chromosomal material between DNA from a control specimen compared to the fetus DNA. The technique detects genomic copy number variations (CNVs), which are chromosomal imbalances that result from the deletion and/or duplication of one or more sections of DNA. CMA can be used for prenatal identification of chromosome abnormalities.
CMA can be performed using two different laboratory techniques; array-comparative genomic hybridization (aCGH) and single nucleotide polymorphism oligonucleotide microarray analysis (SOMA). Although both techniques offer comparable detection of CNVs, SOMA is able to utilize the single nucleotide polymorphism (SNP) genotype information to detect triploidy and other chromosome abnormalities in multiple gestations as well as maternal cell contamination.
SNPs are a common type of genetic variation among individuals and represent a difference in a single DNA building block or nucleotide. Occurring normally throughout an individual's DNA, SNPs can act as biological markers to help locate genes that may be associated with disease. When SNPs occur within a gene or in a regulatory region near a gene, they may play a more direct role in disease by affecting the gene’s function.
As previously discussed, SOMA technology can be used as part of the CMA method to identify various SNPs occurring in the DNA of various genes. Typically, SOMA technology involves a micro-array containing immobilized, specific nucleotide probes which serve as targets for specific nucleic acid sequences labeled with florescent dyes. Hybridization occurs between complimentary nucleotide sequences in the probe and the patient DNA sample. A detection system identifies and records the fluorescent signal.