Comparitive genomic hybridization (CGH) or
Chromosomal microarray analysis(CMA) is a modern cytogenetic technique for analyzing variations in DNA copy-number. Alteration in DNA copy number is one of the many ways in which modification of gene expression and function occurs. The technology was initially used for studying chromosomal imbalances in solid tumours.
Large-scale copy number variations in the human genome leading to chromosomal imbalances comprise approximately 12% of the entire genome and some 10% of all known genes.A copy number variation (CNV)is defined as a DNA segment of longer than 1 kb with a variable copy number compared with a normal reference genome. Copy number variations are bounded by a stretch of similar DNA sequences called low-copy repeats or segmental duplications (or interspersed duplication blocks) which may potentially act as recombination hot spots.It should be noted that variations in DNA copy number though associated with disease states, can also be seen in healthy individuals
In recent years chromosomal microarray analysis have come into routine use in child neurology to enable genome-wide evaluation in developmental delay, mental retardation, and autistic spectrum disorders. Chromosomal microarray results should be interpreted with care with the help of published genetic databases,because of the relatively large number of benign CNV in normal individuals. Early consultation should be made with a clinical geneticist.
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