Copy Number Variation (CNV)
Copy number variation (abbreviated CNV) refers to a circumstance in which the number of copies of a specific segment of DNA varies among different individuals’ genomes. The individual variants may be short or include thousands of bases. These structural differences may have come about through duplications, deletions or other changes and can affect long stretches of DNA. Such regions may or may not contain a gene(s).
Copy number variation is a type of structural variation where you have a stretch of DNA, which is duplicated in some people, and sometimes even triplicated or quadruplicated. And so when you look at that chromosomal region, you will see a variation in the number of copies in normal people. Sometimes those copy number variants include genes, maybe several genes, which may mean that this person has four copies of that gene instead of the usual two, and somebody else has three, and somebody else has five. Interesting, we didn't really expect to see so much of that. It's now turning out to be pretty common, and in some instances, if those genes are involved in functions that are sensitive to the dosage, you might then see a consequence in terms of a disease risk.