Copy-number Variation - Role in Disease

Role in Disease

Like other types of genetic variation, some CNVs have been associated with susceptibility or resistance to disease. Gene copy number can be elevated in cancer cells. For instance, the EGFR copy number can be higher than normal in non-small cell lung cancer. In addition, a higher copy number of CCL3L1 has been associated with lower susceptibility to HIV infection, and a low copy number of FCGR3B (the CD16 cell surface immunoglobulin receptor) can increase susceptibility to systemic lupus erythematosus and similar inflammatory autoimmune disorders. Copy number variation has also been associated with autism, schizophrenia, and idiopathic learning disability.

However, although once touted as the explanation for the elusive hereditary causes of complex diseases like rheumatoid arthritis, the most common CNVs have little or no role in causing disease.

Among common functional CNVs, gene gains outnumber losses, suggesting that many of them are favored in evolution and, therefore, beneficial in some way. One example of CNV is the human salivary amylase gene (AMY1). This gene is typically present as two diploid copies in chimpanzees. Humans average over 6 copies and may have as many as 15. This is thought to be an adaptation to a high-starch diet that improves the ability to digest starchy foods.