Concept
A variant of uncertain (or unknown) significance (VUS) is a genetic variant that has been identified through genetic testing but whose significance to the function or health of an organism is not known. Two related terms are "gene of uncertain significance" (GUS), which refers to a gene that has been identified through genome sequencing but whose connection to a human disease has not been established, and "insignificant mutation", referring to a gene variant that has no impact on the health or function of an organism. The term "variant' is favored in clinical practice over "mutation" because it can be used to describe an allele more precisely (i.e. without inherently connoting pathogenicity). When the variant has no impact on health, it is called a "benign variant". When it is associated with a disease, it is called a "pathogenic variant". A "pharmacogenomic variant" has an effect only when an individual takes a particular drug and therefore is neither benign nor pathogenic. A VUS is most commonly encountered by people when they get the results of a lab test looking for a mutation in a particular gene. For example, many people know that mutations in the BRCA1 gene are involved in the development of breast cancer because of the publicity surrounding Angelina Jolie's preventative treatment. Few people are aware of the immense number of other genetic variants in and around BRCA1 and other genes that may predispose to hereditary breast and ovarian cancer. A recent study of the genes ATM, BRCA1, BRCA2, CDH1, CHEK2, PALB2 and TP53 found 15,311 DNA sequence variants in only 102 patients. Many of those 15,311 variants have no significant phenotypic effect. That is, a difference can be seen in the DNA sequence, but the differences have no effect on the growth or health of the person. Identifying variants that are significant or likely to be significant is a difficult task that may require expert human and in silico analysis, laboratory experiments and even information theory.
