Editing Mutation (section)

=== Nomenclature ===
In order to categorize a mutation as such, the "normal" sequence must be obtained from the DNA of a "normal" or "healthy" organism (as opposed to a "mutant" or "sick" one), it should be identified and reported; ideally, it should be made publicly available for a straightforward nucleotide-by-nucleotide comparison, and agreed upon by the scientific community or by a group of expert geneticists and [[biologist]]s, who have the responsibility of establishing the ''standard'' or so-called "consensus" sequence. This step requires a tremendous scientific effort. Once the consensus sequence is known, the mutations in a genome can be pinpointed, described, and classified. The committee of the Human Genome Variation Society (HGVS) has developed the standard human sequence variant nomenclature,<ref name="paper45">{{cite journal | vauthors = den Dunnen JT, Antonarakis SE | title = Mutation nomenclature extensions and suggestions to describe complex mutations: a discussion | journal = Human Mutation | volume = 15 | issue = 1 | pages = 7–12 | date = January 2000 | pmid = 10612815 | doi = 10.1002/(SICI)1098-1004(200001)15:1<7::AID-HUMU4>3.0.CO;2-N | s2cid = 84706224 | author-link2 = Stylianos Antonarakis | doi-access = free }}</ref> which should be used by researchers and [[Genetic testing|DNA diagnostic]] centers to generate unambiguous mutation descriptions. In principle, this nomenclature can also be used to describe mutations in other organisms. The nomenclature specifies the type of mutation and base or amino acid changes.
* Nucleotide substitution (e.g., 76A>T) – The number is the position of the nucleotide from the 5' end; the first letter represents the wild-type nucleotide, and the second letter represents the nucleotide that replaced the wild type. In the given example, the adenine at the 76th position was replaced by a thymine.
** If it becomes necessary to differentiate between mutations in [[genomic DNA]], [[mitochondrial DNA]], and [[RNA]], a simple convention is used. For example, if the 100th base of a nucleotide sequence mutated from G to C, then it would be written as g.100G>C if the mutation occurred in genomic DNA, m.100G>C if the mutation occurred in mitochondrial DNA, or r.100g>c if the mutation occurred in RNA. Note that, for mutations in RNA, the nucleotide code is written in lower case.
* Amino acid substitution (e.g., D111E) – The first letter is the one letter [[Amino acid#Table of standard amino acid abbreviations and properties|code]] of the wild-type amino acid, the number is the position of the amino acid from the [[N-terminus]], and the second letter is the one letter code of the amino acid present in the mutation. Nonsense mutations are represented with an X for the second amino acid (e.g. D111X).
* Amino acid deletion (e.g., ΔF508) – The Greek letter Δ ([[delta (letter)|delta]]) indicates a deletion. The letter refers to the amino acid present in the wild type and the number is the position from the N terminus of the amino acid were it to be present as in the wild type.