Editing Mutation (section)

== Disease causation ==
Changes in DNA caused by mutation in a coding region of DNA can cause errors in protein sequence that may result in partially or completely non-functional proteins. Each cell, in order to function correctly, depends on thousands of proteins to function in the right places at the right times. When a mutation alters a protein that plays a critical role in the body, a medical condition can result. One study on the comparison of genes between different species of ''Drosophila'' suggests that if a mutation does change a protein, the mutation will most likely be harmful, with an estimated 70 per cent of amino acid polymorphisms having damaging effects, and the remainder being either neutral or weakly beneficial.<ref name="Sawyer2007" /> Some mutations alter a gene's DNA base sequence but do not change the protein made by the gene.  Studies have shown that only 7% of point mutations in noncoding DNA of yeast are deleterious and 12% in coding DNA are deleterious. The rest of the mutations are either neutral or slightly beneficial.<ref>{{cite journal | vauthors = Doniger SW, Kim HS, Swain D, Corcuera D, Williams M, Yang SP, Fay JC | title = A catalog of neutral and deleterious polymorphism in yeast | journal = PLOS Genetics | volume = 4 | issue = 8 | pages = e1000183 | date = August 2008 | pmid = 18769710 | pmc = 2515631 | doi = 10.1371/journal.pgen.1000183 | veditors = Pritchard JK | editor-link = Jonathan K. Pritchard | doi-access = free }}</ref>

=== Inherited disorders ===
{{See also|Genetic disorder}}
If a mutation is present in a [[germ cell]], it can give rise to offspring that carries the mutation in all of its cells. This is the case in hereditary diseases. In particular, if there is a mutation in a DNA repair gene within a germ cell, humans carrying such germline mutations may have an increased risk of cancer. A list of 34 such germline mutations is given in the article [[DNA repair-deficiency disorder]]. An example of one is [[albinism]], a mutation that occurs in the ''[[Oculocutaneous albinism type I|OCA1]]'' or ''[[OCA2]]'' gene. Individuals with this disorder are more prone to many types of cancers, other disorders and have impaired vision.

DNA damage can cause an error when the DNA is replicated, and this error of replication can cause a gene mutation that, in turn, could cause a genetic disorder. DNA damages are repaired by the DNA repair system of the cell. Each cell has a number of pathways through which enzymes recognize and repair damages in DNA. Because DNA can be damaged in many ways, the process of DNA repair is an important way in which the body protects itself from disease. Once DNA damage has given rise to a mutation, the mutation cannot be repaired.

=== Role in carcinogenesis ===
{{See also|Carcinogenesis}}
On the other hand, a mutation may occur in a somatic cell of an organism. Such mutations will be present in all descendants of this cell within the same organism. The accumulation of certain mutations over generations of somatic cells is part of cause of [[malignant transformation]], from normal cell to cancer cell.<ref>{{cite journal|vauthors=Ionov Y, Peinado MA, Malkhosyan S, Shibata D, Perucho M|s2cid=4254940|date=June 1993|title=Ubiquitous somatic mutations in simple repeated sequences reveal a new mechanism for colonic carcinogenesis|journal=Nature|volume=363|issue=6429|pages=558–61|bibcode=1993Natur.363..558I|doi=10.1038/363558a0|pmid=8505985}}</ref>

Cells with heterozygous loss-of-function mutations (one good copy of gene and one mutated copy) may function normally with the unmutated copy until the good copy has been spontaneously somatically mutated. This kind of mutation happens often in living organisms, but it is difficult to measure the rate. Measuring this rate is important in predicting the rate at which people may develop cancer.<ref>{{cite journal | vauthors = Araten DJ, Golde DW, Zhang RH, Thaler HT, Gargiulo L, Notaro R, Luzzatto L | title = A quantitative measurement of the human somatic mutation rate | journal = Cancer Research | volume = 65 | issue = 18 | pages = 8111–7 | date = September 2005 | pmid = 16166284 | doi = 10.1158/0008-5472.CAN-04-1198 | doi-access = free }}</ref>

Point mutations may arise from spontaneous mutations that occur during DNA replication. The rate of mutation may be increased by mutagens. Mutagens can be physical, such as radiation from [[ultraviolet light|UV rays]], [[X-ray]]s or extreme heat, or chemical (molecules that misplace base pairs or disrupt the helical shape of DNA). Mutagens associated with cancers are often studied to learn about cancer and its prevention.