somatic mutation
Meaning of somatic mutation: A DNA change acquired during life in one ordinary body cell, passed to its descendants but never to a child.
Definition of somatic mutation
A somatic mutation is a change in DNA that occurs after conception, in any cell of the body other than the egg or sperm cells. It is copied to every cell descended from the one where it arose, but it cannot be passed to a child. Somatic mutations accumulate throughout life, and most cause no harm, while a few drive the development of cancer.
How does it differ from an inherited change?
| Somatic mutation | Germline mutation | |
|---|---|---|
| When it arises | After conception | Present in the fertilized egg |
| Cells affected | One cell and its descendants | Every cell in the body |
| Passed to children | No | Yes, with a defined chance |
| Found in a blood sample | Usually not | Yes |
This distinction drives how testing is done. A tumor sample carries both kinds mixed together, so a germline mutation is confirmed by testing normal tissue such as blood or saliva alongside it.
Where do they come from?
Some are copying errors. Every time a cell divides it duplicates a vast amount of DNA, and proofreading is excellent but not perfect. Others are caused by damage: ultraviolet light in skin, chemicals in tobacco smoke in the lung and bladder, and the ordinary byproducts of using oxygen. Repair systems correct most of it. What escapes accumulates, which is why the number of somatic changes in a cell rises steadily with age and why age is the strongest single risk factor for most cancers.
Why do most cause no harm?
Position decides everything. The great majority of DNA does not code for a protein, so an alteration there usually changes nothing. A mutation inside a gene may still be silent, or may affect a gene that particular somatic cell does not use. Trouble arises when the change hits a gene controlling division or repair and gives that cell an advantage over its neighbors. It then outgrows them, its descendants acquire further changes, and cancer develops through several such steps rather than one. Patches of skin and blood in healthy older people are already made up of such expanded clones without any disease resulting.
Also known as
Used in a sentence
Sequencing identified a somatic mutation present in the tumor but absent from the blood sample.
Good to know
Tumor sequencing detects somatic and inherited changes together, so a result with implications for relatives is confirmed by testing normal tissue separately.
Word origin
Where “somatic mutation” comes from
Somatic comes from the Greek soma, meaning body; mutation from the Latin mutare, to change.