This term applies to a disease whose etiology is related to an alteration in DNA that occurs after conception. Somatic mutations occur in all body tissues throughout life and are not present in the germline from which the individual developed (The Greek word soma means body.) The majority of somatic mutations have no phenotypic effect. However, occasionally they may have functional consequences that confer a selective advantage on the cell owing to preferential growth or survival. These so-called driver mutations may ultimately lead to cancer or other diseases.