Celerity-induced accelerated somatic mutation rate was a process of rapid genetic mutation, where an individual's body is changed in a manner paralleling millions of years of natural evolution, but occurring within a matter of hours.
Tom Paris of the USS Voyager experienced this condition after making a warp 10 flight, breaking the transwarp threshold, in 2372. His biochemistry began to change, causing an allergic reaction to water, the breakdown of electrolytes, and the congealing of interstitial fluids. The alveoli in his lungs mutated, resulting in him no longer processing oxygen but instead a nitrogen-acidichloride mixture. Eventually, his cellular membranes deteriorated and his lymphatic system collapsed, leading to his apparent death.
However, Paris awakened shortly after, apparently healthy. The Doctor found that his internal organs were being rearranged, some having been absorbed and others grown anew. There were also rapid transmutations in his nervous system, causing bouts of deranged behavior interspersed by moments of lucidity.
The Doctor believed that Paris' DNA could be forced to revert to its original state if the new genetic material was destroyed with antiprotons from Voyager's warp core. Before the treatment could be completed, Paris broke free of his isotropic restraint and abducted Captain Kathryn Janeway, escaping on another transwarp flight. The Voyager crew found them on an uninhabited planet, having transformed into amphibious creatures, as well as having produced offspring. The Doctor was then able to complete his antiproton treatment and restore them to normal. (VOY: "Threshold", "Vis à Vis")