The side-effect of traveling at transwarp speeds. For unknown reasons, the human body undergoes a metamorphosis as a result of being subjected to transwarp travel.
Described as "genetic mutation" by the Intrepid-class starship's holographic doctor, the body progresses through an evolutionary process at highly accelerated speeds. Organs mutate to new forms or functions, vestigial organs disappear, and new organs are generated.
The syndrome also affects the emotional state of the victim, creating mood swings from normal lucidity to anger and paranoia. If the syndrome completely runs its course, the victim mutates completely into a salamander-like life-form.
In 2372 Lieutenant Paris of the U.S.S. Voyager was subjected to this syndrome after piloting a shuttlecraft in a transwarp drive test. Before he could be cured, he kidnapped Captain Janeway and triggered the same syndrome in her by taking her aboard a second transwarp shuttle flight. This was followed by the two mutated beings mating and producing offspring. Once returned to their starship, both were treated with antiproton radiation therapy, which successfully reversed the effects and return the Captain and ship's pilot to their human state.