Tuvan Syndrome is a neurological condition that affects Vulcanoid species such as Vulcans, Romulans and Rigelians. It is degenerative and uncurable as of 2375. In the United Federation of Planets, several studies on Vulcans who were affected by the disease were undertaken. Early symptoms of Tuvan Syndrome include displaced weakness of facial muscles, irregular and displaced eyelids. The disease can be accelerated by exposure to nadion radiation.
Praetor of the Romulan Star Empire D'deridex was known to had suffered from the illness during the later stages of his life in the mid-22nd century. In 2155, during the Earth-Romulan War, he was known to had made irrational decisions leading to a number of setbacks in the war against the Coalition of Planets. Admiral Valdore was even to had noted that the actions of the D'deridex seemed to be insane to him. (ENT novel: Beneath the Raptor's Wing)
- In Catalyst of Sorrows, the disease is referred to as "Tuvan's Syndrome", suggesting Tuvan was the first individual to suffer from it, or was the person who first diagnosed it.