It also affected the endocrine and immune systems. It was caused by a disruption of neuroelectric impulses in the midbrain during mind melds performed by a Vulcan who has been improperly trained. It could be cured by a meld performed by an experienced melder.
The disease and its cure were known in Surak's time, but by the 22nd century the knowledge of the cure had been lost or suppressed. By the 22nd century, melding was considered an "unnatural" practice. As a result, those afflicted with Pa'nar Syndrome were ostracized from Vulcan society. Consequently, medical research towards finding a cure was not a priority. (ENT: "Kir'Shara")
Sub-Commander T'Pol contracted the disease in 2151 when Tolaris initiated a meld with her, although she did not discover this immediately. (ENT: "Fusion") Dr Phlox had managed to keep T'Pol's illness under control for over a year without informing Captain Archer of her condition. When Captain Archer found out about her illness he was upset that the knowledge was kept from him. But, his main concern was T'Pol's health and he subsequently defended T'Pol's rights. In 2152, Dr. Phlox was able to improve the course of treatment (with the help of Dr. Yuris, who was capable of mind melds but was not infected himself, as he provided T'Pol with all of the available medical research on the illness). (ENT: "Stigma") In 2154, T'Pol was cured by the Syrrannite leader T'Pau, who performed another mind meld on T'Pol to cure the illness. Consequently, T'Pau revealed that the disease was caused by Vulcans who were not properly trained in the practice of mind melds. (ENT: "Kir'Shara")