Taggart's Syndrome was a neurological disorder which afflicted Humans. The disorder was known to usually cause death by the age of twenty. The only known treatment was Rigelian gene therapy.
John Frederick Paxton, leader of the xenophobic group Terra Prime, suffered from this condition, and took regular injections to treat himself. Commander T'Pol later noted Paxton's hypocrisy for using an alien medical treatment, which conflicted with his beliefs of Human purity. (ENT: "Terra Prime")
The name is most likely a reference to Chuck Taggart, a character from the short-lived series Odyssey 5, who was played by Peter Weller, who also played John Paxton. Odyssey 5 was also created by Enterprise Executive Producer Manny Coto.