What illness did Spock have?

Good day, I'm curious about a particular aspect of the popular Star Trek franchise. Could you please elaborate on what illness was depicted in the character of Mr. Spock? Was it a fictional condition created specifically for the show, or was it based on a real-life medical diagnosis? Furthermore, how did this illness affect his character development and the overall narrative of the series? I'd be grateful for any insights you might have on this intriguing topic.