A rare medical condition, first posited by Nelson on the BBC TV puppet comedy Mongrels, which causes patients given twenty four hour care to live for years and years and years, despite having multiple diseases, ailments and genetic disorders that would otherwise fatal.
"Still, not being horrible or nothing but he probably won't last that long."
"That's the truly wonderful thing actually. He's got a condition called "Persistent Forsyth Syndrome". Given twenty-four hour care, he'll live for years and years and years. And years. And years. And years. Which is obviously *yawn* really great news."