Were there any actual in-story implication that Splinter may never have been normal?

[neatoman]

I know Peter Laird has said Splinter was not a normal rat before he mutated and it was even in that packet Mirage sent to Playmates. However, was there any story that actually explained this? And I don't mean just showing he was able to remember martial arts moves and a love triangle in detail, I mean do they ever outright say or directly imply he had natural mutations and/or psychic powers when he was still a seemingly normal rat?