If memory serves, I don't think he was "actually" a musician, as he was basically doing "deep undercover journalism" to expose the recklessness and deep hedonism of a particular band. That adventure ended when, in a night of very confusing debauchery, he lost a hand to a mini, "prop" guillotine. That is the origin point for his general insanity.
And then, yeah, it's "step 2 ????" and he's a brilliant geneticist. For any other doctor villain, I would assume that meant he went back to school after the accident. But he is a Gerber baby, so it is entirely possible he got his advanced knowledge from, like, a radioactive textbook. It could happen!