Yes, MUTAGEN is a Scrabble word!

Letter values in Scrabble US: M 3, U 1, T 1, A 1, G 2, E 1, N 1.

Is it a valid word?

MUTAGEN is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

any agent (physical or environmental) that can induce a genetic mutation or can increase the rate of mutation