Yes, GLYCOGENS is a Scrabble word!

Letter values in Scrabble US: G 2, L 1, Y 4, C 3, O 1, G 2, E 1, N 1, S 1.

Is it a valid word?

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

one form in which body fuel is stored; stored primarily in the liver and broken down into glucose when needed by the body

Also: animal starch.