The option of Transgendered doesn't need to be in the game for your character to be so. Your gender variance is totally up to you, in the same way your character's back story, decisions, and interactions are. Now, if you want certain Physical aspects from each gender I guess you're out of luck, but then there are many games where you can customize body proportions. Elder Scrolls, EVE online, and Dark Souls (Kinda) to name a few.