Born a Gryffindor, Raised a Slytherin

Harry Potter was raised by a wealthy, neglectful and abusive family. He finds out that he was adopted and in fact a wizard after receiving an invitation to 'Hogwarts University' at the age of 18. What if the mark of the Dark Lord implanted a different, malevolent characteristic in the tormented Boy Who Lived? What if Harry was placed in Slytherin and befriended Draco Malfoy?