The Solitude of Prime Numbers by Paolo Giordano

Alice has walked with a limp since an emotionally damaging childhood skiing accident. Mattia is a mathematical genius whose guilt about the disappearance of his twin sister when they were both children has isolated him even further than his brilliance. They forge an unusual friendship in high school based on their mutual rejection by the rest of their classmates. Life puts them on different paths but, for both of them, isolation becomes a way of life. When their paths cross again, they must choose between a life that has become comfortable and a life they once imagined might be possible. Their story is a moving insight into lives defined by loneliness. I read this in one sitting hoping for a different ending.