Who is Shiva Stone from Cutting for Stone and what is their importance?

Shiva Stone is Marion's twin brother. They were conjoined by the head at birth. Shiva later learns that his skull plates had overlapped with his twin's, giving him an extra-strong forehead. Throughout his childhood, he struggled with a variety of medical issues, such as sleep apnea and muteness. Shiva is described as a shy, contemplative child, who seems only concerned with himself and his own success in life.