Illustration by Nahal Sheikh Before I walked into Ruby’s room, I always paused at the door and put on a smile. It became a ritual. However bad the day had been, however frightened or tired I was, I would stop for a second, breathe, and walk in smiling. Then I would start singing her little Ruby song. For a long time she could not really track me, but her eyesight improved, and eventually she followed me all the way from the door to her bed. In a life that had become full of numbers, risks, alarms and waiting, there she was, watching her dad come into the room. For two and a half years of her life, my wife Elle and I lived between home and Great Ormond Street Hospital. Our daughter Ruby had an ultra-rare condition called PMM2-CDG, which disrupts how the brain, liver, heart, and hormones develop and function.…