PHILIPPA RUSSELL’S son, Simon, has spent his life defying the odds. Born with fluid on the brain, he was one of the first children to have successful life-saving shunt surgery. He surprised his doctors first by making it out of his teens, then again by living to 35. Today he is 60, and the expectation is that he could live into his 80s. That prospect should fill her with joy. Instead she is frantic with worry.