FULL TITLE: How a one-in-400million disability became common in a tiny polygamist Mormon town after generations of inbreeding A polygamist Mormon enclave on the Arizona-Utah border is seeing more and more children being born with an extremely rare disorder that causes severe mental and physical retardation. Dr. Theodore Tarby, who specialized in rare childhood diseases, first discovered the problem in 1990, when a woman in the community brought her 10-year-old son to him. The boy had unusual facial features, such as a prominent forehead, low-set ears, widely-spaced eyes and a small jaw. He was also severely physically and mentally disabled....