Even before her first birthday, Jashaia Trinity Small startled more easily than other children exposed to loud noises. Once an ambitious walker, she began to fall more often and needed support to stand up. She blinked repeatedly, "and when you called her, she had to look around the room to see where you were," her mother, Nadine Green-Small recalls."By the time she was a year and a half, I knew something was really not right," Green-Small said. Last fall, Jashaia Small was diagnosed with Tay-Sachs disease, a genetic disorder most often diagnosed in eastern European Jews and only rarely in...