Elizabeth Parrish is 44, the tough-gunning, sharp-talking CEO of a life-sciences startup, and seemingly full of life herself. But she says she suffers from a deadly disease. Hoping to stave off the sickness, Parrish recently journeyed to a clinic in Colombia, where she underwent a course of therapy that the FDA hasn’t touched with a 10-foot pole. One treatment would alter her telomeres — the stuff at the end of her DNA. The other would inhibit a protein that stops muscle growth.