A second patient has been treated in a historic gene editing study in California, and no major side effects or safety issues have emerged from the first man's treatment nearly three months ago, doctors revealed Tuesday. Gene editing is a more precise way to do gene therapy, and aims to permanently change someone's DNA to try to cure a disease. In November, 44-year-old Brian Madeux became the first person to have gene editing inside the body for a metabolic disease called Hunter syndrome that's caused by a bad gene.