A man who agreed to donate part of his liver to help a sick relative died while undergoing the transplant procedure at Lahey Clinic in Burlington, MA, two weeks ago, the hospital said. It was only the third death of an adult living liver donor in the United States in the two decades since the first procedure was done, according to two leading transplant surgeons. A total of 4,036 have been performed. Specialists said the death of a living donor is especially upsetting because they are generally young and healthy and are undergoing an operation they do not need for the benefit of a family member or close friend, the Boston Globe reports.