ABC's Robin Roberts, host of Good Morning America, (left) talks with Mark Zuckerberg, the founder and CEO of Facebook, in late April about the social network's push to get users to enroll as organ donors. This week Roberts is expected to receive a bone marrow transplant to treat myelodysplastic syndrome. Rick Rowell, ABC/via AP hide caption

itoggle caption Rick Rowell, ABC/via AP

All in the family: Nino Giarratano (left), the head baseball coach at the University of San Francisco, joins hands with his father, Mickey Giarratano, after the transplant of a kidney from son to father at Porter Adventist Hospital in Denver last year. AP/Courtesy Giarratano Family hide caption

itoggle caption AP/Courtesy Giarratano Family