Congenital Hematological Disorder

This study is being done to determine how long it takes for the engraftment (recovery of blood cell counts) of umbilical cord stem cells and also how often engraftment of umbilical cord stem cells transplanted from an unrelated donor fails. Another purpose will be to document the rate of disease-free survival and the rate of relapse (a return of your disease or syndrome) as well as the incidence and severity of graft versus host disease (GvHD) following cord blood stem cell transplantation. GvHD is a complication of stem cell transplants in which white blood cells from the transplanted tissue (graft) attack the transplant recipient's body (host).