Stem Cell Transplant for Inborn Errors of Metabolism

Prior to transplantation, subjects will receive Busulfan intravenously (IV) via the Hickman line four times daily for 4 days, Cyclophosphamide intravenously via the Hickman line once a day for 4 days, and Anti-Thymocyte Globulin (ATG) intravenously (IV) via the Hickman line twice daily for three days before the transplant. These three drugs are being given to subjects to help the new marrow "take" and grow. On the day of transplantation, the donor's hematopoietic cells will be transfused via central venous catheter. After hematopoietic cell transplant, subjects will then receive two drugs, cyclosporin and either methylprednisolone or Mycophenolate Mofetil (MMF). Cyclosporin and methylprednisolone or MMF are given to help prevent the complication of graft-versus-host disease and to decrease the chance that the new donor cells will be rejected.