Treosulfan and Fludarabine Phosphate Before Donor Stem Cell Transplant in Treating Patients With Nonmalignant Inherited Disorders

OUTLINE: CONDITIONING REGIMEN: Patients receive treosulfan intravenously (IV) over 2 hours on days -6 to -4 and fludarabine phosphate IV over 1 hour on days -6 to -2. Patients receive anti-thymocyte globulin IV over 4-6 hours on days -4 to -2. Patients undergoing umbilical cord blood transplantation will also receive low dose total-body irradiation on day -1. TRANSPLANTATION: Patients receive either bone marrow, peripheral blood stem cells (PBSC), or umbilical cord blood (UCB) from the donor on day 0. The use of either bone marrow, PBSC, or umbilical cord blood will depend on the donor status. IMMUNOSUPPRESSION: Patients receive a combination of immunosuppressive medications to try and prevent graft-versus-host disease. There are 2 regimens depending on the donor. Regimen A: Patients undergoing bone marrow or PBSC transplantation receive tacrolimus daily from day -1 to 50 followed by a taper until day 180 in the absence of GVHD. Patients also receive methotrexate IV on days 1, 3, 6, and 11. Regimen B: Patients undergoing UCB transplantation receive cyclosporine on days -3 to 100 followed by a taper until day 180 in the absence of GVHD. Patients also receive mycophenolate mofetil on days 0 to 40 followed by a taper until day 96 in the absence of GVHD. After completion of study treatment, patients are followed up periodically for 5 years.