Hematopoietic stem cell transplantation (HSCT) has been established as an important therapeutic option for patients with a variety of inherited metabolic disorders (IMD). The potential life-threatening complications of conventional myeloablative HSCT have limited its application. Additionally, conventional HSCT is only available to the small minority of medically suitable candidates who have histocompatibility leukocyte antigen (HLA)-identical siblings to donate bone marrow or mobilized peripheral blood stem cells.