Alternative donor transplant has been performed commonly in patients with cancer, and also provides curative therapy for several non-malignant diseases (severe immunodeficiency, marrow failure and metabolic storage diseases). Alternate donor transplants carry higher risks of complications, including graft-versus-host disease, infection, and graft failure. Therefore, we will be selective about which patients are invited to participate, limiting eligibility to those patients that have had a severe SCD related problem (rather than those who are doing well and are likely to have few SCD related problems), but excluding patients who have such severe organ damage that they are more likely to die during transplant, and limiting eligibility to a young age group. A multi-step review algorithm that includes internal, local and external expert review has been constructed to provide a thorough, safe and ethical accrual process. We will treat patients using drugs and methods commonly used in alternate donor transplant for other diseases such as leukemia, and incorporate lessons learned from our previous experience in BMT for sickle cell by modifying supportive care measures. Special attention will be given to evaluation of post-BMT effects in this population, as well as potential reasons for adverse effects (such as graft failure).