Study on Bone Marrow Transplant for Aplastic Anemia This study looks at using bone marrow transplants (BMT) to treat severe aplastic anemia (SAA), a rare condition where the body doesn't make enough blood cells. Blood cells are important as white blood cells fight infections, red blood cells carry oxygen, and platelets help stop bleeding. The study is for patients aged 3 to 75 who haven't been treated for SAA before. It uses marrow from compatible donors, even if they are not fully related. Participants will receive a special treatment to prepare their bodies for the transplant and will be monitored for one year after. Key Points: - Study involves 60 participants in total with donor bone marrow used for transplant. - Participants will receive a specific regimen of drugs and radiation to prepare for the transplant. - They will be followed for a year after the transplant to monitor results. Eligibility: Patients must be 3-75 years old, have a confirmed diagnosis of SAA, and lack a fully matched donor. They should also meet specific health criteria. Exclusions include previous SAA treatment, certain infections, and pregnancy.