Prevention of Bone Loss After Pediatric Hematopoietic Cell Transplantation

Inclusion Criteria: * Allogeneic hematopoietic cell transplant for hematologic malignancy (i.e. leukemia, lymphoma including ALL, AML, CML, NHL, HL) in complete remission; myelodysplastic syndrome (active dysplasia and/or blasts are permitted, but must not have active leukemia) or idiopathic severe aplastic anemia (SAA) * Non-malignant diseases including idiopathic severe aplastic anemia (SAA) and other bone marrow failure disorders, hemoglobinopathies, adrenoleukodystrophy, immune deficiencies/dysregulation disorders who will be receiving myeloablative or reduced toxicity preparative regimens that meet the following criteria: * Regimens include those that are TBI based if the TBI dose is \> 500cGy single dose or \> 800cGy fractionated, or doses \<500 cGy if combined with busulfan or treosulfan. These also include chemotherapy only based regimens that contain myeloablative doses of busulfan (\>8mg/kg) or treosulfan without TBI. * Patients with severe aplastic anemia are eligible regardless of conditioning regimen * Myeloablative preparative regimen (for SAA any conditioning therapy allowed) * Male or female ≥1 but ≤ 20 years of age at time of study enrollment * Patient or parent(s)/legal guardian(s) is able and willing to provide informed consent. Assent will be obtained per local institutional policy. Subjects who turn 18 during the course of the study will be consented at that time of their next visit by a member of the research staff. Exclusion Criteria: * History …