Hematopoietic Stem Cell Transplant for Dyskeratosis Congenita or Severe Aplastic Anemia

Inclusion Criteria: * Aged 0 - 70 years * Acceptable hematopoeitic stem cell donor * Dyskeratosis Congenita (DC) with evidence of BM failure defined as: * requirement for red blood cell and/or platelet transfusions or * requirement for G-CSF or GM-CSF or erythropoietin or * refractory cytopenias having one of the following three * platelets \<50,000/uL or transfusion dependent * absolute neutrophil count \<500/uL without hematopoietic growth factor support * hemoglobin \<9g/uL or transfusion dependent * Diagnosis of DC with a triad of mucocutaneous features: * oral leukoplakia * nail dystrophy * abnormal reticular skin hyperpigmentation, or * Diagnosis of DC with one of the following: * short telomeres (under a research study) * mutation in telomerase holoenzyme (DKC1, TERT, TERC, NOP10, NHP2, TCAB1) * mutation in shelterin complex (TINF2) * mutation in telomere-capping complex (CTC1) * Severe Aplastic Anemia (SAA) primary transplant with evidence of BM failure: * Refractory cytopenia defined by bone marrow cellularity \<50% (with \< 30% residual hematopoietic cells) * Diagnosis of SAA with refractory cytopenias having one of the following three: * platelets \<20,000/uL or transfusion dependent * absolute neutrophil count \<500/uL without hematopoietic growth factor support * absolute reticulocyte count \<20,000/uL * Severe Aplastic Anemia (SAA) requiring a 2nd transplant * Graft failure as defined by blood/marrow chimerism of \< 5% * Early myelodysplastic features * With or without clonal cytogenetic abnormalities * Adequate organ function defined as: * cardiac: left ventricular ejection fraction ≥ 35% with no evidence of decompensated heart failure * pulmonary: DLCO ≥30% predicted, no supplemental oxygen requirement * renal: Glomerular filtration rate (GFR) ≥30% predicted * Voluntary written consent Exclusion Criteria: * Acute hepatitis or evidence of moderate or severe portal fibrosis or cirrhosis on biopsy * Pregnant or lactating * Uncontrolled infection * Prior radiation therapy (applies to SAA patients only) * Diagnosis of Fanconi anemia based on DEB * Diagnosis of dyskeratosis congenita with advanced MDS or acute myeloid leukemia with \>30% blasts