Mutations in GATA binding protein 2 (GATA2) lead to an immunodeficiency disease that transforms into myelodysplastic syndrome (MDS) and acute myelogenous leukemia (AML). This syndrome, previously known as MonoMAC, has 4 clinical features: 1) infections with Mycobacterium Avium Complex (MAC) and other opportunistic infections as a teenager or young adult, 2) a peripheral blood leukocyte flow cytometry profile with T-lymphocytes, but a severe deficiency of monocytes, B-lymphocytes, and Natural Killer (NK) cells, 3) the propensity to progress to MDS/AML, and 4) mutations in the gene GATA2. In this pilot study we propose to evaluate the efficacy and safety of a reduced intensity allogeneic hematopoietic stem cell transplantation (HSCT) regimen for patients with mutations in GATA2. We are particularly interested in determining whether allogeneic HSCT using this regimen reconstitutes normal hematopoiesis in patients with mutations in GATA2.