Alemtuzumab, Fludarabine, and Busulfan Followed By Donor Stem Cell Transplant in Treating Young Patients With Hematologic Disorders

DISEASE CHARACTERISTICS:

* Diagnosis of 1 of the following hematologic conditions:

  * Aplastic anemia with marrow aplasia, meeting all of the following criteria:

    * Absolute neutrophil count \< 500/mm\^3
    * Platelet and/or red cell transfusion dependent
  * Chronic aplastic anemia, meeting all of the following criteria:

    * Transfusion dependent
    * Unresponsive to immunosuppressive therapy
    * Alternative matched unrelated donor has been identified
  * Congenital marrow failure syndrome, including any of the following (with closely matched related or unrelated donor):

    * Primary red cell aplasia (Diamond-Blackfan syndrome)
    * Congenital neutropenia (Kostmann's syndrome)
    * Amegakaryocytic thrombocytopenia
    * Congenital dyserythropoietic anemias
    * Other severe acquired cytopenias in which a transplantation using a combined busulfan/cyclophosphamide conditioning regimen is indicated
  * Hemoglobinopathy (with closely matched related or unrelated donor)

    * β-thalassemia major
    * Sickle cell anemia
    * Hemoglobin E/β-thalassemia
  * Severe immunodeficiency disease

    * Chediak-Higashi disease
    * Wiskott-Aldrich syndrome
    * Combined immunodeficiency disease (Nezelof's)
    * Hyper immunoglobulin M (IgM) syndrome
    * Bare lymphocyte syndrome
    * Chronic granulomatous disease
    * Familial erythrohemophagocytic lymphohistiocytosis
  * Other stem cell defects (e.g., osteopetrosis)
  * Severe immune dysregulation/autoimmune disorders

    * Achieved a transient response to prior immunosuppressive therapy
  * Chronic myelogenous leukemia

    * Disease in first chronic phase
  * Acute myeloid leukemia

    * Disease in first remission
  * Myelodysplastic syndromes
  * Inborn errors of metabolism
  * Histiocytosis
* No severe combined immunodeficiency disease
* Matched related or unrelated donor available by high resolution DNA typing

  * Related donor, meeting both of the following criteria:

    * Matched at both human leukocyte antigen (HLA)-Drβ1 alleles
    * No more than 1 mismatch at the 4 HLA-A and -B alleles
  * Unrelated donor, meeting 1 of the following criteria:

    * Marrow matched at both HLA-Drβ1 alleles AND no more than 1 mismatch at the 4 HLA-A and -B alleles
    * Umbilical cord blood matched at 5/6 HLA-A, -B, and -DRβ1 alleles with at least 1 -DRβ1 match AND there are ≥ 3x10\^5 CD34+ (Cluster of differentiation 34-positive) cells per kg body weight of recipient available at the time of cryopreservation

PATIENT CHARACTERISTICS:

* Cardiac ejection fraction ≥ 27%
* Creatinine clearance ≥ 50 mL/min by 24-hour urine collection or glomerular filtration rate
* DLCO (diffusion capacity of lung for carbon monoxide) ≥ 50% of predicted (corrected for anemia/lung volume)

PRIOR CONCURRENT THERAPY:

* No prior transplantation for leukemia from which patient remains engrafted and alemtuzumab is not needed as part of the conditioning regimen