Busulfan, Antithymocyte Globulin, and Fludarabine Followed By a Donor Stem Cell Transplant in Treating Young Patients With Blood Disorders, Bone Marrow Disorders, Chronic Myelogenous Leukemia in First Chronic Phase, or Acute Myeloid Leukemia in First Remission

DISEASE CHARACTERISTICS:

Diagnosis of one of the following hematopoietic disorders:

Severe aplastic anemia with marrow aplasia (i.e., absolute neutrophil count < 500/mm^3, platelet and/or red blood cell transfusion dependent), meeting 1 of the following criteria:

Closely matched related donor
Unresponsive to immunosuppressive therapy within 3 months after follow-up AND alternative matched unrelated donor available

Congenital marrow failure syndrome, including any of the following:

Primary red blood cell aplasia (Diamond-Blackfan syndrome)
Congenital neutropenia (Kostmann's syndrome)
Amegakaryocytic thrombocytopenia

Hemoglobinopathy including any of the following:

β-thalassemia major
Sickle cell anemia

Severe immunodeficiency disease including any of the following:

Chediak-Higashi disease
Wiskott-Aldrich syndrome
Combined immunodeficiency disease (Nezelof's)
Hyperimmunoglobulin M syndrome
Bare lymphocyte syndrome
Other stem cell defects (e.g., osteopetrosis)

Chronic myelogenous leukemia in first chronic phase

Not eligible for other ongoing phase II/III studies

Acute myeloid leukemia in first remission

Not eligible for other ongoing phase II/III studies
Inborn errors of metabolism
No severe combined immunodeficiency disorder

Available donor, meeting 1 of the following criteria:

Related donor matched by high resolution DNA typing at both HLA Drβ1 alleles and ≤ 1 mismatch at the 4 HLA-A and -B alleles

Unrelated donor, meeting one of the following criteria:

Bone marrow matched by high resolution DNA typing at both HLA Drβ1 alleles and ≤ 1 mismatch by high resolution DNA typing at the 4 HLA-A and -B alleles
Umbilical cord blood matched at 4/6 HLA-A, -B, and Drβ1 alleles by high resolution typing with ≥ 1 Drβ1 match and ≥ 3 X 10^7 cells/kg body weight of recipient

PATIENT CHARACTERISTICS:

See Disease Characteristics
No active bacterial, viral, or fungal infection
Cardiac shortening fraction ≥ 27%
Creatinine clearance ≥ 60 mL/min
DLCO ≥ 60% of predicted (corrected for anemia/lung volume)

PRIOR CONCURRENT THERAPY:

See Disease Characteristics