Clofarabine and High-Dose Melphalan Followed by Donor Stem Cell Transplant in Patients With Acute Myeloid Leukemia, Acute Lymphocytic Leukemia, or Myelodysplastic Syndromes

DISEASE CHARACTERISTICS: * Diagnosis of one of the following: * Acute myeloid leukemia * Acute lymphocytic leukemia * Myelodysplastic syndromes * Disease meets 1 of the following criteria: * In first complete remission (CR) * In second CR * In relapse * No more than 50% blasts in bone marrow * Not deemed eligible for standard transplantation regimens by the attending physician, or at high risk for relapse * No suspected or proven CNS leukemia * HLA-matched (6/6) sibling donor available PATIENT CHARACTERISTICS: * Karnofsky performance status 50-100% * Glomerular filtration rate (pediatric patients) or creatinine clearance ≥ 60 mL/min OR serum creatinine \< 1.5 times upper limit of normal (ULN) * Serum bilirubin ≤ 2.0 mg/dL * AST and ALT ≤ 2.5 times ULN * LVEF ≥ 50% by ECHO or MUGA scan * DLCO or FEV\_1 ≥ 40% predicted * Not pregnant * Negative pregnancy test * No concurrent uncontrolled illness including, but not limited to, any of the following: * Ongoing, active, or poorly controlled infection * Symptomatic congestive heart failure * Unstable angina pectoris * Cardiac arrhythmia * Poorly controlled pulmonary disease * Psychiatric illness/social situation that would limit compliance with study requirement * No active cytomegalovirus (CMV) or fungal disease * HIV negative PRIOR CONCURRENT THERAPY: * Recovered from prior intensive chemotherapy (pediatric patients) * At least 100 days since prior autologous stem cell transplantation * At least 100…