Genomic DNA Copy Number Alterations Present in AML Bone Marrow Samples with Normal Cytogenetics.

Cytogenetics and comparative genomic hybridization (CGH) have been used to identify large genomic amplifications and deletions in all subtypes of acute myeloid leukemia (AML). Up to 15–20% of AML patients have a normal karyotype at diagnosis. While cytogenetic abnormalities confer important prognostic information for patients with AML, there remain differences in the therapeutic response and outcome among patients with the same cytogenetic profile, implying that other, more subtle, genetic abnormalities may exist. We hypothesized that a subset of AML patients with normal cytogenetics may contain genomic DNA copy number changes that are too small to be detected using standard cytogenetic techniques. To address this possibility, we used high-resolution bacterial artificial chromosome (BAC) array CGH technology to examine 31 AML patients with normal cytogenetics. The BAC arrays contain 2,464 BAC clones spotted in triplicate on glass slides, and provide a 1 Mb resolution of the entire human genome. Technical generation of the arrays, hybridization parameters, and analysis were similar to that reported for murine BAC array CGH (Nat Genet. 2001 Dec;29(4):459–64). The 31 AML samples included 4 M0, 8 M1, 10 M2, and 9 M4 patients. Array CGH experiments were performed using 500 nanograms of Cyanine 5 labeled genomic DNA from unmanipulated AML bone marrow, mixed with an equal amount of control DNA (a pool of DNA from 4 cancer-free individuals) labeled with Cyanine 3. Using the human 1 Mb BAC arrays, we identified amplifications and deletions from multiple samples that were confirmed with G-banding cytogenetics [del(7)(q31), del(7)(p11.2), +8, del(11)(q13q23), +21, add(21)(q22), −X, −Y, +Y]. In addition, BAC arrays robustly detected copy number alterations that were identified in as few as 4/21 metaphases. We identified 5/31 (16%) patients with normal cytogenetics that contained altered genomic DNA copy numbers using BAC array CGH. Copy number changes were confirmed for several of these genomic loci using a dye-swap experiment, where the AML DNA was labeled with Cyanine 3, and the control DNA with Cyanine 5. Two of the 5 patients with abnormalities detected using array CGH would be reclassified from “intermediate” to “unfavorable” cytogenetics [del(7)(q31.31q34), add(11)(q23.3qter), and 17(p12pter)]. These results suggest that a subset of AML patients with normal cytogenetics contain genomic copy number alterations that may effect treatment and outcome.