Comparison of cytogenetics, Southern blotting, and fluorescence in situ hybridization as methods for detecting MLL gene rearrangements in children with acute leukemia and with 11q23 abnormalities

Bone marrow samples from 67 children with acute leukemia and with cytogenetic evidence of chromosome 11 band q23 (11q23) abnormalities were characterized by fluorescence in situ hybridization (flSH) and Southern blot analysis to determine whether FISH could reliably detect MLL gene rearrangements in this population. Among the 42 patients with acute lymphoblastic leukemia (ALL), MLL gene rearrangements were detected in cells from 23 patients (54.8%) by both FISH and Southern blot analysis. FISH identified allelic deletions of MLL gene in five of 12 patients (42%) with ALL and with deletion of 11q23. In 22 of 25 children (88%) with AML, FISH detected MLL gene rearrangements, whereas Southern blot analysis identified rearrangements in 24 of 25 patients (96%). For children with acute leukemia and with 11q23 abnormalities, we recommend that FISH be used for the rapid screening of MLL gene rearrangements and that Southern blot analysis be used for the definitive assessment of the MLL gene status.