Sensitivity of FISH in detection of MLL translocations

Fluorescence in situ hybridisation (FISH) detection of MLL translocations i s now commonplace in cytogenetics laboratories. One of the most widely used probes is the Oncor MLL probe (Oncor, Gaithersburg, MD) that theoretically demonstrates the presence of an MLL rearrangement by a splitting of the FI SH signal between the two derivative chromosomes generated by a translocati on. Recently, another commercial probe has been made available from Vysis ( Vysis, Downers Grove, IL) that uses a dual colour system. We examined mater ial from 29 patients and 4 cell lines. all with recognised MU. translocatio ns by G-banding, that were confirmed using Southern blot analysis of the ML L breakpoint cluster region. Both Oncor and Vysis MLL FISH probes were appl ied to these cases to compare their performance in detection of the MLL tra nslocations. Thirty of the 33 cases demonstrated a clear splitting of Oncor MLL FISH signal in concordance with the Southern blot analysis and cytogen etics. Three cases failed to demonstrate a split MLL FISH signal. Therefore , we conclude that the Oncor MLL FISH probe has a 9.1% false negative rate, i.e., 90.9% sensitivity in detection of classic MLL translocations. Vysis MU. FISH detected the rearrangement in all 33 cases. (C) 2000 Wiley-Liss, I nc.