MLL amplification in acute leukaemia: a United Kingdom Cancer Cytogenetics Group (UKCCG) study

The MLL gene, located at 11q23, is frequently rearranged in acute leukaemia as either chimaeric fusion genes or partial tandem duplications. We report a series of 12 acute leukaemia cases with apparent amplification of the MLL gene ascertained using fluorescence in situ hybridisation (FISH). Seven cases showed intrachromosomal amplification of MLL, four cases showed extrachromosomal amplification as double minute chromosomes (dmin) and one case had separate subclones with dmin and homogenously staining region (hsr). Southern blot analysis of the MLL gene showed MLL gene rearrangement in three of the 10 successful cases. These cases do not naturally fall into either of the two recognised categories of MLL rearrangement and may represent a third variety of MLL gene abnormalities.