Characterization of a t(10;12)(q24;p13) in a case of CML in transformation

We have used Southern blotting and fluorescence in situ hybridization (FISH) to define the breakpoints of a reciprocal translocation, t(10;12)(q24;p13), acquired as a secondary abnormality in a patient with Philadelphia chromosome positive chronic myeloid leukemia (CML) in transformation. A YAC clone that spanned the breakpoint at 12p13 was identified; this YAC included the CDKN1B gene but did not include ETV6. Neither ETV6 nor CDKN1B was rearranged, as determined by FISH and Southern blotting; however, a small deletion encompassing the translocated CDKN1B allele was detected. Analysis of two candidate genes at 10q24, HOX11 and NFKB2 suggested that they are not involved in this translocation. The preliminary mapping of breakpoints in this case demonstrated that they are different from an apparently identical translocation identified previously in a patient with myelodysplastic syndrome. The identification of the split YAC and small deletion should enable a more focused search for a gene or genes that may contribute to progression from chronic phase to blast crisis in CML.