A 12q13 translocation involving the HMGI-C gene in richter transformation of a chronic lymphocytic leukemia.

We report a case of Richter transformation of a chronic lymphocytic leukemia with a 12q13 translocation involving the HMGI-C gene. Fluorescence in situ hybridization analysis with the use of two different cosmid pools spanning the entire HMGI-C region showed that the breakpoint on chromosome 12 was located in the HMGI-C gene, presumably within intron 3. In fact, the 3' region of HMGI-C had been translocated to a derivative chromosome 6. This translocation was not visible at the cytogenetic level. Immunohistochemical analysis performed on the bone marrow smear demonstrated the expression of the HMGI-C protein specifically in the blasts, suggesting that the aberrant expression of the HMGI-C gene might have an important role in the process of leukemogenesis.