Dek-can rearrangement in translocation (6;9)(p23;q34)

The translocation (6;9)(p23;q34) is mainly found in specific subtypes of acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). The diagnosis of this translocation is not easy since the cytogenetic change is quite subtle. The two genes involved in this translocation were recently isolated and diagnosis at the DNA-level became an additional option. Both the dek gene on chromosome 6 and the can gene on chromosome 9 contain one specific intron where breakpoints of t(6;9) patients were found to cluster. The translocation results in a consistent chimeric dek-can mRNA which is generated from the 6p- derivative. Five centers participated in a study to estimate the incidence of t(6;9) in leukemic patients using conventional Southern blot analysis. Patients (n = 320) with either acute undifferentiated leukemia (AUL), AML, MDS or acute lymphoblastic leukemia (ALL) were screened for rearrangement of the genes involved in this translocation. Four of these 320 patients showed rearrangement of the can gene on chromosome 9, of which one also had a rearranged dek gene on chromosome 6. A further 20 patients were studied with karyotypic aberrations in which either the short arm of chromosome 6 or the long arm of chromosome 9 were specifically involved. Both conventional Southern blot analysis and contour-clamped homogeneous electric field (CHEF) analysis failed to show dek-can rearrangement in any of these patients. The results of our study indicate that the incidence of the t(6;9) is a low as reported based on cytogenetic data and that rearrangement of the dek and can genes is mainly restricted to this specific translocation.