Identification of two atypical PML-RAR(alpha) transcripts in two patients with acute promyelocytic leukemia.

We identified two patients with atypical PML-RAR(alpha) rearrangements, 53 and 13 base pairs longer than the typical bcr1 transcript. Sequence analysis revealed a new PML breakpoint at the end of exon 7a in patient 1, and a PML exon 6 breakpoint in patient 2, with an insertion of 35 nucleotides of RAR(alpha) intron 2. Patient 1 did not express RAR(alpha)-PML and patient 2 showed the RAR(alpha)-PML transcript, which corresponded to the typical bcr1. These results emphasize on the relevance of the correct identification of atypical PML-RAR(alpha) rearrangements because of the potential implications in leukemogenesis, in the response to treatment, and for the correct monitoring of minimal residual disease.