Deletion of exon b3 of the BCR gene in CML: easy breakpoint mapping by a two-round PCR

We have performed the molecular analysis for the detection of the BCR-ABL and ABL-BCR fusion genes in 50 patients with myeloproliferative disorders. All patients diagnosed with CML (13 out of 50) were positive for the BCR-ABL hybrid. Six CML patients (46%) showed ABL-BCR amplifications of the Ib-BCR type. All rearrangements but one were concordant. The aberrant case presented a deletion of exon b3, in addition to the alternative Ib-BCR and Ia-BCR. Its possible origin and relevance are briefly discussed.