[Detection and localization of breakpoints within the first intron of the BCR gene in Ph1-positive leukemias].

We studied breakpoints within the first intron of the BCR gene in 28 Philadelphia (Ph1)-positive acute leukemias (AL) and one Ph1-positive chronic myelogenous leukemia (CML), which lacked rearrangement of major breakpoint cluster region. With a series of genomic probes from this intronic region, we have detected chromosomal breaks in 19 of 28 patients with Ph1-positive AL and one patient with CML. Breakpoints were all located within 30 kb region at the 3' portion of the intron, same as in the previously reported cases. Breakpoints in our cases were not limited within "bcr-2" or "bcr-3", proposed by Chen, et al., but, occurred within or near Alu sequences. Our findings suggest that breakpoints are not randomly distributed throughout this intron, but, there may be some specific sequences that facilitate the process of chromosomal translocation.