Molecular study on the chromosome 15 breakpoints in the translocation t(15; 17) in acute promyelocytic leukemia (APL).

Chromosomal translocation t(15; 17) is a specific marker of acute promyelocytic leukemia (APL). In this study, molecular cloning of the t(15; 17) breakpoint was carried out in a Chinese APL patient. It has been shown that the retinoic acid receptor alpha (RARA) gene, normally located on chromosome 17, was fused with a new transcription unit PML, normally localized on chromosome 15. We have subsequently cloned a portion of the PML gene and generated a panel of probes. A PML gene rearrangement was detected in 33 out of 36 APL cases studied. 24 rearrangements were clustered in a 4.4 kb region, designated here as PMLbcr1 whereas 9 rearrangements were concentrated in a 6.5 kb region, defining another breakpoint cluster region (PMLbcr2). These two types of rearrangement constitute the basis for the heterogeneity of the PML-RARA fusion gene and its possible biological significance remains to be explored.