MOLECULAR ANALYSIS OF THE PML RAR-ALPHA CHIMERIC GENE IN PEDIATRIC ACUTE PROMYELOCYTIC LEUKEMIA/

Acute promyelocytic leukemia (APL) is characterized cytogenetically by the t(15;17)(q22;q11-21) translocation. To compare molecular events a mong pediatric and adult APL cases, we designed two sets of oligonucle otide primers using published cDNA sequence for PML/RAR alpha fusion t ranscripts, and undertook reverse transcriptase-polymerase chain react ion (RT-PCR) analysis of 22 US pediatric cases of APL. PML/RAR alpha: fusion transcripts were detected in ail APL cases, including two cases lacking cytogenetic evidence of t(15;17). Breakpoint usage in PML was determined using a combination of PCR amplification with differing 5' primers, junction specific probes, and sequence analysis in selected cases. Consistent with previously published data, case analysis demons trated fusion products resulting from three breakpoint cluster regions (bcr) in PML, and a single breakpoint region in intron 2 of RAR alpha . transcripts resulting from breakpoints in bcr1 were detected in 59% of cases, bcr2 in 27% and bcr3 in 14%. This distribution is dissimilar to that observed in adults, where bcr2 comprises a lesser and bcr3 a greater portion of cases. These results suggest that the pathogenesis of the t(15;17) in APL may differ among patient sets. RT-PCR with thes e primer sets is a reliable method for detecting PML/RAR alpha chimeri c transcript in t(15;17)-containing APL.