Comparison between Karyotyping-FISH-Reverse Transcription PCR and RNA-Sequencing-Fusion Gene Identification Programs in the Detection of KAT6A-CREBBP in Acute Myeloid Leukemia

An acute myeloid leukemia was suspected of having a t(8;16)(p11;p13) resulting in a KAT6A-CREBBP fusion because the bone marrow was packed with monoblasts showing marked erythrophagocytosis. The diagnostic karyotype was 46, XY, add(1)(p13), t(8;21)(p11;q22), der(16) t(1;16)(p13; p13)[9]/46, XY[1]; thus, no direct confirmation of the suspicion could be given although both 8p11 and 16p13 seemed to be rearranged. The leukemic cells were examined in two ways to find out whether a cryptic KAT6A-CREBBP was present. The first was the conventional approach: G-banding was followed by fluorescence in situ hybridization (FISH) and reverse transcription PCR (RT-PCR). The second was RNA-Seq followed by data analysis using FusionMap and FusionFinder programs with special emphasis on candidates located in the 1p13, 8p11, 16p13, and 21q22 breakpoints. FISH analysis indicated the presence of a KAT6A/CREBBP chimera. RT-PCR followed by Sanger sequencing of the amplified product showed that a chimeric KAT6A-CREBBP transcript was present in the patients bone marrow. Surprisingly, however, KATA6A-CREBBP was not among the 874 and 35 fusion transcripts identified by the FusionMap and FusionFinder programs, respectively, although 11 sequences of the raw RNA-sequencing data were KATA6A-CREBBP fragments. This illustrates that although many fusion transcripts can be found by RNA-Seq combined with FusionMap and FusionFinder, the pathogenetically essential fusion is not always picked up by the bioinformatic algorithms behind these programs. The present study not only illustrates potential pitfalls of current data analysis programs of whole transcriptome sequences which make them less useful as stand-alone techniques, but also that leukemia diagnosis still relies on integration of clinical, hematologic, and genetic disease features of which the former two by no means have become superfluous.