Fusion genes are frequently observed in hematologic malignancies and soft tissue sarcomas, and are usually associated with chromosome abnormalities. Many of these fusion genes create in-frame fusion transcripts that result in the production of fusion proteins, and some of which aid tumorigenesis. These fusion proteins are often associated with disease phenotype and clinical outcome, and act as markers for minimal residual disease and indicators of therapeutic targets. Here, we identified the 28S ribosomal DNA (RN28S1) gene as a novel fusion partner of the B-cell leukemia/lymphoma 11B gene (BCL11B), the immunoglobulin κ variable 3-20 gene (IGKV3-20) and the component of oligomeric Golgi complex 1 gene (COG1) in hematologic malignancies. The RN28S1-BCL11B fusion transcript was identified in a case with mixed-lineage (T/myeloid) acute leukemia having t(6;14)(q25;q32) by cDNA bubble PCR using BCL11B primers; however, the gene fused to BCL11B on 14q32 was not on 6q25. IGKV3-20-RN28S1 and COG1-RN28S1 fusion transcripts were identified in the Burkitt lymphoma cell line HBL-5, and the multiple myeloma cell line KMS-18. RN28S1 would not translate, and the breakpoints in partner genes of RN28S1 were within the coding exons, suggesting that disruption of fusion partners by fusion to RN28S1 is the possible mechanism of tumorigenesis. Although further analysis is needed to elucidate the mechanism(s) through which these RN28S1-related fusions play roles in tumorigenesis, our findings provide important insights into the role of rDNA function in human genomic architecture and tumorigenesis.

We describe a rare case of acute lymphoblastic leukemia in a 14-year-old female with congenital myotonic dystrophy manifested as mental retardation, extensive contractures of multiple joints of the lower extremities, and severe scoliosis. Because of the potential toxicity of chemotherapy and the patient's poor performance status, a modified chemotherapy regimen was administered. Analysis of the greatly expanded number of CTG repeats at the 3' untranslated region of DMPK gene showed that the number of repeats was 233 greater in leukemic cells than in normal lymphocytes; this elongation may have occurred during the cellular proliferation of leukemic clones.

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Acute lymphoblastic leukemia (ALL) occasionally develops before or after the onset of Langerhans cell histiocytosis (LCH). The mechanism of LCH developing after ALL remains unclear; thus the clonality of LCH developing during maintenance chemotherapy for T-cell ALL (T-ALL) was investigated. The T-ALL and LCH cells tested had the same T-cell receptor (TCR) gamma rearrangement. Mutation analysis of the NOTCH1 gene revealed 7213C>T (Q2405X) in exon 34 in T-ALL and LCH cells, but 5156T>C (I1719T) in exon 27 only in T-ALL. Polymerase chain reaction-restriction fragment length polymorphism analysis revealed three patterns of NOTCH1 mutations in T-ALL cells. The results suggest that the T-ALL and LCH cells were derived from a common precursor with TCR rearrangement and a single NOTCH1 mutation, rather than LCH cells developing from a minor clone of T-ALL with single NOTCH1 mutation.