SF3B1, a Splicing Factor Gene, Is Infrequently Mutated in Rare Bone Marrow Failure Diseases but Still Associated with Ring Sideroblast Phenotype

Abstract 3485

Bone marrow failure syndromes (BMFS) are clonal diseases characterized by inefficient hematopoiesis leading to cytopenias. The clinical and biological heterogeneity often complicates therapy. A number of biological/genetic causes determine the pathogenesis of BMFS (immunological factors, cytokine, telomeres length, T-cell repertoire, epigenetic, apoptotic dysregulation, and chromosomal instability). Whole exome/genome sequencing identified novel mutations in myeloid disorders. SF3B1, a splicing factor gene is mutated primarily in myelodysplastic syndromes (MDS) with ring sideroblasts (RS). SF3B1 mutations brought to light the potential role of spliceosomes in MDS. Although, infrequent in other myeloid malignancies, SF3B1 mutations are relatively frequent in Fludarabine-resistant chronic lymphocytic leukemia (CLL) patients (pts). We previously reported 2 cases: myelofibrosis and paroxysmal nocturnal hemoglobinuria (PNH) with SF3B1 mutations and concomitant RS. To investigate the potential role of SF3B1 in the pathogenesis of rare BMFS, we screened a cohort of BMFS and other rare diseases (N=107): PNH, n=25, aplastic anemia (AA, n=17), T-large granular lymphocytic leukemia (T-LGL, n=17), pure red cell aplasia (PRCA, n=16), and mast cell disease (MCD, n=32) for SF3B1 mutations (exons 13–16) by Sanger sequencing. We identified SF3B1 mutations in 4 pts (MCD; n=2, A711D & K666T; PNH; n=1; K666Q; PRCA, n=1; K666N). Clinical history of the mutated cases showed that the 2 MCD pts fulfilled the criteria for cutaneous and indolent MCD. In the cutaneous MCD pt, skin biopsy revealed typical urticaria pigmentosa highlighting a dermal inflammation with increased MC. No infiltration of MC was found in the BM and no dysplasia was noted, except for RS (6%). In the 2^nd pt, the BM was hypocellular with clonal infiltration by MC. No other morphologic features were reported. Mutational analysis of genes implicated in diseases related to MCD, (c-KIT, TET2, IDH1/2, DNMT3A, EZH2, ASXL1, and CBL) showed a wild type configuration in both cases. The close association of MCD with chronic myelomonocytic leukemia (CMML) might explain SF3B1 mutations in the MCD pt as mutations in SF3B1 were reported in 6% of CMML. SF3B1 was also mutated in a pt with 10-year history of hemolytic PNH. BM pathology showed erythroid hyperplasia, no dysplasia, and increased RS (17%) in the BM. Perforin staining showed <0.1% positivity. Cytogenetic analysis showed a normal karyotype. No antecedent BM failure signs were found. The PNH clone was almost completely negative. Single-nucleotide polymorphism array showed the presence of a deletion of the X-chromosome in the PNH cell fraction (O'Keefe CL, Leukemia, 2011). Molecular screening detected absence of JAK2 which has been recently described to be harbored by pts with PNH and a deletion of Xp22.2 (Sugimori C, Blood Cell Cancer, 2012). PIG-A was not mutated. This case also underlines the association of SF3B1 and RS. In addition, SF3B1 could represent a second mutational event leading to PNH expansion in this case. Ultimately, we found SF3B1 mutated in a pt with acquired/PRCA. BM examination showed 50–60% cellularity, absence of erythroid precursors, and no overt sign of dysplasia. FISH analysis using MDS probes for chromosomes 5, 7, 8, and 20 was normal. The pt had increased platelets (470×10⁹/L), macrocytic anemia, and low reticulocytes. No RS was detected in the BM. It is possible that a lymphoproliferative process might be the cause for the presence of SF3B1 mutation. In conclusion SF3B1 is infrequently mutated in rare BMFS. The presence of SF3B1 mutations in cases with no RS might suggest underlying processes not associated with RS, like a lymphoproliferative process. Technical issues in the preparation of BM biopsy samples may also result in undue leaching of iron leading to false negativity reads after Prussian blue staining. It is also possible that sensitive techniques (transmission electron microscopy) may help detecting iron deposits in these cases. The hypocellularity of the BM and paucity of erythroid precursors typically seen in pts with BMF particularly in PRCA, may hamper accurate detection of RS. SF3B1 has been shown to predict better overall survival in pts with MDS and RS. All the mutated pts discussed in this abstract are still alive. The long-term follow up will clarify whether those pts will acquire additional mutational events or changes in their genetic content.