Rapid progression of myelofibrosis in polycythemia vera patient carrying SRSF2 c.284C>A p.(Pro95His) and unique ASXL1 splice site c.1720‐2A>G variant

Background The prognosis in polycythemia vera (PV) is comparatively favorable, but individual myelofibrosis/leukemic progression risk is heterogeneous. About a quarter of patients progress to the fibrotic phase after 20 years. Methods Multiplex PCR, allele‐specific qPCR, high‐resolution melt analysis, and Sanger sequencing were used to detect BCR‐ABL , JAK2 , ASXL1, SRSF2 , U2AF1 , and IDH1/2 variants. Results Herein, we present a PV patient with rapid progression to secondary myelofibrosis probably due to the coexistence of homozygous JAK2  V617F mutation, SRSF2 c.284C>A p.(Pro95His) and splice site variant of ASXL1 c.1720‐2A>G. The detected ASXL1 variant was first described in Bohring–Opitz syndrome and has not been reported in hematological malignancies so far. In the presented case, the ASXL1  VAF was stable (50%) during the 4‐year follow‐up, despite an evident increase in the JAK2  V617F VAF. Family history revealed cerebral palsy in the patient's grandson; however, germline character of the ASXL1 variant was excluded. Conclusion The biological consequences of the variant acquisition by hematopoietic stem cells (HSC) seem to be similar to other mutations of ASXL1 responsible for the truncation of ASXL1 protein, formation of hyperactive ASXL1–BAP1 (BRCA1‐associated protein‐1) complexes, and finally, the promotion of aberrant myeloid differentiation of HSC. Our report supports the hypothesis that ASXL1 alteration cooperates with JAK2 V617F leading to biased lineage skewing, favoring erythroid and megakaryocytic differentiation, accelerating the progression of PV to the fibrotic phase.