Concomitant chromosome 5q-deletion and JAK2V617F mutation present with myelodysplastic and myeloproliferative overlap features

Myelodysplastic Syndrome (MDS) with an isolated deletion of chromosome 5q [del(5q)] is a relatively rare MDS variant (5%) characterized by a moderate to severe anemia and normal or elevated platelet count with modest neutropenia [1-3]. These latter features, in addition to its excellent response to lenalidomide, are likely what contribute for its favorable prognosis [3-5]. The somatic gain of function mutation in JAK2 V617F is a driving mutation in Myeloproliferative Neoplasms (MPN), occurring in 97% of polycythemia vera (PV), 50-60% of essential thrombocytosis (ET) and primary myelofibrosis (PMF) [6]. This mutation results in constitutive activation of the JAK-STAT signaling pathway leading to increased proliferation and hypersensitivity to cytokines erythropoietin, IL-3, thrombopoietin, and GCSF. An allelic burden of JAK2 V617F mutation correlates with an increased risk of thrombosis and hemorrhage, as well as secondary fibrosis in MPN patients [7].

Philadelphia chromosome positive chronic myeloid leukemia with 5q deletion at diagnosis

Background Although, molecular genetic analyses became more and more important to guide therapy decisions in leukemia, banding cytogenetic analysis has retained its vital role in diagnosis and monitoring of chronic myeloid leukemia (CML), by quick and easy enabling identification of pathognomonic Philadelphia chromosome (Ph). Case presentation A 45 year old female presented with characteristic hematological features of CML in chronic phase; cytogenetic studies revealed the presence of the typical Ph and a deletion of almost entire long arm of a chromosome 5. Conclusion 5q deletions have rarely been reported in CML. Those seen yet were either associated with tyrosine kinase inhibitor therapy or detected post allogeneic stem cell transplantation. To our knowledge, this is the first case of Ph positive CML accompanied by a 5q deletion.

Aromatase is a novel neosubstrate of cereblon responsible for immunomodulatory drug–induced thrombocytopenia

Immunomodulatory drugs (IMiDs) are key agents for the treatment of multiple myeloma and myelodysplastic syndrome with chromosome 5q deletion. IMiDs exert their pleiotropic effects through the recruitment of neosubstrates to cereblon, a substrate receptor of the E3 ubiquitin ligase complex; therefore, identification of cell-specific neosubstrates is important to understand the effects of IMiDs. In clinical practice, IMiDs induce thrombocytopenia, which frequently results in the discontinuation of IMiD treatment. In the current study, we sought to identify the molecular mechanism underlying thrombocytopenia induced by IMiD treatment. We found that IMiDs strongly impaired proplatelet formation, a critical step in functional platelet production, through the inhibition of autocrine estradiol signaling in human megakaryocytes. Furthermore, we identified aromatase, an indispensable enzyme for estradiol biosynthesis, as a novel neosubstrate of cereblon. IMiDs promoted the recruitment of aromatase to cereblon, resulting in the degradation of aromatase in a proteasome-dependent manner. Finally, aromatase was significantly degraded in the bone marrow of patients with multiple myeloma who developed thrombocytopenia with IMiD treatment. These data suggest that aromatase is a neosubstrate of cereblon that is responsible for IMiD-induced thrombocytopenia.