Identification of von Willebrand factor D4 domain mutations in patients of Afro-Caribbean descent: In vitro characterization.

Background: Von Willebrand disease was diagnosed in two Afro-Caribbean patients and sequencing of the VWF gene (VWF) revealed the presence of multiple variants located throughout the gene, including variants located in the D4 domain of VWF: p.(Pro2145Thrfs*5) in one patient and p.(Cys2216Phefs*9) in the other patient. Interestingly, D4 variants have not been studied often. Objectives: Our goal was to characterize how the D4 variants p.(Pro2145Thrfs*5) and p.(Cys2216Phefs*9) influenced VWF biosynthesis/secretion and functions using in vitro assays. Methods: Recombinant VWF (rVWF), mutant or wild-type, was produced via transient transfection of the human embryonic kidney cell line 293T. The use of different tags for the wild-type and the mutant allele allowed us to distinguish between the two forms when measuring VWF antigen in medium and cell lysates. Binding of rVWF to its ligands, collagen, factor VIII, ADAMTS13, and platelet receptors was also investigated. Results: Homozygous expression of the p.(Cys2216Phefs*9)-rVWF mutation resulted in an almost complete intracellular retention of the protein. Heterozygous expression led to secretion of almost exclusively wild-type-rVWF, logically capable of normal interaction with the different ligands. In contrast, the p.(Pro2145Thrfs*5)-rVWF exhibited reduced binding to type III collagen and αIIbß3 integrin compared to wild-type-rVWF. Conclusions: We report two mutations of the D4 domains that induced combined qualitative and quantitative defects.

Germline ATG2B/GSKIP-containing 14q32 duplication predisposes to early clonal hematopoiesis leading to myeloid neoplasms.

The germline predisposition associated with the autosomal dominant inheritance of the 14q32 duplication implicating ATG2B/GSKIP genes is characterized by a wide clinical spectrum of myeloid neoplasms. We analyzed 12 asymptomatic carriers and 52 patients aged 18-74 years from six families, by targeted sequencing of 41 genes commonly mutated in myeloid malignancies. We found that 75% of healthy carriers displayed early clonal hematopoiesis mainly driven by TET2 mutations. Molecular landscapes of patients revealed two distinct routes of clonal expansion and leukemogenesis. The first route is characterized by the clonal dominance of myeloproliferative neoplasms (MPN)-driver events associated with TET2 mutations in half of cases and mutations affecting splicing and/or the RAS pathway in one-third of cases, leading to the early development of MPN, mostly essential thrombocythemia, with a high risk of transformation (50% after 10 years). The second route is distinguished by the absence of MPN-driver mutations and leads to AML without prior MPN. These patients mostly harbored a genomic landscape specific to acute myeloid leukemia secondary to myelodysplastic syndrome. An unexpected result was the total absence of DNMT3A mutations in this cohort. Our results suggest that the germline duplication constitutively mimics hematopoiesis aging by favoring TET2 clonal hematopoiesis.

Transcriptomic and genomic heterogeneity in blastic plasmacytoid dendritic cell neoplasms: from ontogeny to oncogenesis.

Oncogenesis and ontogeny of blastic plasmacytoid dendritic cell neoplasm (BPDCN) remain uncertain, between canonical plasmacytoid dendritic cells (pDCs) and AXL+ SIGLEC6+ DCs (AS-DCs). We compared 12 BPDCN to 164 acute leukemia by Affymetrix HG-U133 Plus 2.0 arrays: BPDCN were closer to B-cell acute lymphoblastic leukemia (ALL), with enrichment in pDC, B-cell signatures, vesicular transport, deubiquitination pathways, and AS-DC signatures, but only in some cases. Importantly, 1 T-cell ALL clustered with BPDCN, with compatible morphology, immunophenotype (cCD3+ sCD3- CD123+ cTCL1+ CD304+), and genetics. Many oncogenetic pathways are deregulated in BPDCN compared with normal pDC, such as cell-cycle kinases, and importantly, the transcription factor SOX4, involved in B ontogeny, pDC ontogeny, and cancer cell invasion. High-throughput sequencing (HaloPlex) showed myeloid mutations (TET2, 62%; ASXL1, 46%; ZRSR2, 31%) associated with lymphoid mutations (IKZF1), whereas single-nucleotide polymorphism (SNP) array (Affymetrix SNP array 6.0) revealed frequent losses (mean: 9 per patient) involving key hematological oncogenes (RB1, IKZF1/2/3, ETV6, NR3C1, CDKN2A/B, TP53) and immune response genes (IFNGR, TGFB, CLEC4C, IFNA cluster). Various markers suggest an AS-DC origin, but not in all patients, and some of these abnormalities are related to the leukemogenesis process, such as the 9p deletion, leading to decreased expression of genes encoding type I interferons. In addition, the AS-DC profile is only found in a subgroup of patients. Overall, the cellular ontogenic origin of BPDCN remains to be characterized, and these results highlight the heterogeneity of BPDCN, with a risk of a diagnostic trap.

Germline duplication of ATG2B and GSKIP predisposes to familial myeloid malignancies.

No major predisposition gene for familial myeloproliferative neoplasms (MPN) has been identified. Here we demonstrate that the autosomal dominant transmission of a 700-kb duplication in four genetically related families predisposes to myeloid malignancies, including MPN, frequently progressing to leukemia. Using induced pluripotent stem cells and primary cells, we demonstrate that overexpression of ATG2B and GSKIP enhances hematopoietic progenitor differentiation, including of megakaryocytes, by increasing progenitor sensitivity to thrombopoietin (TPO). ATG2B and GSKIP cooperate with acquired JAK2, MPL and CALR mutations during MPN development. Thus, the germline duplication may change the fitness of cells harboring signaling pathway mutations and increases the probability of disease development.