Mutations in MECOM, Encoding Oncoprotein EVI1, Cause Radioulnar Synostosis with Amegakaryocytic Thrombocytopenia

Abstract

Radioulnar synostosis with amegakaryocytic thrombocytopenia (RUSAT) is an inherited bone marrow failure syndrome, characterized by thrombocytopenia and congenital fusion of the radius and ulna. A heterozygous HOXA11 mutation has been identified in two unrelated families as a cause of RUSAT. However, HOXA11 mutations are absent in a number of individuals with RUSAT, which suggests that other genetic loci contribute to RUSAT. In the current study, we performed whole exome sequencing in an individual with RUSAT and her healthy parents and identified a de novo missense mutation in MECOM, encoding EVI1, in the individual with RUSAT. Subsequent analysis of MECOM in two other individuals with RUSAT revealed two additional missense mutations. These three mutations were clustered within the 8(th) zinc finger motif of the C-terminal zinc finger domain of EVI1. Chromatin immunoprecipitation and qPCR assays of the regions harboring the ETS-like motif that is known as an EVI1 binding site showed a reduction in immunoprecipitated DNA for two EVI1 mutants compared with wild-type EVI1. Furthermore, reporter assays showed that MECOM mutations led to alterations in both AP-1- and TGF-β-mediated transcriptional responses. These functional assays suggest that transcriptional dysregulation by mutant EVI1 could be associated with the development of RUSAT. We report missense mutations in MECOM resulting in a Mendelian disorder that provide compelling evidence for the critical role of EVI1 in normal hematopoiesis and in the development of forelimbs and fingers in humans.

MDS1 and EVI1 complex locus (MECOM): a novel candidate gene for hereditary hematological malignancies

“…Recently, three simplex patients showing a RUSAT phenotype were reported to carry de novo missense variants in ZF2, C2H2-type zinc finger motif 8 of MECOM (i.e., p.Arg750Trp, p.His751Arg, and p.Thr756Ala), which affect MDS1-EVI1 and EVI1 transcripts. The observed variants showed diminished target sequence binding and altered transcriptional regulation, 12 which is in line with our theoretical assumptions regarding the MECOM missense variant p.Cys766Gly. Herein, we report on the first family with autosomal dominant inheritance of a MECOM germline mutation in four patients spanning three generations.…”

MECOM-associated syndrome: a heterogeneous inherited bone marrow failure syndrome with amegakaryocytic thrombocytopenia

“…Primers for MPL, HOXA11, TERC, and MECOM were used as published previously. 2,6,10,11 Numbering of MECOM exons and designation of mutations refer to MECOM transcript variant 3 (NM_001105078.3) unless otherwise specified.…”

“…In 2015, Niihori et al 6 identified heterozygous mutations in MECOM (MDS1 and EVI1 complex locus) in 3 unrelated patients with RUS and AT (RUSAT2; MIM #616738). Recently, 2 other patients with RUSAT2 were described, 7,8 and Bluteau et al 9 identified 6 patients with MECOM mutations in a large cohort of patients with IBMFSs (supplemental Table 1).…”

Inherited platelet disorders: toward DNA-based diagnosis

“…HOXA11, 12 MECOM, 13 and GFI1B 14,15 ) expressed in hematopoietic stem and progenitor cells (Figure 2). Rare variants in RBM8A 16 and ANKRD26 17 have been shown to affect transcription factor binding (of Mecom and Runx1, respectively), altering signaling through the Thpo/Mpl pathway, and resulting in thrombocytopenia, but their exact role in megakaryopoiesis is not yet clear.…”