Defective Sec61α1 underlies a novel cause of autosomal dominant severe congenital neutropenia
Authors: Erika Van Nieuwenhove, John S. Barber, Julika Neumann, Elien Smeets, Mathijs Willemsen, Emanuela Pasciuto, Teresa Prezzemolo, Vasiliki Lagou, Laura Seldeslachts, Bert Malengier-Devlies, Mieke Metzemaekers, Sarah Haßdenteufel, Axelle Kerstens, Rob van der Kant, Frederic Rousseau, Joost Schymkowitz, Daniele Di Marino, Sven Lang, Richard Zimmermann, Susan Schlenner, Sebastian Munck, Paul Proost, Patrick Matthys, Christine Devalck, Nancy Boeckx, Frank Claessens, Carine Wouters, Stephanie Humblet-Baron, Isabelle Meyts, Adrian Liston
Journal: Journal of Allergy and Clinical Immunology (2020)

BackgroundThe molecular cause of severe congenital neutropenia (SCN) is unknown in 30% to 50% of patients. SEC61A1 encodes the α-subunit of the Sec61 complex, which governs endoplasmic reticulum protein transport and passive calcium leakage. Recently, mutations in SEC61A1 were reported to be pathogenic in common variable immunodeficiency and glomerulocystic kidney disease.ObjectiveOur aim was to expand the spectrum of SEC61A1-mediated disease to include autosomal dominant SCN.MethodsWhole exome sequencing findings were validated, and reported mutations were compared by Western blotting, Ca2+ flux assays, differentiation of transduced HL-60 cells, in vitro differentiation of primary CD34 cells, quantitative PCR for unfolded protein response (UPR) genes, and single-cell RNA sequencing on whole bone marrow.ResultsWe identified a novel de novo missense mutation in SEC61A1 (c.A275G;p.Q92R) in a patient with SCN who was born to nonconsanguineous Belgian parents. The mutation results in diminished protein expression, disturbed protein translocation, and an increase in calcium leakage from the endoplasmic reticulum. In vitro differentiation of CD34+ cells recapitulated the patient's clinical arrest in granulopoiesis. The impact of Q92R-Sec61α1 on neutrophil maturation was validated by using HL-60 cells, in which transduction reduced differentiation into CD11b+CD16+ cells. A potential mechanism for this defect is the uncontrolled initiation of the unfolded protein stress response, with single-cell analysis of primary bone marrow revealing perturbed UPR in myeloid precursors and in vitro differentiation of primary CD34+ cells revealing upregulation of CCAAT/enhancer-binding protein homologous protein and immunoglobulin heavy chain binding protein UPR-response genes.ConclusionSpecific mutations in SEC61A1 cause SCN through dysregulation of the UPR. The molecular cause of severe congenital neutropenia (SCN) is unknown in 30% to 50% of patients. SEC61A1 encodes the α-subunit of the Sec61 complex, which governs endoplasmic reticulum protein transport and passive calcium leakage. Recently, mutations in SEC61A1 were reported to be pathogenic in common variable immunodeficiency and glomerulocystic kidney disease. Our aim was to expand the spectrum of SEC61A1-mediated disease to include autosomal dominant SCN. Whole exome sequencing findings were validated, and reported mutations were compared by Western blotting, Ca2+ flux assays, differentiation of transduced HL-60 cells, in vitro differentiation of primary CD34 cells, quantitative PCR for unfolded protein response (UPR) genes, and single-cell RNA sequencing on whole bone marrow. We identified a novel de novo missense mutation in SEC61A1 (c.A275G;p.Q92R) in a patient with SCN who was born to nonconsanguineous Belgian parents. The mutation results in diminished protein expression, disturbed protein translocation, and an increase in calcium leakage from the endoplasmic reticulum. In vitro differentiation of CD34+ cells recapitulated the patient's clinical arrest in granulopoiesis. The impact of Q92R-Sec61α1 on neutrophil maturation was validated by using HL-60 cells, in which transduction reduced differentiation into CD11b+CD16+ cells. A potential mechanism for this defect is the uncontrolled initiation of the unfolded protein stress response, with single-cell analysis of primary bone marrow revealing perturbed UPR in myeloid precursors and in vitro differentiation of primary CD34+ cells revealing upregulation of CCAAT/enhancer-binding protein homologous protein and immunoglobulin heavy chain binding protein UPR-response genes. Specific mutations in SEC61A1 cause SCN through dysregulation of the UPR.