GSE137496
Defective SEC61a1 underlies a novel cause of autosomal dominant severe congenital neutropenia
The molecular cause of severe congenital neutropenia (SCN) is unknown in 30-50% of patients. SEC61A1 encodes the a subunit of the heterotrimeric SEC61 complex, which governs endoplasmic reticulum (ER) signal peptide-dependent protein transport and passive calcium leakage. Recently, autosomal dominant mutations in SEC61A1 were reported to be pathogenic in common variable immunodeficiency (CVID) and glomerulocystic kidney disease. However the full spectrum of clinical manifestations in SEC61A1 mutations is yet to be explored. We investigated a SCN patient, the only child of healthy non-consanguineous Belgian parents. We identified a de novo private missense mutation in SEC61A1 (c.A275G;p.Q92R; CADD 24.5; msc 6.099) in the patient. The mutation results in diminished expression of the protein in PBMC and fibroblasts, and an increase in calcium leakage from the ER. In vitro differentiation of CD34+ cells recapitulated the patient's clinical arrest in granulopoiesis. The impact of Q92R-SEC61a1 on neutrophil maturation was validated using HL-60 cells, where transduction reduced differentiation into CD11b+CD16+ cells. A potential mechanism for this defect is the uncontrolled initiation of the unfolded protein stress response (UPR), with single-cell analysis of primary bone-marrow revealing perturbed UPR in myeloid precursors, and in vitro differentiation of primary CD34+ cells into neutrophils revealing upregulation of the pro-apoptotic CHOP and BiP UPR-response genes. Together, these results support specific autosomal dominant mutations in SEC61A1 causing SCN through dysregulation of the UPR. Overall design: Two RBC depleted whole bone marrow aspirates; one patient with severe congenital neutropenia with a de novo mutation in SEC61A1, one healthy gender-matched control