Palacios-Ortega M, Guerra-Galán T, Jiménez-Huete A
… +26 more, García-Aznar JM, Pérez-Guzmán M, Mansilla-Ruiz MD, Mendiola ÁV, López CP, Hornero EM, Rodriguez AP, Cortijo AP, Zarzuela MP, Morales MM, Mandly EA, Cárdenas MC, Carrero A, García CJ, Bolaños E, Íñigo B, Medina F, de la Fuente E, Ochoa-Grullón J, García-Solís B, García-Carmona Y, Fernández-Arquero M, Benavente-Cuesta C, de Diego RP, Rider N, Sánchez-Ramón S
J Clin Immunol
· 2025 Feb · PMID 39918595
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Salami F, Shad TM, Fathi N
… +16 more, Mojtahedi H, Esmaeili M, Shahkarami S, Afrakoti LGMP, Amirifar P, Delavari S, Nosrati H, Razavi A, Ranjouri MR, Yousefpour M, Esfahani ZH, Azizi G, Ashrafi M, Rezaei N, Yazdani R, Abolhassani H
J Clin Immunol
· 2025 Jan · PMID 39853455
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BACKGROUND: Ataxia telangiectasia mutated (ATM) kinase plays a critical role in DNA double-strand break (DSB) repair. Ataxia telangiectasia (A-T) patients exhibit abnormalities in immunoglobulin isotype expression and cl...BACKGROUND: Ataxia telangiectasia mutated (ATM) kinase plays a critical role in DNA double-strand break (DSB) repair. Ataxia telangiectasia (A-T) patients exhibit abnormalities in immunoglobulin isotype expression and class switch recombination (CSR). This study investigates the role of residual ATM kinase expression and activity in the severity of A-T disease. METHODS: A-T patients with defined genetic diagnoses were classified based on CSR and based on the severity of their medical complications. Isolated peripheral blood mononuclear cells from any patient were evaluated before and after exposure to 0.5 Gy ionizing radiation for one minute. Western blotting was performed to identify the expression of ATM and phosphorylated ATM (p-ATM) proteins compared to age-sex-matched healthy controls. RESULTS: In severe A-T patients (n = 6), the majority (66.7%) had frameshift mutations, while 33.3% had nonsense mutations in the ATM gene. The mild group (n = 3) had two cases of splice errors and one missense mutation. All patients with CSR defect had elevated IgM serum levels, whereas all switched immunoglobulins were reduced in them. Expression of ATM and p-ATM proteins was significantly lower (p = 0.01) in all patients compared to healthy controls, both pre-and post- and post-radiation. Additionally, low ATM and p-ATM protein expression levels were linked with the clinical severity of patients but were not correlated with CSR defects. CONCLUSION: Expression and activation of ATM protein were defective in A-T patients compared to healthy controls. Altered expression of ATM and p-ATM proteins may have potential clinical implications for prognostic evaluation and symptom severity assessment in individuals with A-T.
Thouvenel CD, Tipton CM, Yamazaki Y
… +19 more, Zhang TT, Rylaarsdam S, Hom JR, Snead C, Zhu C, Li QZ, Lee YN, Kawai T, Haque N, Zimmermann MT, Ponnan SM, Jackson SW, James RG, Sanz I, Notarangelo LD, Torgerson TR, Ochs HD, Rawlings DJ, Allenspach EJ
J Clin Immunol
· 2025 Jan · PMID 39812873
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Reduced function or hypomorphic variants in recombination-activating genes (RAG) 1 or 2 result in a broad clinical phenotype including common variable immunodeficiency (CVID) and even adult-onset disease. Milder RAG vari...Reduced function or hypomorphic variants in recombination-activating genes (RAG) 1 or 2 result in a broad clinical phenotype including common variable immunodeficiency (CVID) and even adult-onset disease. Milder RAG variants are less characterized. Here we describe the longitudinal course of a milder combined RAG deficiency in 3 of 7 siblings sharing the same RAG2 mutations over a 50-year study. Whole-genome and repertoire sequencing, bacteriophage immunizations, and deep immunophenotyping were used to compare affected and unaffected family members. The clinical phenotype of three affected siblings with hypomorphic RAG deficiency ranged from combined immunodeficiency and early mortality to a late-onset CID with hyper-IgM phenotype. T cells were remarkably similar across affected siblings, yet CDR3 skewing and regulatory T cell defects were not observed. B cell analysis showed elevated unswitched CD27+ and CD21 cells as well as features of an autoreactive antibody repertoire and presence of secreted autoantibodies, yet no clinical autoimmunity was present. Most striking was an expanded polyclonal marginal zone-like B cell population (IgM+IgD+CD27+) utilizing the self-reactive unmutated VH4-34 receptor demonstrating that hypomorphic RAG deficiency can promote expansion of self-reactive B cells. This process, however, was not sufficient to trigger clinical autoimmunity. Utilizing multiple approaches, we functionally measured the specific RAG2 variant effects and assessed how selection and secondary triggers altered the BCR repertoire and immunophenotype overtime. Overall, we demonstrate a broad disease spectrum in siblings with identical hypomorphic RAG deficiency, highlighting that phenotypic divergence can result from expansion of IgM + memory B cells.
Walsh RB, McNaughton P, Nademi Z
… +14 more, Laberko A, Balashov D, Al-Mousa H, Arkwright PD, Wynn RF, Flood T, Williams E, Cant A, Abinun M, Hambleton S, Slatter M, Gennery AR, Lum SH, Owens S
J Clin Immunol
· 2025 Jan · PMID 39762600
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Receptor Interacting Serine/Threonine Kinase 1 (RIPK1) is widely expressed and integral to inflammatory and cell death responses. Autosomal recessive RIPK1-deficiency, due to biallelic loss of function mutations in RIPK1...Receptor Interacting Serine/Threonine Kinase 1 (RIPK1) is widely expressed and integral to inflammatory and cell death responses. Autosomal recessive RIPK1-deficiency, due to biallelic loss of function mutations in RIPK1, is a rare inborn error of immunity (IEI) resulting in uncontrolled necroptosis, apoptosis and inflammation. Although hematopoietic stem cell transplantation (HSCT) has been suggested as a potential curative therapy, the extent to which disease may be driven by extra-hematopoietic effects of RIPK1-deficiency, which are non-amenable to HSCT, is not clear. We present a multi-centre, international review of an additional 5 RIPK1-deficient children who underwent HSCT. All patients presented with very early onset inflammatory bowel disease, 2 also suffered from inflammatory arthritis. Median age at transplant was 3 years (range 1-5 years); 1 received matched sibling marrow, 1 matched unrelated peripheral blood stem cells (PBSC), 2 TCRαβ/CD19-depleted PBSC from maternal-haploidentical donors, and 1 had TCRαβ/CD19-depleted PBSC from a mismatched unrelated donor. All received reduced-toxicity conditioning, based on treosulfan (n = 4) or busulfan (n = 1); 1 patient underwent a successful second transplant following autologous reconstitution. Four of five patients (80%) survived; 1 child died due to multi-drug resistant pseudomonas infection and multi-organ failure. With a median duration of 14 months follow-up, 2 survivors were disease-free, and 2 had substantially improving enteropathy. These findings demonstrated that HSCT is a potential curative therapy for RIPK1-deficiency.
Fox TA, Massey V, Lever C
… +14 more, Pearce R, Laurence A, Grace S, Oliviero F, Workman S, Symes A, Lowe DM, Fiaccadori V, Hough R, Tadros S, Burns SO, Seidel MG, Carpenter B, Morris EC
J Clin Immunol
· 2025 Jan · PMID 39760904
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Allogeneic haematopoietic stem cell transplantation (alloHSCT) is safe and effective for adolescents and adults with inborn errors of immunity (IEI) with severe disease manifestations of their disease. The haematopoietic...Allogeneic haematopoietic stem cell transplantation (alloHSCT) is safe and effective for adolescents and adults with inborn errors of immunity (IEI) with severe disease manifestations of their disease. The haematopoietic cell transplantation comorbidity index (HCT-CI) score predicts transplant survival in non-malignant diseases, including IEIs. We hypothesised that immune dysregulation pre-transplant may also influence transplant outcomes. We calculated the pre-transplant immune dysregulation and disease activity score (IDDA v2.1) for 82 adolescent and adult IEI patients (aged ≥ 13 years). Three-year overall survival (OS) for the whole cohort was 90% (n = 82) with a median follow up of 44.7 months (range 8.4 to 225.8). Events were defined as acute graft-versus-host disease (GvHD) grades II or above, chronic GvHD of any grade, graft failure, or death from any cause. Three-year event free survival (EFS) for the whole cohort was 72%. In multivariable analysis the IDDA v2.1 score pre-transplant and HCT-CI score significantly impacted OS (hazard ratio 1.08, p = 0.028) and EFS (hazard ratio 1.04, p = 0.0005). Importantly, 35% of this cohort had a high IDDA v2.1 score (≥ 15) and low HCT-CI score (< 3) suggesting that the risks of alloHSCT may be underestimated in a proportion of patients with IEI if the HCT-CI score is used alone. These findings support the potential for improved outcomes following successful modulation of immune dysregulation pre-transplant. The IDDA v2.1 score has utility as an objective measurement of pre-transplant immune dysregulation providing additional information reagrding the risks and potential complications of alloHSCT in an individual IEI patient.
Major histocompatibility complex class I deficiency results from deleterious biallelic variants in TAP1, TAP2, TAPBP, and B2M genes. Only a few patients with variant-curated TAP1 deficiency (TAP1D) have been reported in...Major histocompatibility complex class I deficiency results from deleterious biallelic variants in TAP1, TAP2, TAPBP, and B2M genes. Only a few patients with variant-curated TAP1 deficiency (TAP1D) have been reported in the literature and the clinical phenotype has been variable with an emphasis on autoimmune and inflammatory complications. We report TAP1D in a Nepalese girl with a severe clinical phenotype with serious viral infections at a very young age. A novel frameshift termination variant near the protein's amino (N-) terminal was found. Variants in exon 1 of the TAP1 gene (as in our case) have not been reported previously. We also perform a brief review of TAP1D that hints at potential genotype-phenotype correlations. However, these findings need to be interpreted with due prudence given the small number of patients with TAP1D reported thus far.
Nikzad S, Johnson R, Scalchunes C
… +1 more, Rider NL
J Clin Immunol
· 2025 Jan · PMID 39747782
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PURPOSE: Patients with inborn errors of immunity (IEI) have lifelong health complications including severe infections and physical impairments. Previous studies show that a patient's perception of their health is an impo...PURPOSE: Patients with inborn errors of immunity (IEI) have lifelong health complications including severe infections and physical impairments. Previous studies show that a patient's perception of their health is an important predictor of health outcomes. The purpose of this study was to understand factors related to patient reported health status. METHODS: We used data from the Immunodeficiency Foundation (IDF) 2017 National Patient Survey and analyzed factors which correlated with the reported health status (RHS). Among a cohort of 1139 self-reported IEI patients, we identified age at the time of diagnosis, time gap between symptom onset and diagnosis, number of physicians seen, and whether the diagnosis was made in the first 5 years of life as significant. We used a two-tailed t-test, single-factor ANOVA, and Tukey-Kramer post-hoc test to assess statistical significance in the observed difference. RESULTS: Patients who received a diagnosis before the age of 12 had a significantly better mean RHS (n = 207 pre-12a vs. n = 900 post-12a; p < 0.0001). Patients who received a diagnosis within 10 years of symptom onset showed improved mean RHS (n = 413 pre-10 vs. n = 524 post-10; p < 0.0001). Among patients who had symptom onset within the first 5 years of life, those who received a diagnosis had a significantly improved RHS (3.5 ± 0.92, n = 275 undiagnosed vs. 2.8 ± 0.94, n = 108 diagnosed; p < 0.0001). Finally, RHS was significantly impacted by number of physicians(n ≥ 4) seen prior to diagnosis (3.1 ± 0.96 vs. 3.4 ± 0.80, p < 0.0001). CONCLUSION: These findings shed light upon critical factors which impact IEI patient RHS. Specifically, we find that efficient, rapid and early-life IEI identification should improve patient reported health and relevant outcomes. These improvements appear to be independent of the clinician specialty ultimately making the IEI diagnosis.
Inborn errors of immunity (IEI) are a heterogenous group of rare monogenic disorders that affect innate or adaptive immunity, resulting in susceptibility to life-threatening infections and autoimmunity. Allogeneic hemato...Inborn errors of immunity (IEI) are a heterogenous group of rare monogenic disorders that affect innate or adaptive immunity, resulting in susceptibility to life-threatening infections and autoimmunity. Allogeneic hematopoietic cell transplantation (HCT) is a valuable curative option for children with IEI. We conducted a retrospective single-center study on the outcome of HCT in children with IEI. Primary outcome was overall survival (OS). We gathered data from 55 patients underwent HCT in the period 2014 to 2023. The indications for HCT were CGD (n = 14), HLH (n = 12), SCID (n = 10), and others (n = 19). Median age at HCT was 3 years (range 0.1-17). Donors were HLA-matched related (n = 27), haploidentical (n = 24), and cord (n = 4). The conditioning regimens were myeloablative (n = 34), reduced intensity (n = 18), or no conditioning (n = 3). After a median follow-up of 43 months (range 13-120), 2-year OS was 93%, 2-year EFS 79% and 2 year GvHD-free relapse-free survival (GRFS) was 69%. Univariate analysis showed that bone marrow source was significantly associated with better EFS and GRFS. Cumulative incidence of grade 2-4 acute and moderate/severe chronic GvHD were 21% and 13%, respectively. Incidence of graft failure was 13%. In conclusion, HCT is feasible and curative in children with IEI. Early diagnosis and referral in addition to timely treatment can further improve outcomes.
Barzaghi F, Moratti M, Panza G
… +21 more, Rivalta B, Giardino G, De Rosa A, Baselli LA, Chinello M, Marzollo A, Montin D, Marinoni M, Costagliola G, Ricci S, Lodi L, Martire B, Milito C, Trizzino A, Tommasini A, Zecca M, Badolato R, Cancrini C, Lougaris V, Pignata C, Conti F
J Clin Immunol
· 2024 Dec · PMID 39714594
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BACKGROUND: Activated Phosphoinositide 3-Kinase (PI3K) δ Syndrome (APDS), an inborn error of immunity due to upregulation of the PI3K pathway, leads to recurrent infections and immune dysregulation (lymphoproliferation a...BACKGROUND: Activated Phosphoinositide 3-Kinase (PI3K) δ Syndrome (APDS), an inborn error of immunity due to upregulation of the PI3K pathway, leads to recurrent infections and immune dysregulation (lymphoproliferation and autoimmunity). METHODS: Clinical and genetic data of 28 APDS patients from 25 unrelated families were collected from fifteen Italian centers. RESULTS: Patients were genetically confirmed with APDS-1 (n = 20) or APDS-2 (n = 8), with pathogenic mutations in the PIK3CD or PIK3R1 genes. The median age at diagnosis was 15.5 years, with a median follow-up of 74 months (range 6-384). The main presenting symptoms were respiratory tract infections alone (57%) or associated with lymphoproliferation (17%). Later, non-clonal lymphoproliferation was the leading clinical sign (86%), followed by respiratory infections (79%) and gastrointestinal complications (43%). Malignant lymphoproliferative disorders, all EBV-encoding RNA (EBER)-positive at the histological analysis, occurred in 14% of patients aged 17-19 years, highlighting the role of EBV in lymphomagenesis in this disorder. Diffuse large B-cell lymphoma was the most frequent. Immunological work-up revealed combined T/B cell abnormalities in most patients. Treatment strategies included immunosuppression and PI3K/Akt/mTOR inhibitor therapy. Rapamycin, employed in 36% of patients, showed efficacy in controlling lymphoproliferation, while selective PI3Kδ inhibitor leniolisib, administered in 32% of patients, was beneficial on both infections and immune dysregulation. Additionally, three patients underwent successful HSCT due to recurrent infections despite ongoing prophylaxis or lymphoproliferation poorly responsive to Rapamycin. CONCLUSIONS: This study underscores the clinical heterogeneity and challenging diagnosis of APDS, highlighting the importance of multidisciplinary management tailored to individual needs and further supporting leniolisib efficacy.
Israni M, Alderson E, Mahlaoui N
… +22 more, Obici L, Rossi-Semerano L, Lachmann H, Avramovič MZ, Guffroy A, Dalm V, Rimmer R, Solis L, Villar C, Gennery AR, Skeffington S, Nordin J, Warnatz K, Korganow AS, Antón J, Cattalini M, Berg S, Soler-Palacin P, Campbell M, Burns SO, ESID Clinical Working Party, ERN RITA Transition Working Group Consortium
J Clin Immunol
· 2024 Dec · PMID 39690292
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PURPOSE: Significant improvements in the prognosis for young patients with Primary Immunodeficiency Diseases (PID) and Autoinflammatory Disorders (AID), which together make up the majority of Inborn Errors of Immunity (I...PURPOSE: Significant improvements in the prognosis for young patients with Primary Immunodeficiency Diseases (PID) and Autoinflammatory Disorders (AID), which together make up the majority of Inborn Errors of Immunity (IEI), have resulted in the need for optimisation of transition and transfer of care to adult services. Effective transition is crucial to improve health outcomes and treatment compliance among patients. Evaluations of existing transition programmes in European health centres identified the absence of disease-specific transition guidelines for PID and AID, as a challenge to the transition process. This research aimed to establish expert consensus statements for the transition of young patients with PID and AID to adult services. METHODS: This project used the Delphi method to establish mutual agreement for the proposed recommendations. A draft set of statements was developed following a literature review of existing transition programmes. Then the ERN RITA Transition Working Group convened to review the drafted recommendations and develop them into a survey. This survey was circulated among healthcare professionals to determine consensus using a five-point Likert scale, with the level of agreement set to 80% or greater. Statements that did not reach consensus were revised by the Working Group and recirculated among respondents. RESULTS: The initial survey received 93 responses from 68 centres across 23 countries, while the following survey outlining revised recommendations received 66 responses. The respondents agreed upon recommendations detailing the structure and administration of transition programmes, collaborative working with social systems, and contraindications to transfer of care. CONCLUSION: This paper sets out a comprehensive set of recommendations to optimise transitional care for PID and AID.
PURPOSE: Wiskott-Aldrich syndrome (WAS) is an X-linked genetic disorder characterized by distinctive features including microthrombocytopenia, eczema and recurrent infections. In the present study we report clinical, imm...PURPOSE: Wiskott-Aldrich syndrome (WAS) is an X-linked genetic disorder characterized by distinctive features including microthrombocytopenia, eczema and recurrent infections. In the present study we report clinical, immunological and molecular spectrum of 41 WAS patients diagnosed over last five years. METHODS: Clinical and family history was collected from case records. Comprehensive immunological assessments including lymphocyte subset analysis, and flow cytometry based evaluation of WAS protein (WASP) expressions were performed in patients along with evaluation of carrier status in mothers. Genetic analysis was carried out with either Sanger sequencing or targeted exome sequencing. RESULTS: The patients included in this study presented at a median age of 9.5 months, with two adult cases. Clinical manifestations encompassed thrombocytopenia, eczema, bleeding, diarrhea, respiratory tract infections, CMV infection, and malignancy. Immunological phenotype revealed T cell lymphopenia, B cell lymphopenia, and elevated IgE levels. Flow cytometry analysis of WASP was performed in 36 cases out of which 68.42% demonstrated complete absent expression while others showed reduced expression. Genetic analysis highlighted that the majority of mutations affect the WH1 domain of WASP while both adult patients showed intronic mutations. Molecular Dynamics analysis conducted for the novel variants P398R and G33R showed an average RMSD (Å) higher than that of the wild type, indicating greater structural perturbations in WASP. CONCLUSION: In the present study we have documented 56.09% novel WAS mutations in Indian cohort. Notably, the application of flow cytometry has emerged as a valuable and efficient diagnostic tool for identifying these WAS patients.
Takada S, Gallo S, Silva S
… +10 more, Tanaka H, Pincheira O, Zúñiga J, Villarroel M, Hidalgo X, Melo-Tanner J, Suzuki H, Machida S, Takahashi H, Miyake N
J Clin Immunol
· 2024 Dec · PMID 39673647
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Anterior gradient 2 (AGR2) is a protein disulfide isomerase that is important for protein processing in the endoplasmic reticulum and is essential for mucin production in the digestive and respiratory tracts. Bi-allelic...Anterior gradient 2 (AGR2) is a protein disulfide isomerase that is important for protein processing in the endoplasmic reticulum and is essential for mucin production in the digestive and respiratory tracts. Bi-allelic AGR2 variants were recently found to cause recurrent respiratory infections and failure to thrive with or without diarrhea (RIFTD; MIM # 620233), although the mechanisms behind this condition remain unclear. To date, at least 15 patients with homozygous AGR2 variants have been reported. Here, we report two affected siblings in a consanguineous family who had recurrent respiratory infections and digestive symptoms, one of whom needed lung transplantation. To identify the genetic cause of their symptoms, we performed exome sequencing and identified a novel homozygous missense variant in AGR2 (NM_006408.4, c.250A>C, p.(Ser84Arg)) in both affected siblings. Both parents had the identical variant in a heterozygous state. This variant is quite rare in the general population and is clinically compatible with RIFTD, substituting a highly conserved CXXS motif with CXXR. We performed structural modeling and functional studies to investigate the effect of this variant. Through transient overexpression, Ser84Arg AGR2 decreased protein stability, and promoted aberrant dimerization under non-reducing conditions. AGR2 functions in a monomer-dimer equilibrium. Size-exclusion chromatography showed that the Ser84Arg mutant had a larger molecular size than the wild-type protein under non-reducing, but not reducing conditions, indicating that Ser84Arg enhanced intermolecular disulfide bonds. In conclusion, we identified a novel pathogenic AGR2 variant and indicated its abnormal monomer-dimer equilibrium as a possible mechanism involved in the pathogenesis of RIFTD.
Chauvin SD, Holley JA, Poddar S
… +6 more, Miner CA, Kumble L, Fu J, Laue-Gizzi H, Hardy TA, Miner JJ
J Clin Immunol
· 2024 Dec · PMID 39671052
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TREX1 mutations underlie a variety of human diseases, including retinal vasculopathy with cerebral leukoencephalopathy (RVCL or RVCL-S), a catastrophic adult-onset vasculopathy that is often confused with multiple sclero...TREX1 mutations underlie a variety of human diseases, including retinal vasculopathy with cerebral leukoencephalopathy (RVCL or RVCL-S), a catastrophic adult-onset vasculopathy that is often confused with multiple sclerosis, systemic vasculitis, or systemic lupus erythematosus. Patients with RVCL develop brain, retinal, liver, and kidney disease around age 35-55, leading to premature death in 100% of patients expressing an autosomal dominant C-terminally truncated form of TREX1. We previously demonstrated that RVCL is characterized by high levels of DNA damage, premature cellular senescence, and risk of early-onset breast cancer before age 45. Here, we report human TREX1 mosaicism causing organ-limited RVCL in the retina, as well as a gene therapy to synthetically create TREX1 mosaicism as a potential treatment for RVCL. In our patient with organ-limited disease, the mosaic TREX1 mutant allele underwent germline transmission to 3 children, who developed severe multi-organ disease at ~ age 40, unlike their mosaic parent, who has organ-limited disease at age 74. Additionally, we describe our TREX1 prime editor gene therapy that corrects the most common RVCL-causing TREX1 variant in cell culture and in mice. Thus, TREX1 mosaicism causes organ-limited RVCL with a normal lifespan, suggesting that a gene therapy to create TREX1 mosaicism in adults may someday become useful as a treatment for patients with RVCL.
Zhen X, Betti MJ, Kars ME
… +14 more, Patterson AR, Medina-Torres EA, Scheffler Mendoza SC, Herrera Sánchez DA, Lopez-Herrera G, Svyryd Y, Mutchinick OM, Gamazon ER, Rathmell JC, Itan Y, Markle J, O'Farrill Romanillos P, Lugo-Reyes SO, Martinez-Barricarte R
J Clin Immunol
· 2024 Dec · PMID 39630167
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G6PC3 deficiency is a monogenic immunometabolic disorder that causes severe congenital neutropenia type 4. Patients display heterogeneous extra-hematological manifestations, contributing to delayed diagnosis. Here, we in...G6PC3 deficiency is a monogenic immunometabolic disorder that causes severe congenital neutropenia type 4. Patients display heterogeneous extra-hematological manifestations, contributing to delayed diagnosis. Here, we investigated the origin and functional consequence of the G6PC3 c.210delC variant found in patients of Mexican descent. Based on the shared haplotypes amongst mutation carriers, we estimated that this variant originated from a founder effect in a common ancestor. Furthermore, by ancestry analysis, we concluded that it appeared in the indigenous Mexican population. At the protein level, we showed that this frameshift mutation leads to an aberrant protein expression in overexpression and patient-derived Epstein-Barr Virus-immortalized B (EBV-B) cells. The neutropenia observed in G6PC3-deficient patients is driven by the intracellular accumulation of the metabolite 1,5-anhydroglucitol-6-phosphate (1,5-AG6P) that inhibits glycolysis. We characterized how the c.210delC variant impacts glycolysis by performing extracellular flux assays on patient-derived EBV-B cells. When treated with 1,5-anhydroglucitol (1,5-AG), the precursor to 1,5-AG6P, patient cells exhibited markedly reduced engagement of glycolysis. Finally, we compared the clinical presentation of patients with the mutation c.210delC and all other G6PC3-deficient patients reported in the literature, and we found that the c.210delC carriers display all prominent clinical features observed in prior patients. In conclusion, G6PC3 c.210delC is a loss-of-function mutation that arose from a founder effect in the indigenous Mexican population. These findings may facilitate the diagnosis of additional patients in this geographical area. Moreover, the in vitro 1,5-AG-dependent functional assay used in our study could be employed to assess the pathogenicity of additional G6PC3 variants.