Transmembrane activator and calcium-modulator and cyclophilin-ligand interactor (TACI), encoded by TNFRSF13B, plays a central role in B cell maturation and antibody responses through its interactions with BAFF and APRIL, with variants being linked to common variable immunodeficiency (CVID) and selective IgA deficiency. To characterise the clinical, immunological and genetic spectrum of these individuals, we recruited 30 participants (21 patients and nine family members) and classified patients into Group 1 (n = 16), carrying only TACI variants and Group 2 (n = 5), carrying both an IEI-related variant and an additional TACI variant. With a male/female ratio of 12/9, the median age was 2 years at symptom onset and 14 years at genetic diagnosis. Common clinical manifestations included recurrent infections (90%), autoimmune/inflammatory features (62%) and lymphoproliferation (57%). Twelve distinct TNFRSF13B mutations were identified, predominantly clustering in the cysteine-rich domain 2 (CRD2), with Cys104Arg being the most frequent (57%) variant. Immunophenotyping revealed decreased switched-memory and marginal zone B cells, reduced naïve CD4+ T cells and increased effector memory subsets. Notably, clinical and laboratory features overlapped between Groups 1 and 2, as well as between monoallelic and biallelic TNFRSF13B variant carriers. Patients with TNFRSF13B variants display broad phenotypic heterogeneity ranging from asymptomatic carriage to CVID and combined immunodeficiency phenotypes. Given the high polymorphism ratio and incomplete penetrance observed, TACI acts as both a genetic modifier and a monogenic disease-causing gene in this cohort, suggesting that coexisting genetic variants and exposomal factors likely determine the clinical expression and disease severity.

BackgroundMajor histocompatibility complex (MHC) class II deficiency is a rare, life-threatening primary immunodeficiency that presents in early infancy with a SCID phenotype. However, emerging data indicate substantial clinical and immunological heterogeneity, including atypical presentations and neurological involvement.MethodsWe retrospectively evaluated the clinical, immunological, genetic, and treatment-related characteristics and outcomes of 22 patients from 19 unrelated families diagnosed with MHC class II deficiency at a single referral center (2000–2019). Ten patients underwent HSCT at our center; transplant-related outcomes were evaluated, and long-term follow-up data were available for the six surviving patients through 2025.ResultsThe median age at symptom onset and diagnosis was 9 and 12 months, respectively. Pneumonia, chronic diarrhea, and failure to thrive were the most common presenting features; neurological manifestations and developmental delay were observed in a subset of patients. Two patients showed residual HLA-DR expression and survived with a milder clinical course. CD4+ T cell lymphopenia and humoral dysfunction were consistent, while total lymphocyte counts were variable. RTE levels were mildly to moderately reduced in all tested patients, suggesting impaired thymic output. Severe viral infections were frequent and could be rapidly fatal. Fourteen patients required PICU admission, associated with high mortality. Genetic analysis (n:15) identified homozygous pathogenic variants in RFXANK (n=5), RFXAP (n=4), RFX5 (n=3), and CIITA (n=3). Ten patients underwent HSCT, with superior survival compared to non-transplanted patients (60% vs. 18%). Among transplanted patients, survival appeared higher following RTC than MAC (75% vs. 50%). Post-transplant mortality was observed in association with severe pre-transplant disease, delayed diagnosis, graft failure, and infectious complications. At ≥10 years post-HSCT, all survivors were IVIG-independent; CD4+ T cell recovery was higher after MAC than RTC, while T-cell chimerism remained mixed in both groups.ConclusionMHC class II deficiency is a SCID-like pediatric immunological emergency that is fatal without HSCT in most patients. Early diagnosis is critical, as initial infections may be rapidly progressive. HSCT provides durable engraftment and sustained clinical stability in long-term survivors. Incorporating HLA-DR expression analysis into first-line immunological screening, even in the absence of profound lymphopenia, may facilitate earlier diagnosis, prompt HSCT referral, and improve survival.

Inflammatory bowel disease (IBD) causes chronic suffering from gastrointestinal inflammation and dysfunction that can progress to colon cancer1,2. The prevalence of the disease is increasing, and there is an urgent need to better understand its pathogenic mechanisms to improve treatment. We show that GPR15-a G-protein-coupled receptor expressed in immune cells and described previously as an entry co-factor for human and simian immunodeficiency viruses3-is a marker and homing receptor for a subset of intramucosal GPR15-guided regulatory CD8+ T lymphocytes (CD8+ TIGR cells). Deleterious GPR15 gene variants in humans cause defective homing of CD8+ TIGR cells and are associated with severe early-onset IBD. Moreover, CD8+ TIGR cells are reduced in the intestinal mucosa of individuals with sporadic IBD. In mice, GPR15 deficiency impairs colonic homing of CD8+ TIGR cells, leading to accumulation of inflammatory macrophages and increased susceptibility to colitis. CD8+ TIGR cells potently kill macrophages activated by intestinal damage or disease using Fas ligand and TNF-related weak inducer of apoptosis (TWEAK). The identification of CD8+ TIGR cells yields new insights into organ-specific immune regulation and potential therapeutics for IBD.

BackgroundCongenital analbuminemia (CAA) is an ultrarare autosomal recessive disorder caused by biallelic pathogenic variants in the ALB gene, leading to absent or severely reduced serum albumin. Although historically considered a benign biochemical condition, emerging evidence suggests that pediatric CAA may be associated with clinically relevant multisystem manifestations.MethodsWe conducted a longitudinal integrative study involving five children from two kindreds, all with genetically confirmed CAA. Their clinical features were thoroughly documented, along with extended coagulation tests and immunological profiling.ResultsAll patients presented with persistent hypoalbuminemia, early-onset edema, gastrointestinal morbidity (frequently leading to misdiagnosis as protein-losing enteropathy), antenatal complications, recurrent respiratory infections, and dyslipidemia. Genetic testing revealed an ALB splice-site mutation (c.1428 + 2T > C) in one kindred and a novel homozygous frameshift insertion (p.Glu69Ter) in the second. Coagulation profiling identified a reproducible prothrombotic signature, including elevated fibrinogen, D-dimer, and strikingly increased FXI activity, with one patient suffering life-threatening cerebral thrombosis. Immunological evaluation demonstrated preserved leukocyte and lymphocyte counts, preserved or elevated IgG levels, variable antigen-specific vaccine responses, reduced kappa-deleting recombination excision circle values in the tested patients, and skewing of CD4⁺ T cells toward effector memory subsets, consistent with immune dysregulation rather than frank immunodeficiency.ConclusionsThis study provides detailed multisystem phenotyping of pediatric CAA and supports the view that CAA may present with clinically relevant gastrointestinal, metabolic, infectious, and hemostatic manifestations beyond isolated hypoalbuminemia. Early molecular diagnosis may reduce unnecessary invasive investigations and facilitate individualized monitoring for infectious and thrombotic complications. Larger multicenter studies with longitudinal follow-up and functional validation are required to confirm these findings.

BACKGROUND:Nonsteroidal anti-inflammatory drug (NSAID)-exacerbated respiratory disease (N-ERD) is a clinical syndrome characterized by chronic rhinosinusitis with nasal polyposis (CRSwNP), adult-onset asthma and hypersensitivity to NSAIDs. Long-term aspirin treatment after desensitization (ATAD) is used for clinical improvement in N-ERD patients. However, information on the potential effect of ATAD on the platelet-neutrophil aggregates (PNA) level in N-ERD patients is highly limited. OBJECTIVE:This study aimed to explore the impact of PNA on the pathogenesis of N-ERD and the potential effect of ATAD on N-ERD patient profiles from a platelet point-of-view. METHODS:Sixty-one individuals were enrolled, including 16 N-ERD patients with ATAD (ATAD+), 15 N-ERD patients without ATAD (ATAD-), 15 aspirin-tolerant asthma (ATA) patients, and 15 healthy controls (HCs). Lipid mediators classical in N-ERD, including urinary-LTE4 (uLTE4), prostaglandin-D2 (PGD2), and prostaglandin-E2 (PGE2) were assessed by ELISA. Platelet activation was estimated based on expression levels of sP-selectin, CD40L, Platelet Factor-4 (PF4), RANTES, Thromboxane-A2 (TXA2), PAF, 12-HETE in plasma levels by ELISA; and PNA percentage by flow cytometry. RESULTS:ATAD+; 12-HETE, and PF4 levels were remarkably low, while higher levels were determined in ATAD- and ATA groups. ATAD+; uLTE4 levels were positively correlated with 12-HETE. Another positive correlation was detected between sP-selectin and 12-HETE in ATAD-. Compared to HCs, it was found that among all N-ERD patients, significant increase in PNA. CONCLUSIONS:Plasma levels of PGE2, PF4, and 12-HETE appear to be affected by aspirin treatment. We believe that 12-HETE could play a significant role in the N-ERD pathogenesis by contributing to platelet activation.

BACKGROUND:Lipopolysaccharide-responsive beige-like anchor (LRBA) deficiency and cytotoxic T lymphocyte-associated protein 4 (CTLA-4) insufficiency are rare primary immune dysregulation disorders. Both conditions result from impaired maintenance of CTLA-4, a critical inhibitory checkpoint molecule. Despite the known benefits of abatacept (a CTLA-4-Ig fusion protein) treatment, its precise immunologic effects remain unclear. OBJECTIVE:We comprehensively investigated the effect of abatacept therapy on patients with LRBA deficiency and CTLA-4 insufficiency using an integrative multiomics approach. METHODS:The study combined longitudinal flow cytometry, targeted and single-cell transcriptomics, and plasma proteomics in patients receiving abatacept treatment. RESULTS:Abatacept treatment increased thymic output and expansion of naive T and B cells while reducing memory T-cell subsets, CD4+ T-cell cytokine production, and CD21low B cells. Multimodal transcriptomic and proteomic analyses revealed previously unrecognized immunopathogenic mechanisms, including increased CD28 and T-cell receptor signaling as well as compensatory upregulation of inhibitory checkpoint proteins (LAG3, TIGIT, ADORA2A, VSIR, HAVCR2) in response to CTLA-4 insufficiency. Proteomic profiling confirmed the upregulation of inflammatory mediators, including CHI3L1, CXCL13, and CSF1. Most of these transcriptomic and proteomic abnormalities were reversed after abatacept therapy; notably, gene signatures derived from lymphocytes exhibited greater normalization than those associated with myeloid cells. Furthermore, identified shared and disease-specific molecular signatures distinguished LRBA-deficient patients from those with CTLA-4 insufficiency, revealing more severe immune dysregulation in LRBA deficiency. Single-cell RNA sequencing validated the reversal of checkpoint dysregulation and the expression of inflammation-related genes across lymphoid and myeloid lineages. CONCLUSION:Abatacept effectively corrects key immune circuits in both diseases. This integrative systems-level approach offers new mechanisms and therapeutic targets, supporting personalized intervention strategies.

IgG4, the least abundant IgG subclass in humans, is increasingly recognised for its involvement in allergic and autoimmune pathologies. Its unique properties, such as the tendency to form half-molecules (one heavy chain and one light chain) and its generally non-inflammatory nature, distinguish it from other IgG subclasses. Its role in immune dysregulation is further underscored by a distinct disease entity called IgG4-related disease (IgG4-RD), a systemic fibroinflammatory disorder characterised by IgG4+ plasma cell tissue infiltration, storiform fibrosis and obliterative phlebitis, reflecting a dysregulated immune response affecting multiple organs. This review examines the current understanding of IgG4, its emerging roles in immune dysregulation and IgG4-RD, including clinical manifestations and treatment options. We also discuss the recent advances in understanding the genetic underpinnings of IgG4-RD, highlighting the significance of germline gene variants and implicated immune cell types. Finally, we explore future research directions, emphasising the need for deeper insights into pathogenesis, specific biomarkers and optimised treatment strategies.

Background: Signal transducer and activator of transcription 3 (STAT3) gain-of-function (GOF) disease presents with lymphoproliferation, autoimmunity, and failure to thrive. Although Janus kinase inhibitors have alleviated symptoms, their effects on disease pathogenesis remain unclear. Objective: We prospectively investigated the clinical, immunologic, and transcriptomic responses of 4 patients with STAT3 GOF under long-term ruxolitinib treatment. Methods: We conducted clinical and immunologic evaluations at baseline and after ruxolitinib treatment at 3, 8, 12, and more than 12 months. Our assessments included measurement of levels of circulating T follicular helper cells, regulatory T cells, and cytokines, as well as proliferation assays. Furthermore, we investigated the transcriptomic changes with treatment and conducted T-cell receptor sequencing. Results: Ruxolitinib achieved substantial control over the clinical manifestations. Posttreatment evaluations demonstrated a notable increase in naive CD4+ and CD8+ T-cell populations, alongside a significant reduction in effector memory T-cell levels. Additionally, there was a decrease in levels of circulating T follicular helper cells and double-negative T cells. Regulatory T-cell percentages and their canonical markers, which were already reduced before treatment, declined further with ruxolitinib. The treatment did not alter the production of IL-4, IL-17A, IL-10, and IFN-g cytokines by the CD4+ T cells. Importantly, ruxolitinib effectively normalized the previously dysregulated transcriptome profile in PBMCs, bringing it closer to that of healthy controls. This normalization was most striking in the downregulation of STAT3-targeted genes, interferon-related genes, myeloid cell activation, and cytotoxic effector CD8+ T-cell genes, with effects persisting for up to 12 months. Self-reactive T-cell indices based on T-cell receptor repertoire analysis revealed potential autoreactive cell clones in the patient samples. Conclusion: Ruxolitinib reversed cellular and transcriptomic signatures, enhancing our understanding of the disease's pathophysiology and highlighting essential immunologic markers for precise monitoring. (J Allergy Clin Immunol 2025;155:784-91.)

BackgroundPathogenic variants in ALOX12B, a crucial enzyme involved in epidermal lipid processing, are among the most common causes of autosomal recessive congenital ichthyosis (ARCI). Although traditionally considered a cutaneous disorder, the systemic immunological implications of ALOX12B deficiency remain poorly understood.ObjectivesWe aimed to broaden the dermatologic and immunologic spectrum of ALOX12B-associated ARCI by characterizing the clinical, immunologic, and genetic features of six patients from three consanguineous families.MethodsThis prospective study included six patients with ALOX12B-associated ARCI identified through whole-exome sequencing. Detailed dermatological evaluations, infection histories, immunoglobulin profiles, lymphocyte subset analyses, and vaccine response assessments were performed.ResultsAll patients exhibited early-onset generalized ichthyosis, ranging from delayed-onset lamellar ichthyosis to collodion membrane presentations accompanied by nonbullous erythroderma. Two distinct biallelic ALOX12B variants were identified: a novel p.Thr383Lys and the known p.Cys544Arg. Several patients demonstrated recurrent bacterial or fungal infections (n = 5), markedly elevated serum IgE levels (n = 4), and isolated abnormalities in vaccine responsiveness (n = 2). Lymphocyte counts and other immunoglobulin classes were generally preserved; however, decreased IgG levels were observed in one patient (P3.1). Intravenous immunoglobulin replacement therapy reduced the frequency of infections in patients (P1.1 and P1.2).ConclusionsOur findings suggest that ALOX12B-related ARCI may involve secondary immune dysregulation, driven by chronic compromise of the epidermal barrier. An immunologic evaluation is warranted in selected cases, particularly those with a history of susceptibility to infections. Multidisciplinary care, encompassing dermatology, immunology, and genetics, is crucial for achieving optimal outcomes in ARCI.

BACKGROUND:Dedicator of cytokinesis protein 8 (DOCK8) is a guanine nucleotide exchange factor highly expressed in, and critical for, the function of various innate and adaptive immune cells. DOCK8 deficiency leads to combined immunodeficiency characterized by susceptibility to infections, autoimmunity, and a severe Th2-type immune response. While dysfunction in various T cell subsets has been implicated in these phenotypes, a comprehensive analysis of the T-cell receptor (TCR) repertoire in these patients has not yet been documented. This study investigates the αβ TCR repertoire in DOCK8-deficient patients to identify features related to disease pathogenesis and explore the potential role of TCR repertoire alterations in disease development. METHODS:We compared immune repertoire profiles determined by high-throughput TCR sequencing of circulating CD4+ and CD8+ T cells from patients with DOCK8 deficiency (n = 10) to healthy controls (n = 7) and patients with ataxia-telangiectasia (AT) (n = 5). RESULTS:Different diversity analyses revealed a restricted TRA and TRB repertoire in both CD4+ and CD8+ T cells from DOCK8-deficient patients, with the restriction being more pronounced in CD8+ T cells. Skewed usage of individual variable (V) and joining (J) genes and potentially self-reactive CD8+ T cell clones, as determined by hydrophobicity and cysteine indices, were identified in DOCK8-deficient patients. CONCLUSION:Our study represents the most comprehensive immune repertoire analysis in DOCK8 deficiency. The identification of a significantly restricted αβ TCR repertoire, along with the detection of potentially autoreactive clones, highlights the crucial role of immune repertoire profiling in elucidating the pathogenesis of DOCK8 deficiency.

A homozygous missense mutation in the transferrin receptor 1 (TfR1), also known as CD71, leads to a rare inborn error of immunity (IEI) characterized by the impaired lymphocyte activation and proliferation due to defective iron uptake of cells. However, only one causative mutation (c.58T > C, p.Y20H) in the TFRC gene coding for TfR1 has been reported so far. We herein identified a new disease-causing homozygous germline mutation in the TFRC gene (c.64C > T, p.R22W) (referred to as TfR1R22W from now on) in a Turkish patient with combined immunodeficiency (CID). TfR1R22W results in impaired TfR1 internalization similar to previously defined TfR1Y20H mutation. We found that TfR1R22W is associated with severely restricted B and T lymphocyte clonal diversity and impaired T cell activation and cytokine production as well as defective mitochondrial oxidative phosphorylation in helper T cells. In addition, circulating NK, Treg, and MAIT cell populations were significantly decreased in the patient. Using whole transcriptome analysis, we found dysregulated immune homeostasis and novel biological processes associated with TfR1R22W. We also identified a considerable expansion of circulating low-density neutrophils (LDNs) in patient’s PBMCs. Overall, TfR1R22W mutation expands the current understanding of the IEI associated with TfR1 dysfunction and provides new insights underlying impaired immune function, lymphocyte diversity, and granulocyte homeostasis.

Molecular diagnosis of inborn errors of immunity (IEI) plays a critical role in determining patients' long-term prognosis, treatment options, and genetic counseling. Over the past decade, the broader utilization of next-generation sequencing (NGS) techniques in both research and clinical settings has facilitated the evaluation of a significant proportion of patients for gene variants associated with IEI. In addition to its role in diagnosing known gene defects, the application of high-throughput techniques such as targeted, exome, and genome sequencing has led to the identification of novel disease-causing genes. However, the results obtained from these different methods can vary depending on disease phenotypes or patient characteristics. In this study, we conducted whole-exome sequencing (WES) in a sizable cohort of IEI patients, consisting of 303 individuals from 21 different clinical immunology centers in Türkiye. Our analysis resulted in likely genetic diagnoses for 41.1% of the patients (122 out of 297), revealing 52 novel variants and uncovering potential new IEI genes in six patients. The significance of understanding outcomes across various IEI cohorts cannot be overstated, and we believe that our findings will make a valuable contribution to the existing literature and foster collaborative research between clinicians and basic science researchers.

Abstract Recombination activating genes (RAG)1 and RAG2 deficiency leads to combined T/B-cell deficiency with varying clinical presentations. This study aimed to define the clinical/laboratory spectrum of RAG1 and RAG2 deficiency. We retrospectively reviewed the clinical/laboratory data of 35 patients, grouped them as severe combined immunodeficiency (SCID), Omenn syndrome (OS), and delayed-onset combined immunodeficiency (CID) and reported nine novel mutations. The male/female ratio was 23/12. Median age of clinical manifestations was 1 months (mo) (0.5–2), 2 mo (1.25–5), and 14 mo (3.63–27), age at diagnosis was 4 mo (3–6), 4.5 mo (2.5–9.75), and 27 mo (14.5–70) in SCID (n = 25; 71.4%), OS (n = 5; 14.3%), and CID (n = 5; 14.3%) patients, respectively. Common clinical manifestations were recurrent sinopulmonary infections 82.9%, oral moniliasis 62.9%, diarrhea 51.4%, and eczema/dermatitis 42.9%. Autoimmune features were present in 31.4% of the patients; 80% were in CID patients. Lymphopenia was present in 92% of SCID, 80% of OS, and 80% of CID patients. All SCID and CID patients had low T (CD3, CD4, and CD8), low B, and increased NK cell numbers. Twenty-eight patients underwent hematopoietic stem cell transplantation (HSCT), whereas seven patients died before HSCT. Median age at HSCT was 7 mo (4–13.5). Survival differed in groups; maximum in SCID patients who had an HLA-matched family donor, minimum in OS. Totally 19 (54.3%) patients survived. Early molecular genetic studies will give both individualized therapy options, and a survival advantage because of timely diagnosis and treatment. Further improvement in therapeutic outcomes will be possible if clinicians gain time for HSCT.

Secondary lymphoid organs (SLOs) provide the confined microenvironment required for stromal cells to interact with immune cells to initiate adaptive immune responses resulting in B cell differentiation. Here, we studied three patients from two families with functional hyposplenism, absence of tonsils, and complete lymph node aplasia, leading to recurrent bacterial and viral infections. We identified biallelic loss-of-function mutations in LTBR, encoding the lymphotoxin beta receptor (LTβR), primarily expressed on stromal cells. Patients with LTβR deficiency had hypogammaglobulinemia, diminished memory B cells, regulatory and follicular T helper cells, and dysregulated expression of several tumor necrosis factor family members. B cell differentiation in an ex vivo coculture system was intact, implying that the observed B cell defects were not intrinsic in nature and instead resulted from LTβR-dependent stromal cell interaction signaling critical for SLO formation. Collectively, we define a human inborn error of immunity caused primarily by a stromal defect affecting the development and function of SLOs.

Background: Phosphoinositide 3 kinases (PI3K) are lipid kinases expressed in lympho-cytes/myeloid cells. PI3K/AKT/mTOR signaling defects present with recurrent infec -tions, autoimmunity, lymphoproliferation, and agammaglobulinemia.Objective: To characterize the PI3K/AKT/mTOR pathway defects and perform path -way analyses to assess novel variant pathogenicity. Methods: We included 12 patients (heterozygous PIK3CD (n= 9) and PIK3R1 (n= 1) (activated PI3K delta syndrome (APDS) with gain- of- function mutations) and homozy-gous PIK3R1 variant (n= 2)), performed clinical/laboratory/genetic evaluation, and flow cytometric PI3K/AKT/mTOR pathway analyses. Results: Median age at onset of complaints was 17.5 months (3 months to 12 years) and at diagnosis was 15.7 years (2.5-37) in APDS. Median diagnostic delay was 12.9 years (1.6-27). Recurrent respiratory tract infections (90%), lymphoproliferation (70%), autoimmune/inflammatory findings (60%), and allergy (40%) were common in APDS. Recurrent viral infections were present in 4/10 and malignancy (non- Hodgkin lymphoma and testicular yolk sac tumor) was present in 2/10 in APDS. Low CD4+ T cells(5/8) with increased CD4+ effector memory (8/8) and CD4+ TEMRA cells (6/8) were present in the given number of APDS patients. We diagnosed tubulointerstitial nephritis, Langerhans cell histiocytosis, and late- onset congenital adrenal hyperplasia in APDS. Allergic findings, lymphoproliferation/malignancy, and high IgM were pre -sent in the APDS but not in PIK3R1 deficiency. Low IgM/IgG/CD19+ B cell counts were characteristic in patients with PIK3R1 homozygous loss-of function mutations. Conclusion: Differential diagnosis with combined immunodeficiency and diseases of immune dysregulation make molecular genetic analysis crucial for diagnosing mTOR pathway defects. It is easy to differentiate APDS and homozygous PIK3R1 defects with specific laboratory features. Additionally, mTOR pathway functional analysis is a definitive diagnostic and pathogenicity assessment tool for novel APDS mutations.

Combined immunodeficiency due to CD70 deficiency is characterized by increased susceptibility to infections, hypogammaglobulinemia, and malignancy. These patients typically present with chronic Epstein Barr virus (EBV) viremia, severe EBV-related hemophagocytic lymphohistiocytosis, lymphoproliferation, and Hodgkin and non-Hodgkin lymphomas. Plasmablastic lymphoma (PBL) is an extremely rare malignancy in all ages and is predominantly seen in male adults with human immunodeficiency virus infection. EBV infection, immunosuppression, solid organ transplantation, and age-related immune deterioration are also suspected causes of PBL. Nevertheless, there is scarce data about its association with primary immunodeficiencies in the literature. Here, we present the first case of a CD70-deficient pediatric patient with PBL.

IKKα is a multifunctional serine/threonine kinase that controls various biological processes, either dependent on or independent of its kinase activity. However, the importance of the kinase function of IKKα in human physiology remains unknown since no biallelic variants disrupting its kinase activity have been reported. In this study, we present a homozygous germline missense variant in the kinase domain of IKKα, which is present in three children from two Turkish families. This variant, referred to as IKKαG167R, is in the activation segment of the kinase domain and affects the conserved (DF/LG) motif responsible for coordinating magnesium atoms for ATP binding. As a result, IKKαG167R abolishes the kinase activity of IKKα, leading to impaired activation of the non-canonical NF-κB pathway. Patients carrying IKKαG167R exhibit a range of immune system abnormalities, including the absence of secondary lymphoid organs, hypogammaglobulinemia and limited diversity of T and B cell receptors with evidence of autoreactivity. Overall, our findings indicate that, unlike a nonsense IKKα variant that results in early embryonic lethality in humans, the deficiency of IKKα's kinase activity is compatible with human life. However, it significantly disrupts the homeostasis of the immune system, underscoring the essential and non-redundant kinase function of IKKα in humans.

Paired box 1 (PAX1) deficiency has been reported in a small number of patients diagnosed with otofaciocervical syndrome type 2 (OFCS2). We described six new patients who demonstrated variable clinical penetrance. Reduced transcriptional activity of pathogenic variants confirmed partial or complete PAX1 deficiency. Thymic aplasia and hypoplasia were associated with impaired T cell immunity. Corrective treatment was required in 4/6 patients. Hematopoietic stem cell transplantation resulted in poor immune reconstitution with absent naïve T cells, contrasting with the superior recovery of T cell immunity after thymus transplantation. Normal ex vivo differentiation of PAX1-deficient CD34+ cells into mature T cells demonstrated the absence of a hematopoietic cell-intrinsic defect. New overlapping features with DiGeorge syndrome included primary hypoparathyroidism (n = 5) and congenital heart defects (n = 2), in line with PAX1 expression during early embryogenesis. Our results highlight new features of PAX1 deficiency, which are relevant to improving early diagnosis and identifying patients requiring corrective treatment.