Inborn errors of immunity (IEI), also known as primary immunodeficiencies, are a heterogeneous group of rare disorders characterized by increased susceptibility to infections, immune dysregulation, and malignancy. Early detection remains a major challenge due to the complexity of clinical presentations, limited awareness among non-specialists, and delayed diagnostic pathways. This review explores current strategies to enhance early detection of IEI, highlighting both technological innovations and clinical insights. Tools such as newborn screening, the Jeffrey Modell Foundation (JMF) warning signs, software like SPIRIT, and the PIDCAP project—a structured model designed for primary care implementation using ICD-coded clinical data— have shown promise in identifying at-risk patients. Artificial intelligence (AI) offers additional potential by detecting diagnostic patterns in electronic health records, although challenges related to data quality, heterogeneity, and system interoperability persist. Importantly, hematologic manifestations such as autoimmune cytopenias, lymphoproliferative disorders, and myelodysplastic syndromes often precede or accompany IEI and should prompt immunological evaluation. These conditions, frequently encountered in hematology, may serve as early clinical clues and justify genetic and immunophenotypic assessment. A multidisciplinary approach combining primary care, immunology, hematology, and AI technologies is essential to advance the early detection of IEI. Projects like PIDCAP, and their potential extension to secondary immunodeficiencies, exemplify scalable, patient-centered strategies that may significantly improve diagnostic timeliness and clinical outcomes.

Interleukin-33 (IL-33) is a central regulator of immune responses and inflammation, and genetic variation in IL33 and its receptor IL1RL1 (ST2) is strongly linked to disease susceptibility, notably asthma. Emerging evidence suggests that IL-33 also influences hematopoietic processes and platelet biology, indicating functions beyond canonical immunity. We investigated two missense variants identified in a patient with unexplained thrombocytopenia: a rare novel IL33 variant, c.385T>C (p.Tyr129His) and the common IL1RL1 variant c.1501_1502CA>AG (p.Gln501Arg), previously associated with reduced IL-33 signaling. Structural modeling revealed that IL-33 Y129H disrupts a conserved hydrogen bond within the IL-33/ST2/IL-1RAcP ternary complex, destabilizing receptor engagement. Functional assays confirmed markedly reduced binding affinity and biological activity, establishing Y129H as a loss-of-function variant. The IL1RL1 Q501R variant affects the Toll/IL-1 receptor (TIR) domain, critical for recruiting adapter proteins such as MyD88. Modeling revealed pronounced perturbation in a peripheral helix of the TIR domain, potentially impacting adapter recruitment and downstream signaling, providing a mechanistic basis for its protective association with asthma. Together, these findings provide structural and functional insights into clinically relevant IL33 and IL1RL1 variants. Their simultaneous occurrence in a patient with thrombocytopenia further supports a potential role for this pathway in platelet homeostasis and stress-responsive hematopoiesis.

ABSTRACT:Data on the immunosuppressants azathioprine (AZA) and mycophenolate mofetil (MMF) in autoimmune cytopenia (AIC) are limited, and no direct comparison exists. We analyzed the failure-free survival (FFS; time from AZA/MMF initiation to another non-first-line treatment, or death) of both treatments in the prospective nationwide pediatric OBS'CEREVANCE cohort. We included 343 patients (chronic immune thrombocytopenia, n = 161; autoimmune hemolytic anemia, n = 74; Evans syndrome, n = 108). They received AZA (n = 276) or MMF (n = 104; 37 sequentially received both) as monotherapy for a median duration of 11.3 (range, 0.01-149.0) months. Older age was associated with higher FFS for AZA, whereas secondary AIC was associated with higher FFS for MMF. AIC type had no effect. In a propensity score (PS)-matched cohort, AZA and MMF showed similar FFS (adjusted hazard ratio, 0.91; 95% confidence interval, 0.54-1.52; P = .71), with 1-year FFS rates of 73% and 76%, respectively. In subgroup analyses, AZA was associated with higher FFS in PS-matched patients diagnosed at an age of ≥10 years, whereas MMF was associated with higher FFS in PS-matched patients diagnosed at an age of <10 years and in those with confirmed secondary AIC (although with suboptimal matching). Rates of grade ≥3 infection were similar between the 2 drugs, at ∼2% new cases per year. In summary, AZA and MMF demonstrated comparable overall FFS and infection risk. However, our data suggest that AZA may be more beneficial in children diagnosed at an age of ≥10 years, whereas MMF may be more beneficial in those diagnosed at an age of <10 years and possibly in patients with secondary AIC.

Introduction:Histiocytic sarcoma (HS) is a rare neoplasm derived from non-Langerhans histiocytic cells, exceptionally arising from B-ALL. Methods:We present the case of a child with high-risk B-ALL with PAX5 P80R mutation. Results:Despite initial remission, a chemoresistant paravertebral mass was identified as HS. A shared IGK/TCRB rearrangements and PAX5 alterations between the leukaemic and histiocytic clones suggested transdifferentiation driven by PAX5. A somatic MAP2K1 mutation in the HS component prompted selumetinib treatment, leading to a rapid response. Conclusion:This case underscores the role of PAX5 in lineage plasticity and highlights the potential of targeted MEK inhibition in MAPK-driven HS arising from B-ALL. Trial Registration:The authors have confirmed clinical trial registration is not needed for this submission.

Autoimmune hemolytic anemia (AIHA) with an isolated C3d(+) direct antiglobulin test is a rare and understudied condition in children. It typically encompasses cold agglutinin syndrome and paroxysmal cold hemoglobinuria, both transient, infection-triggered disorders collectively referred to as cold AIHA. We report a national cohort of 142 pediatric patients with isolated C3d(+) AIHA, representing 21.6% of all childhood AIHA cases enrolled in the French OBS'CEREVANCE cohort over a 32-year period. The median age at diagnosis was 3.2 years (male-to-female ratio, 1.3), and median follow-up was 2.8 years. Infectious symptoms were present in 63.4% of cases. At diagnosis, median hemoglobin was 6.4 g/dL; 69.7% of patients had inadequate reticulocytosis (bone marrow responsiveness index of <121), and 90.4% required transfusions. Eighteen patients (12.7%) had or developed immunopathological manifestations (IM) including 5 diagnosed with primary immunodeficiency (4 with autoimmune lymphoproliferative syndrome). Among 8 (5.6%) patients with relapsing disease, 6 had no IM at diagnosis but 4 developed IM at relapse. Nine patients were antinuclear antibodies (ANA) positive; none progressed to systemic lupus over a median follow-up of 4.9 years. Corticosteroids were administered to 82.4% of patients (median duration, 4.5 months), with no clear benefit over untreated patients regarding hospital stay or transfusion needs. No deaths were reported. In conclusion, pediatric isolated C3d(+) AIHA generally follows a favorable course. However, a minority of patients may reveal underlying immune disorders, highlighting the importance of tailored evaluation at diagnosis. Cold agglutinin testing with thermal amplitude and Donath-Landsteiner testing, rarely performed in this cohort, warrant further study for their impact on diagnosis and clinical management.

Background Autoimmune neutropenia (AIN) is the main cause of chronic neutropenia in children, but its infectious consequences remain poorly studied. The primary objective of this study was to evaluate infectious events leading to emergency department or hospital admissions during the first 2 years following the diagnosis of AIN in children.Methods We performed a retrospective, multicentre analysis of medical records from 21 French university hospitals of patients aged under 18 years diagnosed with AIN with positive antineutrophils autoantibodies. We collected data on emergency room visits and hospitalisations in the 2 years following diagnosis, causes of these events, microbiology results, management and outcome.Results One hundred and sixty-eight patients were enrolled. Median age at diagnosis of AIN was 13 months. AIN was predominantly diagnosed during an infectious episode (n=120, 71%). In the 2 years of follow-up after diagnosis, 248 events of emergency room visits and/or hospitalisations were reported (0.77 per patient-year). The most frequent diagnoses were common childhood viral or bacterial infections. The incidence rate of severe infections was 0.003 per patient-year. Despite the predominance of viral infections, 177 episodes (71%) led to hospitalisation and 166 (68%) to the initiation of antibiotic therapy, for a median duration of 7 days (IQR 3-10).Conclusion The risk of severe infections in children with AIN is low. During follow-up, we suggest being attentive to signs of severity during fever, particularly in children over 3 years of age and/or with other immunological comorbidities but not proposing systematic hospitalisation or additional antibiotic therapy.

BACKGROUND:Children with very high-risk first relapse of B-cell acute lymphoblastic leukaemia have very poor outcomes with conventional chemotherapy. Inotuzumab ozogamicin has shown high antitumoral activity in second or higher relapsed or refractory B-cell acute lymphoblastic leukaemia. We aimed to evaluate the preliminary activity of inotuzumab ozogamicin single-agent in children with very high risk first B-cell acute lymphoblastic leukaemia relapse. METHODS:ITCC-059 was a multicentre, international, single-arm, phase 1-2 trial, designed to identify the recommended dose of inotuzumab ozogamicin (as monotherapy or with chemotherapy) for paediatric patients with relapsed or refractory CD22-positive acute lymphoblastic leukaemia, as previously reported, and to evaluate its activity and safety. An amendment to the original trial (April 26, 2021) introduced a third cohort, which enrolled patients at 20 hospitals across 12 countries, to evaluate the activity and safety of inotuzumab ozogamicin in children older than 1 year and younger than 18 years with CD22-positive very high risk first B-cell acute lymphoblastic leukaemia relapse and with a performance level of Karnofsky greater than 60% (for patients older than 16 years) or Lansky greater than 60% (for patients aged 16 years or younger). Very high risk relapse was defined as isolated bone marrow or combined relapse occurring less than 18 months after initial diagnosis or with cytogenetic or molecular high-risk characteristics (KTM2A::AFF1, TCF3::PBX1, TCF3::HLF, hypodiploidy, TP53mut/del). Patients were treated with intravenous inotuzumab ozogamicin at 1·8 mg/m2 in cycle 1 (0·8 mg/m2 on day 1, 0·5 mg/m2 on day 8, and 0·5 mg/m2 on day 15). Subsequent inotuzumab ozogamicin cycles were given to responding patients at a dose of 1·5 mg/m2 per cycle (0·5 mg/m2 on day 1, 0·5 mg/m2 on day 8, and 0·5 mg/m2 on day 15). A maximum of 6 cycles of inotuzumab ozogamicin were allowed. The primary endpoint for the phase 2 study for cohort 3 was the overall response rate, defined as the combined rate of patients with complete remission, complete remission with insufficient platelet recovery, and complete remission without recovery of counts as best response. Due to slow recruitment, the statistical design was amended to reduce the sample size. Recruitment continued until the amendment was approved by the competent authority (Feb 11, 2025), therefore response analysis for the primary endpoint was conducted only for the initial population that satisfied the amended minimum sample size. Safety outcomes were analysed in all patients who received at least one dose of the study drug and completed a baseline assessment and at least one post-baseline disease assessment. This trial is registered with the European Clinical Trials Information System, 2023-504694-20-00, and EudraCT, 2016-000227-71. Enrolment for cohort 3 of the study is complete, but follow-up is ongoing. FINDINGS:Between April 26, 2021, and Feb 11, 2025, 45 patients were screened for inclusion. Eight patients were excluded and 37 patients were enrolled and received treatment. Median age was 11 years (IQR 4-15); 22 (59%) of 37 patients were male and 15 (41%) were female. Among the first 31 enrolled patients (minimal amended sample size), 22 responded after treatment with inotuzumab ozogamicin (overall response rate 71%, 80% CI 58-82). All patients had at least one grade 3-4 haematologic laboratory test abnormality, with neutropenia (35 [95%] of 37 patients) and thrombocytopenia (31 patients [84%]), being the most common. The most common non-haematological grade 3-4 adverse events were febrile neutropenia (11 [30%] of 37 patients), infections (eight patients [22%], including one case of grade 5 lung infection), aspartate aminotransferase elevation (12 patients [32%]), and alanine aminotransferase elevation (ten patients [27%]). Serious adverse events occurred in 17 patients (46%). No treatment-related deaths occurred. Sinusoidal-obstructive-syndrome cases occurred in four (17%) of 23 transplanted patients, all of which resolved after intervention with defibrotide. INTERPRETATION:Inotuzumab ozogamicin showed high activity as reinduction treatment in paediatric very high risk first B-cell acute lymphoblastic leukaemia relapse and a favourable toxicity profile with no treatment-related deaths. FUNDING:Pfizer.

Homozygosity for rare loss-of-function IL23R variants abolishes IL-23-dependent IFN-γ production by lymphocytes, including NK and innate-like T cells, thereby underlying clinical disease due to weakly virulent mycobacterial species. We report selective enrichment in homozygosity for four hypomorphic IL23R variants in our cohort of patients with tuberculosis. Three of these IL23R alleles are rare (G300V, G149R and L372F), with a minor allele frequency (MAF) under 1%, but the fourth (R381Q) is surprisingly common, with a MAF as high as 10.2% in certain populations. The other 15 missense alleles found in the homozygous state in public databases are isomorphic. The four hypomorphic IL-23R variants identified dimerize with IL-12Rβ1 and bind IL-23. However, their function is impaired by low levels of cell-surface expression (R381Q, G300V) and/or as a consequence of conformational changes altering agonist efficacy. IFN-γ production in response to IL-23 is impaired in innate-like T cells and NK cells. These data suggest that recessive partial IL-23R deficiency, whether due to rare or common variants, confers a predisposition to tuberculosis while preserving immunity to less virulent mycobacteria. One sentence summary:Homozygous hypomorphic IL23R variants impair IL-23-dependent IFN-γ production and underlie tuberculosis.

The E3 ubiquitin ligase Casitas B-lineage lymphoma (CBL) promotes positive selection and antigen responses in mouse T lymphocytes by ubiquitinating ZAP70. Conversely, mouse CBL and CBL-B mutually redundantly regulate SYK ubiquitination and B cell receptor signaling. Here we studied individuals with somatically homozygous CBL loss-of-function variants in leukocytes. Human CBL is largely redundant for the development and function of human T cells. Conversely, B cell development is altered at the immature stage, with a tenfold increase in transitional cells, enhanced survival of autoreactive clones and impaired tolerance manifested by autoantibody production. B cell maturation is intrinsically impaired by reduced apoptosis and dysregulated B cell receptor signaling. CBL deficiency impairs humoral immunity by limiting memory B cell formation and reducing class switching and somatic hypermutation. Consequently, antigen-specific B cell generation and adaptive immune memory are disrupted, predisposing individuals to infection. Human CBL is critical for B cell development and function but redundant for T cell biology.

Acute leukemias represent the first cause of cancer in children. Their prognosis has improved significantly due to remarkable advances in therapeutic management, despite the risk of long-term consequences, especially for patients who underwent allogenic hematopoietic stem cell transplantation (aHSCT). Through the Leukemia in Children and Adolescents (LEA) long-term follow-up cohort (clinicaltrials gov. Identifier: NCT01756599), we conducted a French national multicenter prospective study on the occurrence and risk factors of chronic kidney disease (CKD), differentiating glomerular and tubular dysfunctions, corresponding to the NephroLEA project. Among the 1,676 patients included, the median age at evaluation was 15.8 (interquartile range [IQR], 11.3-20.5) years, with a median follow-up of 9.2 (IQR, 5.8-13.9) years. aHSCT was performed on 343 (20.6%) patients, half of whom have undergone the procedure after achieving second or greater remission. A higher percentage of children among transplanted patients had diastolic and systolic blood pressure above the 95th, with 13.7% versus 5.2% (P=3x10-3) and 15% versus 6.5% (P=9x10-2), respectively. A total of 187 patients (11.1%) had a mild CKD (i.e., eGFR between 75 and 90 mL/min/1.73 m2), while 3% (N=50) exhibited mild to severe CKD (eGFR <75 mL/min/1.73 m2). Notably, no patient reached kidney failure. Twenty-one patients (1.3%) had decreased glomerular filtration rate associated with tubular impairment. The principal risk factors for developing CKD were aHSCT and leukemia relapse. In conclusion, CKD represents a long-term risk for patients who relapsed and/or underwent aHSCT. These patients could benefit from nephroprotection advice to further improve their long-term outcomes, which is becoming a public health issue.

Omenn syndrome is a severe autosomal recessive combined immunodeficiency whose only curative treatment is allogeneic stem cell transplantation. We describe a rare case of infiltrative cardiomyopathy secondary to Omenn syndrome successfully treated by a combination of anti-IL5 antibodies and alemtuzumab, allowing successful HSCT.

Introduction: Treatment of acute promyelocytic leukemia (APL) has been revolutionized over the past two decades by the introduction of both all-trans retinoic acid (ATRA) and arsenic trioxide (ATO), leading to the use of chemotherapy-free protocols in standard-risk (SR) adult patients. In October 2019, a multicenter European pediatric trial from the International Consortium for Childhood (ICC) APL delivering a non-chemotherapy-based treatment for children with newly diagnosed SR and High Risk (HR) APL was started [NCT04793919]. Here, we report the results of the second planned interim analysis of the ICC-APL-02 study. Methods: ICC-APL-02 Study is an open-label prospective, non-randomized, multicenter trial for children and adolescents (up to the age of 18) with newly diagnosed APL delivering a risk-stratified treatment [according to the modified pediatric criteria (Testi, Blood 2018)] based on the use of ATRA and ATO, plus gemtuzumab ozogamicin (GO) only in HR patients. During induction, ATO was given at the dose of 0.15 mg/kg/day iv and ATRA at 25 mg/m2/day orally. Treatment started on day 1 and was continued until achievement of hematological complete remission (CR), for at least 28 days and for a maximum of 60 days. In HR patients only, GO was administered on days +2 and +4 of induction treatment, at the dose of 3 mg/m2 iv (maximum 5 mg/dose). During consolidation, ATO was given at the same dose employed during induction for 5 days/week, 4 weeks on and 4 weeks off, for 4 courses, while ATRA (25 mg/m2/day) was administered 2 weeks on and 2 weeks off for 7 courses. In the HR group only, triple intrathecal therapy was administered at the beginning of the 1st and 3rd consolidation. The primary endpoint was to evaluate the efficacy in terms of event-free survival (EFS) of the treatment regimen. Early death, death in CR, resistant disease and hematological relapse were considered as events. Results: The trial was opened in 52 centers across 5 countries (Italy, France, Czech Republic, Netherlands and Sweden). From 10/2019 to 06/2025, 110 patients were enrolled; 73 were SR (66.4%) and 37 HR (33.6%). Median white blood cell count at diagnosis for SR and HR patients was 2.5x109/L (0.6-9.9) and 18.0x109/L (10.55-151.00), respectively. Median age at diagnosis was 12 years (range 1-17); 45% of patients were females; 49% of patients were FLT3-ITD mutated. Median duration of induction was 37 days (range 28-59), with 36 patients (29 SR and 7 HR) interrupting the treatment for a median of 5 days (range 1-23), due to toxicity which resolved in all cases. During induction, 19 patients (17.3%) developed differentiation syndrome (DS) at a median time of 12 days (range 4-25) from treatment start, which resolved in all patients. Pseudotumor cerebri occurred in 14 patients (12.7%). Four patients experienced clinically-relevant prolongation of the QTc interval, which was successfully managed in all patients (in 3 with temporary ATO discontinuation). One patient developed myocarditis following GO which completely resolved without sequelae; no other drug-related side effect was registered. One 16-year old, FLT3-ITD+ HR patient died of cerebral hemorrhage during induction (day +30). All patients achieved hematological CR at the end of induction. All but one evaluated patients achieved molecular CR after the third consolidation course. The only positive patient (HR) remained MRD+ also after the end of treatment; he obtained the molecular remission with 2 additional doses of GO and was then treated with autologous hematopoietic stem cell transplantation; he is now alive and disease-free. One SR patient experienced molecular relapse 1 year after completing the treatment protocol; he was re-treated with ATRA-ATO and he is now alive with negative MRD. With a median follow-up of 21 months (range 2-68.7), the 2-yr overall and EFS of the whole cohort are 99% (95% CI 93.4-99.9) (SR 100% vs HR 97.1%, p=n.s.) and 96.4% (95% CI 88.6-98.9) (SR 97.4% vs HR 94.2%, p=n.s.), respectively. Nineteen patients are still on treatment. Conclusions: This is the first large prospective pediatric trial delivering a non-chemotherapy-based treatment for children with newly diagnosed SR and HR APL.We confirm that ATRA/ATO treatment is safe and highly effective in SR patients. More importantly, the combination of ATRA, ATO and GO in HR subjects showed an excellent safety profile and efficacy in pediatric patients with de novo APL.

A 6-month-old infant with Omenn syndrome and severe hypertrophic cardiomyopathy showed significant clinical improvement following multimodal immunosuppression with anti-IL-5 and alemtuzumab. This targeted approach successfully stabilized the patient, providing a critical bridge to curative hematopoietic stem cell transplantation.

Warm-antibody autoimmune hemolytic anemia (wAIHA) in children is a rare condition with limited data to predict outcomes or optimize therapy. Only two cohorts with more than 100 pediatric patients have been published. We took advantage of the national OBS'CEREVANCE cohort to clarify the long-term outcomes of wAIHA in children and determine whether initial clinical and biological characteristics are associated with distinct outcome patterns. We analyzed 241 children with wAIHA (excluding Evans syndrome) from the French multicenter OBS'CEREVANCE cohort (1990–2021) with a median follow-up of 4.7 years. Initial corticosteroid therapy was administered to 89% of patients. Among the 241 included patients, 42.2% (n=109) received subsequent-line therapy (SLT), with most (n=82) initiating treatment beyond 30 days (median time: 5.5 months, range 0–200 months). A total of 16.2% (n=39) received more than two lines of treatment. Rituximab was the most common second-line therapy (n=55), administered in 52.7% of cases within the first three months after diagnosis. One year post-diagnosis, 64.8% achieved complete remission without relapse (R) or SLT, including 19.9% still on corticosteroids. Meanwhile, 22.8% had SLT before corticosteroid discontinuation, and 12.4% relapsed after stopping corticosteroids. In the present study, we observed that SLTs were sometimes combined prematurely, before their optimal response window (6–8 weeks for rituximab, 3 months for immunosuppressants). While aggressive escalation may be justified in cases of severe, refractory hemolysis, each additional treatment increases infection risk, necessitates a careful risk-benefit assessment and appropriate anti-infective prophylaxis. During follow-up, 35.2% developed immunopathological manifestations (IM), including 10.3% with another autoimmune disease. A total of 15 patients (6.2%) were diagnosed with a primary immunodeficiency, with 5 diagnosed at the time of AIHA diagnosis and the remainder identified later. Identified PID cases during follow-up included ALPS, CVID, hyper IgM syndrome, and PID related to mutations in the following genes: RAG2, NFKB1, and ITK. Infectious complications were reported in 17.4% of patients, and two patients died. Among patients who received early rituximab within the first month, 17.6% relapsed or required subsequent-line therapy (R/SLT) after the expected 8-week response window. In patients treated with corticosteroids alone during the first month (77.5%), the cumulative incidence of relapse (CIR) or initiation of subsequent-line therapy (CIR-SLT) was 42.7% at 2 years and 46.2% at 5 years. Those with R/SLT were less likely to have inadequate reticulocytosis (33.7% vs 48.5%, P=0.03). Primary AIHA was more common in patients without R/SLT (72.3% vs 47.7%, P<0.001). An optimal corticosteroid duration to reduce CIR-SLT after discontinuation could not be determined. Interestingly, no patients had undergone splenectomy since 2010, reflecting a shift away from this approach in pediatric AIHA. These findings underscore the need for long-term follow-up and further study on corticosteroid duration and early SLT use. This study, the largest cohort analysis of pediatric wAIHA to date, provides valuable insights into treatment responses and long-term outcomes. Identifying underlying immune disorders, such as PID, at diagnosis, as well as associated IM, is crucial given their incidence in this population and their implications for tailored therapeutic management. While corticosteroids remain the cornerstone of treatment, nearly half of the patients required additional therapy. Future studies should focus on determining the optimal corticosteroid duration and evaluating the potential benefits of early rituximab use in childhood wAIHA, particularly in relation to associated IM and the prognostic value of BMRI at diagnosis.

Clinical laboratories searching for pathogenic variants focus mostly on the protein-coding region and corresponding essential splicing sites. Screening for variants in intronic regions requires dedicated bioinformatics tools and detailed experimental studies to confirm deleteriousness and pathogenicity. We report intronic variants in a cohort of eight patients from seven kindreds with unexplained inborn errors of immunity (IEI). Using ad hoc bioinformatics tools, we identified seven kindreds carrying three branchpoint variants at three loci (BTK, SH2D1A, and WAS) and four AG-gain acceptor site variants at another four loci (DOCK8, NFKB1, STXBP2, and UNC13D). The variants were located between positions −9 and −49 relative to the wild-type acceptor site. The deleteriousness and, thus, pathogenicity of these variants were confirmed by exon-captured transcriptome studies and flow cytometry analyses of protein production or function. Our findings indicate that intronic variants should be systematically screened and investigated, even in clinical laboratory settings.

GATA2 germline mutations lead to a syndrome characterized by immunodeficiency, vascular disorders and myeloid malignancies. To elucidate how these mutations affect hematopoietic homeostasis, we created a knock-in mouse model expressing the recurrent Gata2 R396Q missense mutation. Employing molecular and functional approaches, we investigated the mutation’s impact on hematopoiesis, revealing significant alterations in the hematopoietic stem and progenitor (HSPC) compartment in young age. These include increased LT-HSC numbers, reduced self-renewal potential, and impaired response to acute inflammatory stimuli. The mature HSPC compartment was primarily affected at the CMP sub-population level. In the mutant LT-HSC population, we identified an aberrant subpopulation strongly expressing CD150, resembling aging, but occurring prematurely. This population showed hyporesponsiveness, accumulated over time, and exhibited allele-specific expression (ASE) favoring the mutated Gata2 allele, also observed in GATA2 mutated patients. Our findings reveal the detrimental impact of a Gata2 recurrent missense mutation on the HSC compartment contributing to its functional decline. Defects in the CMP mature compartment, along with the inflammatory molecular signature, explain the loss of heterogeneity in HPC compartment observed in patients. Finally, our study provides a valuable model that recapitulates the ASE-related pathology observed in GATA2 deficiency, shedding light on the mechanisms contributing to the disease’s natural progression.