Background: An unclassified primary antibody deficiency (unPAD) is a widely heterogeneous clinical entity, recently identified within the spectrum of Inborn Errors of Immunity (IEIs). Since unPAD has been traditionally considered as a mild condition, it has incorrectly received little attention, resulting in the paucity of extensive and comparable studies describing its natural history. To address the gaps in characterizing, understanding, and managing pediatric unPAD patients, the Italian Primary Immunodeficiency Network (IPINet) Ped-unPAD study has recently been launched. Methods: Seventeen IPINeT Centers have expressed interest to participate, and data collection is still on-going. Hereby, we anticipate preliminary key issues emerging from the first 110 enrolled patients, attending three IPINet Centers. Results: A proportion of unPAD patients have experienced a severe infectious phenotype, which required hospitalization in a quarter of patients and antibiotic prophylaxis or Immunoglobulin Replacement Therapy in approximately 10% of patients. In this partial cohort, a mean follow-up (FU) of 5 years confirmed unPAD diagnosis in fifty percent of cases, with the remaining being reclassified as the Transient Hypogammaglobulinemia of Infancy (25%) and other IEIs (25%), such as a Common Variable Immunodeficiency, Selective IgA deficiency, Selective IgM deficiency, and IgG3 subclass deficiency. Conclusions: Despite a phenotype overlap at diagnosis, clinicians should be aware that unPAD is a mutable condition that deserves comprehensive evaluation and long-term monitoring to dissect the final diagnosis for optimal treatment.

UNASSIGNED: X-linked agammaglobulinemia (XLA) is a humoral immunodeficiency disorder characterized by recurrent infections, severe hypogammaglobulinemia, and a deficiency of circulating B cells. While the hallmark clinical manifestations of XLA typically include the respiratory, dermatological, and gastrointestinal systems, renal involvement is infrequent. In this article, we report two cases of XLA with concurrent renal disease, supplemented with a review of documented cases.
UNASSIGNED: The two cases described involve twin brothers, both presenting with respiratory tract infections and renal manifestations. Subsequent genetic testing confirmed the diagnosis of XLA. The younger brother exhibited improvement following intravenous immunoglobulin (IVIG) therapy and anti-infection treatment. Due to financial constraints, the older brother received only anti-infection and symptomatic treatments. Seven months after discharge, the older brother developed nephritis. However, he showed improvement following IVIG treatment.
UNASSIGNED: Immune profiling and genetic testing should be considered in male children with recurrent infections to facilitate the effective diagnosis of XLA. Regular monitoring is also imperative to detect and treat immune-mediated renal diseases in patients with XLA.

Children with severe inflammatory diseases are challenging to diagnose and treat, and the etiology of disease often remains unexplained. Here we present DIAPH1 deficiency as an unexpected genetic finding in a child with fatal inflammatory bowel disease who also displayed complex neurological and developmental phenotypes. Bi-allelic mutations of DIAPH1 were first described in patients with a severe neurological phenotype including microcephaly, intellectual disability, seizures, and blindness. Recent findings have expanded the clinical phenotype of DIAPH1 deficiency to include severe susceptibility to infections, placing this monogenic disease amongst the etiologies of inborn errors of immunity. Immune phenotypes in DIAPH1 deficiency are largely driven aberrant lymphocyte activation, particularly the failure to form an effective immune synapse in T cells. We present the case of a child with a novel homozygous deletion in DIAPH1, leading to a premature truncation in the Lasso domain of the protein. Unlike other cases of DIAPH1 deficiency, this patient did not have seizures or lung infections. Her major immune-related clinical symptoms were inflammation and enteropathy, diarrhea and failure to thrive. This patient did not show T or B cell lymphopenia but did have dramatically reduced naïve CD4+ and CD8+ T cells, expanded CD4-CD8- T cells, and elevated IgE. Similar to other cases of DIAPH1 deficiency, this patient had non-hematological phenotypes including microcephaly, developmental delay, and impaired vision. This patient\'s symptSoms of immune dysregulation were not successfully controlled and were ultimately fatal. This case expands the clinical spectrum of DIAPH1 deficiency and reveals that autoimmune or inflammatory enteropathy may be the most prominent immunological manifestation of disease.

In order to maintain the polio eradication status, it has become evident that the surveillance of cases with acute flaccid paralysis and of environmental samples must be urgently supplemented with the surveillance of poliovirus excretions among individuals with inborn errors of immunity (IEI). All children with IEI were screened for the excretion of poliovirus during a collaborative study conducted by the ICMR-National Institute of Virology, Mumbai Unit, ICMR-National Institute of Immunohaematology, and World Health Organization, India. A seven-month -old male baby who presented with persistent pneumonia and lymphopenia was found to have severe combined immune deficiency (SCID) due to a missense variant in the RAG1 gene. He had received OPV at birth and at 20 weeks. Four stool samples collected at 4 weekly intervals yielded iVDPV type 1. The child\'s father, an asymptomatic 32-year-old male, was also found to be excreting iVDPV. A haploidentical hematopoietic stem cell transplant was performed, but the child succumbed due to severe myocarditis and pneumonia three weeks later. We report a rare case of transmission of iVDPV from an individual with IEI to a healthy household contact, demonstrating the threat of the spread of iVDPV from persons with IEI and the necessity to develop effective antivirals.

BACKGROUND: Severe combined immunodeficiency (SCID) is a life-threatening genetic disorder caused by critical defects of the immune system. Almost all cases are lethal if not treated within the first two years of life. Early diagnosis and intervention are thus essential for improving patient outcomes. In 2013, Ontario became the first Canadian province to perform newborn screening (NBS) for SCID by T cell receptor excision circles (TRECs) analysis, a surrogate marker of thymic function and lymphocyte maturation.
METHODS: This retrospective study reports on nearly 10 years of NBS for SCID at a quaternary referral centre.
RESULTS: From August 2013 to April 2023, our centre\'s densely populated catchment area flagged 162 newborns with low TRECs levels, including 10 cases with SCID. Follow-up revealed other causes of low TRECs, including non-SCID T cell lymphopenia (secondary/reversible or idiopathic causes, and syndromic conditions) and prematurity. A small number of cases with normal repeat TRECs levels and/or T cell subsets were also flagged. Province-wide data from around this period revealed at least 24 diagnosed cases of SCID or Leaky SCID.
CONCLUSIONS: This is the first report of NBS outcomes in a Canadian province describing the causative genetic defects, and the non-SCID causes of a positive NBS for SCID.

G6PC3 deficiency is a monogenic immunometabolic disorder that causes syndromic congenital neutropenia. 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 origin. Based on the shared haplotypes amongst carriers of the c.210delC mutation, we estimated that this variant originated from a founder effect in a common ancestor. Furthermore, by ancestry analysis, we concluded that it originated 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 cells. G6PC3 pathology is driven by the intracellular accumulation of the metabolite 1,5-anhydroglucitol-6-phosphate (1,5-AG6P) that inhibits glycolysis. We characterized how the variant c.210delC impacts glycolysis by performing extracellular flux assays on patient-derived cells. When treated with 1,5-anhydroglucitol (1,5-AG), the precursor to 1,5-AG6P, patient-derived 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 to date, and we found that c.210delC carriers display all prominent clinical features observed in prior G6PC3 deficient 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.

Immunodeficiency, Centromeric instability and Facial anomalies (ICF) syndrome is a rare genetic disorder characterized by variable immunodeficiency. More than half of the affected individuals show mild to severe intellectual disability at early onset. This disorder is genetically heterogeneous and ZBTB24 is the causative gene of the subtype 2, accounting for about 30% of the ICF cases. ZBTB24 is a multifaceted transcription factor belonging to the Zinc-finger and BTB domain-containing protein family, which are key regulators of developmental processes. Aberrant DNA methylation is the main molecular hallmark of ICF syndrome. The functional link between ZBTB24 deficiency and DNA methylation errors is still elusive. Here, we generated a novel ICF2 disease model by deriving induced pluripotent stem cells (iPSCs) from peripheral CD34+-blood cells of a patient homozygous for the p.Cys408Gly mutation, the most frequent missense mutation in ICF2 patients and which is associated with a broad clinical spectrum. The mutation affects a conserved cysteine of the ZBTB24 zinc-finger domain, perturbing its function as transcriptional activator. ICF2-iPSCs recapitulate the methylation defects associated with ZBTB24 deficiency, including centromeric hypomethylation. We validated that the mutated ZBTB24 protein loses its ability to directly activate expression of CDCA7 and other target genes in the patient-derived iPSCs. Upon hematopoietic differentiation, ICF2-iPSCs showed decreased vitality and a lower percentage of CD34+/CD43+/CD45+ progenitors. Overall, the ICF2-iPSC model is highly relevant to explore the role of ZBTB24 in DNA methylation homeostasis and provides a tool to investigate the early molecular events linking ZBTB24 deficiency to the ICF2 clinical phenotype.

Inborn errors of immunity (IEI) are a group of diseases in humans that typically present as increased susceptibility to infections, autoimmunity, hyperinflammation, allergy, and in some cases malignancy. Among newly identified genes linked to IEIs include 3 independent reports of 9 individuals from 7 independent kindreds with severe primary immunodeficiency disease (PID) and autoimmunity due to loss-of-function mutations in the NCKAP1L gene encoding Hematopoietic protein 1 (HEM1). HEM1 is a hematopoietic cell specific component of the WASp family verprolin homologous (WAVE) regulatory complex (WRC), which acts downstream of multiple immune receptors to stimulate actin nucleation and polymerization of filamentous actin (F-actin). The polymerization and branching of F-actin is critical for creating force-generating cytoskeletal structures which drive most active cellular processes including migration, adhesion, immune synapse formation, and phagocytosis. Branched actin networks at the cell cortex have also been implicated in acting as a barrier to regulate inappropriate vesicle (e.g. cytokine) secretion and spontaneous antigen receptor crosslinking. Given the importance of the actin cytoskeleton in most or all hematopoietic cells, it is not surprising that HEM1 deficient children present with a complex clinical picture that involves overlapping features of immunodeficiency and autoimmunity. In this review, we will provide an overview of what is known about the molecular and cellular functions of HEM1 and the WRC in immune and other cells. We will describe the common clinicopathological features and immunophenotypes of HEM1 deficiency in humans and provide detailed comparative descriptions of what has been learned about Hem1 disruption using constitutive and immune cell-specific mouse knockout models. Finally, we discuss future perspectives and important areas for investigation regarding HEM1 and the WRC.

Common variable immunodeficiency is a heterogeneous symptomatic group of inborn errors of immunity that mainly affects antibodies production and/or function, predisposing patients to recurrent and severe infections. More than half of them usually develop autoimmunity, lymphoproliferation, enteropathy, and malignancies. Among these conditions, chronic lung disease such as granulomatous-lymphocytic interstitial lung disease is one of the leading causes of death in these patients. Recently, many genes that play a key role in B and T cells\' development, maintenance, and/or cytokines signaling pathways have been implicated in the pathogenesis of the disease. Here, we describe the first Argentinian patient presenting with common variable immunodeficiency and granulomatous-lymphocytic interstitial lung disease, harboring two in cis heterozygous variants in the SOCS1 gene.

UNASSIGNED: Newborn screening (NBS) for the early detection of inborn errors of immunity (IEI) has been implemented in a few countries. The objective of this study was to verify the situation and define obstacles to the implementation of NBS worldwide.
UNASSIGNED: A questionnaire was developed by the Inborn Errors of Immunity Committee of the World Allergy Organization (WAO) with 17 questions regarding NBS for IEI in the physician\'s workplace, NBS test type, problems hindering NBS implementation, reimbursement for IEI therapy, presence of a national IEI registry, referral centers, molecular diagnosis, hematopoietic stem cell transplantation centers, gene therapy, and immunoglobulin replacement therapy. The survey was sent by email once a week to doctors and others associated with WAO and the main immunology societies worldwide as a Google Form™ to be completed during September and October 2021.
UNASSIGNED: Two hundred twenty-nine questionnaires were completed, of which 216 (94.3%) were completed by physicians. One hundred seventy-six (76.8%) physicians were both allergists and immunologists. The agreement between allergists/immunologists and non-allergists/non-immunologists for the question \"Is there NBS for IEI in the country you work in?\" was good (κ = 0,64: 95% CI 0.55-0.69). Ninety-eight (42.8%) participants were from Latin America, 35 (15.3%) from North America, 29 (12.6%) from Europe, 18 (7.9%) from Africa, 44 (19.2%) from Asia, and 5 (2.2%) from Oceania. More than half the participants (n = 124, 54.2%) regularly treated patients with IEI, followed by occasional treatment (n = 77, 33.6%), or never (n = 28, 12.2%). Of the respondents, 14.8% reported that their countries performed NBS for IEI, whereas 42.2% reported their countries did not. T-cell receptor excision circles was the most widely used technique in some countries, with 75 (59.9%) for the diagnosis of NBS for IEI, followed by combined use with kappa deleting-recombination excision circles. Only 13 participants (10.3%) underwent neonatal exon screening in their respective countries. Financial and technical issues were among the major obstacles to the implementation of NBS for IEI.
UNASSIGNED: This pilot study showed that few countries have implemented NBS for IEI, despite the presence of immunology referral centers and the availability of hematopoietic stem cell transplantation and intravenous immunoglobulin replacement therapy. The findings highlight the difficulties, mainly financial and technical, hindering wide application of NBS. Sharing experiences, technologies, and resources at the international level can help overcome these difficulties.