Long-term follow-up of 168 patients with X-linked agammaglobulinemia reveals increased morbidity and mortality

The dilemma of X-linked agammaglobulinemia carriers

Background

Many patients with X-linked agammaglobulinemia (XLA) nowadays have reached adulthood, as well as their sisters, possibly carriers of a deleterious Bruton tyrosine kinase variant. Studies on motherhood outcomes in families with XLA are lacking.

Objective

We sought to investigate adherence to carrier status screening, interest in preconception and prenatal genetic counseling, and reproductive decisions in relatives with XLA.

Methods

In this multicenter, retrospective cohort study, we collected a 3-generation pedigree and data on mothers and sisters of patients with XLA, including carrier status and pregnancy outcome.

Results

Data on 53 adults with XLA, 52 mothers, and 33 sisters were collected. All XLA sisters received genetic counseling. Forty percent of the sisters chose to undergo carrier status determination, and 60% of them chose invasive prenatal testing. The main reasons for the sisters to decide not to undergo genetic testing were their young age and the willingness to carry on with the pregnancy regardless of the outcome of the genetic test, followed by the willingness to postpone the decision at the time of pregnancy and the decision to not have children. Prenatal testing resulted in 5 XLA diagnoses, with 2 pregnancy terminations, 1 miscarriage, and 2 XLA live births. Three carriers refused prenatal testing and had 6 live births, including 3 XLA-affected sons. One sister was diagnosed as a carrier after the birth of an XLA-affected son. In total, 9 XLA diagnoses were made, including 6 live births.

Conclusions

A number of XLA sister carriers decided to carry on with their pregnancy after receiving the diagnosis of an affected fetus or after refusing prenatal testing. We propose to initiate a more extensive collaborative study to verify the effect of genetic counseling on families with XLA in other cohorts from different countries.

Gut microbial dysbiosis, IgA, and Enterococcus in common variable immunodeficiency with immune dysregulation

BACKGROUND

Common variable immunodeficiency (CVID) is characterized by hypogammaglobulinemia and recurrent infections. Significant morbidity and mortality are caused by immune dysregulation complications (CVIDid), which affect around one-third of CVID patients and have a poorly understood etiology. Here, we investigate the hypothesis that gut microbial dysbiosis contributes to the inflammation underlying CVIDid.

RESULTS

Bacterial invasion of colonic crypts was observed in CVID (3/15) and X-linked agammaglobulinemia (XLA, 1/3), but not in healthy control (HC, 0/9) biopsies. Fecal gut microbiota was characterized using 16S rRNA-targeted amplicon sequencing. Increased bacterial load, decreased alpha diversity and distinct beta diversity were observed in CVIDid (n = 42) compared to HC (n = 48), and similar results were seen in CVID with IgA deficiency (n = 40) compared to HC. CVIDid and CVID-IgA showed enrichment of the genus Enterococcus, and in vitro studies confirmed the inflammatory potential of Enterococcus gallinarum and Enterococcus hirae in patient monocytes.

CONCLUSIONS

This study further supports the hypothesis that a dysregulated gut microbiota, with IgA deficiency as an important driving factor, contributes to systemic inflammation in primary antibody deficiency, and introduces enterococci as potential pathobionts in CVIDid. Video Abstract.

Evaluation and treatment of rhinosinusitis with primary antibody deficiency in children: Evidence-based review with recommendations

BACKGROUND

There is clear evidence that prevalence of primary antibody deficiency (PAD) is higher in children with chronic rhinosinusitis (CRS) than in the general population. The purpose of this multi-institutional and multidisciplinary evidence-based review with recommendations (EBRR) is to thoroughly review the literature on rhinosinusitis with PAD, summarize the existing evidence, and provide recommendations on the evaluation and management of rhinosinusitis in children with PAD.

METHODS

The PubMed, Embase, and Cochrane databases were systematically reviewed from inception through December 2023. Studies on the evaluation and management of rhinosinusitis in PAD patients were included. An iterative review process was utilized in accordance with EBRR guidelines. Levels of evidence and recommendations on the evaluation and management principles for PAD were generated.

RESULTS

A total of 50 studies were included in this evidence-based review. These studies were evaluated on the incidence of PAD in rhinosinusitis patients, the incidence of rhinosinusitis in PAD patients, and on the different treatment modalities used and their outcome. The aggregate quality of evidence varied across the reviewed domains.

CONCLUSION

Based on the currently available evidence, the incidence of PAD in children with recalcitrant CRS can be significantly elevated. Despite the presence of multiple studies addressing rhinosinusitis and PAD, the level of evidence supporting different treatment options continues to be lacking. Optimal management requires a multidisciplinary approach through collaboration with clinical immunology. There is need for higher level studies that compare different treatments in children with PAD and rhinosinusitis.

Case report of renal manifestations in X-linked agammaglobulinemia

Introduction

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.

Case description

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.

Conclusion

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.

Monogenic Inborn Errors of Immunity with impaired IgG response to polysaccharide antigens but normal IgG levels and normal IgG response to protein antigens

In patients with severe and recurrent infections, minimal diagnostic workup to test for Inborn Errors of Immunity (IEI) includes a full blood count, IgG, IgA and IgM. Vaccine antibodies against tetanus toxoid are also frequently measured, whereas testing for anti-polysaccharide IgG antibodies and IgG subclasses is not routinely performed by primary care physicians. This basic approach may cause a significant delay in diagnosing monogenic IEI that can present with an impaired IgG response to polysaccharide antigens with or without IgG subclass deficiency at an early stage. Our article reviews genetically defined IEI, that may initially present with an impaired IgG response to polysaccharide antigens, but normal or only slightly decreased IgG levels and normal responses to protein or conjugate vaccine antigens. We summarize clinical, genetic, and immunological findings characteristic for these IEI. This review may help clinicians to identify patients that require extended immunologic and genetic evaluations despite unremarkable basic immunologic findings. We recommend the inclusion of anti-polysaccharide IgG antibodies as part of the initial routine work-up for possible IEI.

Interstitial lung diseases in inborn errors of immunity

PURPOSE OF REVIEW

Our goal is to review current understanding of interstitial lung disease (ILD) affecting patients with inborn errors of immunity (IEI). This includes understanding how IEI might predispose to and promote development or progression of ILD as well as how our growing understanding of IEI can help shape treatment of ILD in these patients. Additionally, by examining current knowledge of ILD in IEI, we hope to identify key knowledge gaps that can become focus of future investigative efforts.

RECENT FINDINGS

Recent identification of novel IEI associated with ILD and the latest reports examining treatment of ILD in IEI are included. Of noted interest, are recent clinical studies of immunomodulatory therapy for ILD in common variable immunodeficiency.

SUMMARY

ILD is a frequent complication found in many IEI. This article provides a guide to identifying manifestations of ILD in IEI. We review a broad spectrum of IEI that develop ILD, including antibody deficiency and immune dysregulation disorders that promote autoimmunity and autoinflammation. This work integrates clinical information with molecular mechanisms of disease and diagnostic assessments to provide an expedient overview of a clinically relevant and expanding topic.

An International Survey of Allogeneic Hematopoietic Cell Transplantation for X-Linked Agammaglobulinemia

PURPOSE

X-linked agammaglobulinemia (XLA) is an inborn error of immunity caused by variants in Bruton's tyrosine kinase (BTK). XLA patients require lifelong immunoglobulin replacement therapy (IgRT). Only few XLA patients are indicated for allogeneic hematopoietic cell transplantation (HCT) because of severe complications. Accordingly, the published transplantation experience in XLA is minimal. We aimed to collect clinical data of XLA patients who received HCT in an international framework and to establish appropriate transplantation criteria and methods for XLA patients.

METHODS

XLA patients were recruited through a questionnaire and a literature review. The data are on patient characteristics and transplantation methods and outcomes.

RESULTS

In this study, twenty-two XLA patients who underwent HCT were recruited. The indication for HCT was recurrent or life-threatening infection in sixteen patients, malignancy in three, and other factors in three. A myeloablative conditioning, reduced toxicity myeloablative conditioning (RT-MAC), and reduced intensity conditioning (RIC) were selected in four, ten, and eight patients, respectively. Engraftment was achieved in 21 patients (95%). In all patients, 2-year overall survival (OS) and event-free survival (EFS) were 86% and 77%, respectively. In patients who received RT-MAC or RIC using treosulfan, busulfan, or melphalan, 2-year OS and EFS were 82% and 71%, respectively. Finally, twenty-one patients (95%) obtained complete or stable high-level mixed chimerism (50-95%), and the 1-year discontinuation rate of IgRT was 89%.

CONCLUSION

Based on the concept in which IgRT is the standard treatment for XLA, HCT may be an effective and safe alternative treatment option for XLA patients, and IgRT can be discontinued following transplantation. It is ideal to perform HCT in XLA patients for whom transplantation is indicated before they develop organ damage.

Investigation of a synonymous mutation in Btk in a patient with agammaglobulinemia: A case report

BACKGROUND

X-linked agammaglobulinemia (XLA) is the most common form of agammaglobulinemia and is caused by mutations in Btk, which encodes Bruton tyrosine kinase (BTK).

CASE DESCRIPTION

We describe a 36-year-old male who presented as an infant with hypogammaglobulinemia and sinopulmonary infections and was initially diagnosed with common variable immunodeficiency. Genetic testing showed he was hemizygous for Btk c.240G > A. This synonymous variant affecting the last nucleotide of exon 3 leads to aberrant splicing of most but not all mRNA transcripts.

CONCLUSION

We demonstrated reduced BTK protein expression confirming the pathogenicity of the variant and related our findings to genotype-phenotype relationship studies ina XLA caused by synonymous mutations.

Clinical features and mutational analysis of X-linked agammaglobulinemia patients in Malaysia

Background

Bruton's tyrosine kinase (BTK) is a cytoplasmic protein involved in the B cell development. X-linked agammaglobulinemia (XLA) is caused by mutation in the BTK gene, which results in very low or absent B cells. Affected males have markedly reduced immunoglobulin levels, which render them susceptible to recurrent and severe bacterial infections. Methods: Patients suspected with X-linked agammaglobulinemia were enrolled during the period of 2010-2018. Clinical summary, and immunological profiles of these patients were recorded. Peripheral blood samples were collected for monocyte BTK protein expression detection and BTK genetic analysis. The medical records between January 2020 and June 2023 were reviewed to investigate COVID-19 in XLA.

Results

Twenty-two patients (from 16 unrelated families) were molecularly diagnosed as XLA. Genetic testing revealed fifteen distinct mutations, including four splicing mutations, four missense mutations, three nonsense mutations, three short deletions, and one large indel mutation. These mutations scattered throughout the BTK gene and mostly affected the kinase domain. All mutations including five novel mutations were predicted to be pathogenic or deleterious by in silico prediction tools. Genetic testing confirmed that eleven mothers and seven sisters were carriers for the disease, while three mutations were de novo. Flow cytometric analysis showed that thirteen patients had minimal BTK expression (0-15%) while eight patients had reduced BTK expression (16-64%). One patient was not tested for monocyte BTK expression due to insufficient sample. Pneumonia (n=13) was the most common manifestation, while Pseudomonas aeruginosa was the most frequently isolated pathogen from the patients (n=4). Mild or asymptomatic COVID-19 was reported in four patients.

Conclusion

This report provides the first overview of demographic, clinical, immunological and genetic data of XLA in Malaysia. The combination of flow cytometric assessment and BTK genetic analysis provides a definitive diagnosis for XLA patients, especially with atypical clinical presentation. In addition, it may also allow carrier detection and assist in genetic counselling and prenatal diagnosis.

A Registry Study of 240 Patients with X-Linked Agammaglobulinemia Living in the USA

PURPOSE

To understand the natural history and clinical outcomes for patients with X-linked agammaglobulinemia (XLA) in the United States utilizing the United States Immunodeficiency Network (USIDNET) patient registry.

METHODS

The USIDNET registry was queried for data from XLA patients collected from 1981 to 2019. Data fields included demographics, clinical features before and after diagnosis of XLA, family history, genetic mutation in Bruton's tyrosine kinase (BTK), laboratory findings, treatment modalities, and mortality.

RESULTS

Data compiled through the USIDNET registry on 240 patients were analyzed. Patient year of birth ranged from 1945 to 2017. Living status was available for 178 patients; 158/178 (88.8%) were alive. Race was reported for 204 patients as follows: White, 148 (72.5%); Black/African American, 23 (11.2%); Hispanic, 20 (9.8%); Asian or Pacific Islander, 6 (2.9%), and other or more than one race, 7 (3.4%). The median age at last entry, age at disease onset, age at diagnosis, and length of time with XLA diagnosis was 15 [range (r) = 1-52 years], 0.8 [r = birth-22.3 years], 2 [r = birth-29 years], and 10 [r = 1-56 years] years respectively. One hundred and forty-one patients (58.7%) were < 18 years of age. Two hundred and twenty-one (92%) patients were receiving IgG replacement (IgGR), 58 (24%) were on prophylactic antibiotics, and 19 (7.9%) were on immunomodulatory drugs. Eighty-six (35.9%) patients had undergone surgical procedures, two had undergone hematopoietic cell transplantation, and two required liver transplantation. The respiratory tract was the most affected organ system (51.2% of patients) followed by gastrointestinal (40%), neurological (35.4%), and musculoskeletal (28.3%). Infections were common both before and after diagnosis, despite IgGR therapy. Bacteremia/sepsis and meningitis were reported more frequently before XLA diagnosis while encephalitis was more commonly reported after diagnosis. Twenty patients had died (11.2%). The median age of death was 21 years (range = 3-56.7 years). Neurologic condition was the most common underlying co-morbidity for those XLA patients who died.

CONCLUSIONS

Current therapies for XLA patients reduce early mortality, but patients continue to experience complications that impact organ function. With improved life expectancy, more efforts will be required to improve post-diagnosis organ dysfunction and quality of life. Neurologic manifestations are an important co-morbidity associated with mortality and not yet clearly fully understood.

Gastrointestinal Involvement in Primary Antibody Deficiencies

Primary antibody deficiencies (PADs) are the most frequent group of inborn errors of immunity. Impaired B-cell development, reduced production of immunoglobulins (mainly IgG and IgA), and specific antibodies resulting in recurrent infections are their hallmarks. Infections typically affect the respiratory tract; however, gastrointestinal involvement is also common. These include infection with Helicobacter pylori, Salmonella, Campylobacter species, Giardia, and noroviruses. Impaired IgA production also contributes to dysbiosis and thereby an increase in abundance of species with proinflammatory properties, resulting in immune system dysregulation. Dysregulation of the immune system results in a broad spectrum of non-infectious manifestations, including autoimmune, lymphoproliferative, and granulomatous complications. Additionally, it increases the risk of malignancy, which may be present in more than half of patients with PADs. Higher prevalence is often seen in monogenic causes, and gastrointestinal involvement may clinically mimic various conditions including inflammatory bowel diseases and celiac disease but possess different immunological features and response to standard treatment, which make diagnosis and therapy challenging. The spectrum of malignancies includes gastric cancer and lymphoma. Thus, non-infectious manifestations significantly affect mortality and morbidity. In this overview, we provide a comprehensive insight into the epidemiology, genetic background, pathophysiology, and clinical manifestations of infectious and non-infectious complications.

Systematic errors in annotations of truncations, loss-of-function and synonymous variants

Description of genetic phenomena and variations requires exact language and concepts. Vast amounts of variation data are produced with next-generation sequencing pipelines. The obtained variations are automatically annotated, e.g., for their functional consequences. These tools and pipelines, along with systematic nomenclature, mainly work well, but there are still some problems in nomenclature, organization of some databases, misuse of concepts and certain practices. Therefore, systematic errors prevent correct annotation and often preclude further analysis of certain variation types. Problems and solutions are described for presumed protein truncations, variants that are claimed to be of loss-of-function based on the type of variation, and synonymous variants that are not synonymous and lead to sequence changes or to missing protein.

X-Linked Agammaglobulinemia Leading to Chronic Obstructive Lung Disease

X-linked agammaglobulinemia (XLA) is a rare primary immunodeficiency disorder. It occurs in around one in 200,000 live births and is caused by mutations in the Bruton Tyrosine Kinase (BTK) gene leading to B lymphocyte deficiency and increased susceptibility to infection. Infection is the most common initial clinical presentation, followed by family history and neutropenia. Even in patients with a positive family history, only 34% of patients were diagnosed before clinical symptoms arose. Over half of patients are diagnosed by two years of age. Treatment is aimed at replacing immunoglobulin using intravenous immunoglobulin (IVIG) or subcutaneous immunoglobulin (SCIG) and prophylactic antibiotics to prevent infections. Despite these therapies, patients still suffer from repetitive infections. Another significant source of morbidity in patients with XLA is a chronic lung disease. By the time of diagnosis, 62% of patients had at least one case of pneumonia. We describe the case of a patient who has developed an accelerated course of chronic obstructive pulmonary disease (COPD) secondary to pre-existing X-linked agammaglobulinemia and recurrent respiratory infections.

Bronchiectasis and obstructive lung diseases in primary antibody deficiencies and beyond: update on management and pathomechanisms

PURPOSE OF REVIEW

Pulmonary complications are among the most frequent manifestations in patients with primary antibody deficiency (PAD), contributing significantly to morbidity and mortality. Here, we focus on recent findings in obstructive pulmonary disease and bronchiectasis in PAD. Since specific data on patients with PAD is limited and management mostly follows general recommendations, this review also aims to summarize data from the immunocompetent population.

RECENT FINDINGS

Potential risk factors for the development and progression of bronchiectasis include reduced immunoglobulins and lower CD4 cells. In addition, Pseudomonas aeruginosa and an altered microbiome might contribute to local inflammation and disease progression. Findings on the contribution of neutrophils and eosinophils in the affected immunocompetent population require confirmation in PAD. Despite its high global burden, there is an extreme paucity of data on chronic obstructive pulmonary disease in PAD. Lower IgA and IgM are associated with asthma in PAD, but the heterogeneity of prevalence among PAD groups is poorly understood. Recent observations of non-IgE-mediated pathomechanisms in asthma may be of particular interest in PAD patients.

SUMMARY

Management of PAD patients with chronic lung disease requires a multidisciplinary team approach including immunology, pulmonology, infectious disease and physiotherapy. Diagnostic processes should be harmonized to ensure a more precise perspective on prevalence and disease courses.

Clinical Aspects of B Cell Immunodeficiencies: The Past, the Present and the Future

B cells and antibodies are indispensable for host immunity. Our understanding of the mechanistic processes that underpin how B cells operate has left an indelible mark on the field of clinical pathology, and recently has also dramatically reshaped the therapeutic landscape of diseases that were once considered incurable. Evaluating patients with primary immunodeficiency diseases (PID)/inborn errors of immunity (IEI) that primarily affect B cells, offers us an opportunity to further our understanding of how B cells develop, mature, function and, in certain instances, cause further disease. In this review we provide a brief compendium of IEI that principally affect B cells at defined stages of their developmental pathway, and also attempt to offer some educated viewpoints on how the management of these disorders could evolve over the years.

Atopic Dermatitis-like Genodermatosis: Disease Diagnosis and Management

Eczema is a classical characteristic not only in atopic dermatitis but also in various genodermatosis. Patients suffering from primary immunodeficiency diseases such as hyper-immunoglobulin E syndromes, Wiskott-Aldrich syndrome, immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome, STAT5B deficiency, Omenn syndrome, atypical complete DiGeorge syndrome; metabolic disorders such as acrodermatitis enteropathy, multiple carboxylase deficiency, prolidase deficiency; and other rare syndromes like severe dermatitis, multiple allergies and metabolic wasting syndrome, Netherton syndrome, and peeling skin syndrome frequently perform with eczema-like lesions. These genodermatosis may be misguided in the context of eczematous phenotype. Misdiagnosis of severe disorders unavoidably affects appropriate treatment and leads to irreversible outcomes for patients, which underlines the importance of molecular diagnosis and genetic analysis. Here we conclude clinical manifestations, molecular mechanism, diagnosis and management of several eczema-related genodermatosis and provide accessible advice to physicians.

Genes as Medicine: The Development of Gene Therapies for Inborn Errors of Immunity

The field of gene therapy has experienced tremendous growth in the last decade ranging from improvements in the design of viral vectors for gene addition of therapeutic gene cassettes to the discovery of site-specific nucleases targeting transgenes to desired locations in the genome. Such advancements have not only enabled the development of disease models but also created opportunities for the development of tailored therapeutic approaches. There are 3 main methods of gene modification that can be used for the prevention or treatment of disease. This includes viral vector-mediated gene therapy to supply or bypass a missing/defective gene, gene editing enabled by programmable nucleases to create sequence-specific alterations in the genome, and gene silencing to reduce the expression of a gene or genes. These gene-modification platforms can be delivered either in vivo, for which the therapy is injected directed into a patient's body, or ex vivo, in which cells are harvested from a patient and modified in a laboratory setting, and then returned to the patient.

TREC/KREC Newborn Screening followed by Next-Generation Sequencing for Severe Combined Immunodeficiency in Japan

PURPOSE

The aim of this study is to evaluate the usefulness of T cell receptor excision circle (TREC) and/or kappa-deleting recombination excision circle (KREC) measurements integrated with diagnostic next-generation sequencing (NGS) analysis using a severe combined immunodeficiency (SCID) newborn screening (NBS) program.

METHODS

TREC and/or KREC values were measured in 137,484 newborns between April 2017 and December 2021 using EnLite TREC (n = 80,791) or TREC/KREC kits (n = 56,693). For newborns with positive screening results, diagnostic NGS analysis was performed with a 349-gene panel to detect genetic mutations associated with primary immunodeficiencies (PIDs).

RESULTS

A total of 145 newborns (0.11%) had abnormal TREC and/or KREC values, and a genetic diagnosis was established in 2 patients with SCID (1 in 68,742 newborns) (IL2RG-SCID and reticular dysgenesis) and 10 with non-SCID PIDs with T and/or B cell deficiencies (1 in 13,748 newborns) using NGS analysis. Furthermore, TREC values of 2849 newborns were measured and confirmed the significant correlation between the results of both TREC and TREC/KREC kits (P < 0.001) and naïve T cell counts.

CONCLUSIONS

We performed the first large-scale TREC and TREC/KREC NBS programs in Japan. Our NBS programs followed by the diagnostic NGS analysis for newborns with abnormal TREC and/or KREC values are useful for the early identification and rapid molecular evaluation of not only SCID but also different non-SCID PIDs.

X-Linked Agammaglobulinemia: Infection Frequency and Infection-Related Mortality in the USIDNET Registry

X-linked agammaglobulinemia (XLA) is a primary immunodeficiency disorder caused by mutations in the Bruton tyrosine kinase (BTK) gene leading to B lymphocyte deficiency and susceptibility to infection. A potential benefit of earlier diagnosis and treatment initiation on morbidity and mortality in XLA is incompletely understood. In the USIDNET Registry, we describe infection frequency and infection-related mortality in patients with XLA and their relationship to age of diagnosis and treatment initiation. Among the 231 XLA patients enrolled in the Registry, respiratory infections (N = 203, 88%) were the most commonly reported. Among those deceased (N = 20) where cause of death was known (N = 17), mortality was attributed to infection in most (N = 12, 71%). Chronic lung disease, often a consequence of repeated lower respiratory tract infection (LRTI), was also a frequent complication associated with mortality (N = 9, 53%). Age of diagnosis in years was lower for those without LRTI compared to those with (median 1.5 [IQR 0.5-3.3] vs. median 3.0 [IQR 1.0-5.0], p = 0.0026) and among living patients compared to deceased (median 1.8 [IQR 0.5-5.0] vs. median 2.7 [IQR 1.6-6.0], p = 0.04). Age at treatment initiation in years was lower among those without LRTIs compared to those with (median 1.0 [IQR 0.4-2.4] vs. median 2.8 [IQR 1.0-5.4], p = 0.0006). For every year increase in age at start of therapy, the odds of experiencing a LRTI was 1.216 (OR 1.216, 95% CI 1.048-1.411, p = 0.01). Given the expected finding of reduced LRTIs and mortality among those with earlier age at diagnosis, our study findings support inclusion of XLA in newborn screening programs.

The inhibitory coreceptor CD22 restores B cell signaling by developmentally regulating Cd45-/- immunodeficient B cells

The protein tyrosine phosphatase CD45 plays a crucial role in B cell antigen receptor (BCR) signaling by activating Src family kinases. Cd45^-/- mice show altered B cell development and a phenotype likely due to reduced steady-state signaling; however, Cd45^-/- B cells show relatively normal BCR ligation-induced signaling. In our investigation of how BCR signaling was restored in Cd45^-/- cells, we found that the coreceptor CD22 switched from an inhibitory to a stimulatory function in these cells. We disrupted the ability of CD22 to interact with its ligands in Cd45^-/- B cells by generating Cd45^-/-St6galI^-/- mice, which cannot synthesize the glycan ligand of CD22, or by treating Cd45^-/- B cells in vitro with the sialoside GSC718, which inhibits ligand binding to CD22. BCR ligation-induced signaling was reduced by ST6GalI deficiency, but not by GSC718 treatment, suggesting that CD22 restored BCR ligation-induced signaling in Cd45^-/- mature B cells by altering cellular phenotypes during development. CD22 was required for the increase in the surface amount of IgM-BCR on Cd45^-/- B cells, which augmented signaling. Because B cell survival depends on steady-state BCR signaling, IgM-BCR abundance was likely increased by the selective survival of IgM-BCR^hi Cd45^-/- B cells because of CD22-mediated signaling under conditions of substantially reduced steady-state signaling. Because the amount of surface IgM-BCR is increased on B cells from patients with other BCR signaling deficiencies, including X-linked agammaglobulinemia, our findings suggest that CD22 may contribute to the partial restoration of B cell function in these patients.

Respiratory Infections in Patients with Primary Immunodeficiency

Recurrent and life-threatening respiratory infections are nearly universal in patients with primary immunodeficiency diseases (PIDD). Early recognition, aggressive treatment, and prophylaxis with antimicrobials and immunoglobulin replacement have been the mainstays of management and will be reviewed here with an emphasis on respiratory infections. Genetic discoveries have allowed direct translation of research to clinical practice, improving our understanding of clinical patterns of pathogen susceptibilities and guiding prophylaxis. The recent identification of inborn errors in type I interferon signaling as a basis for life-threatening viral infections in otherwise healthy individuals suggests another targetable pathway for treatment and/or prophylaxis. The future of PIDD diagnosis will certainly involve early genetic identification by newborn screening before onset of infections, with early treatment offering the potential of preventing disease complications such as chronic lung changes. Gene editing approaches offer tremendous therapeutic potential, with rapidly emerging delivery systems. Antiviral therapies are desperately needed, and specific cellular therapies show promise in patients requiring hematopoietic stem cell transplantation. The introduction of approved therapies for clinical use in PIDD is limited by the difficulty of studying outcomes in rare patients/conditions with conventional clinical trials.

Identification of four novel mutations in BTK from six Chinese families with X-linked agammaglobulinemia

BACKGROUND

The defect of Bruton's tyrosine kinase (BTK) gene resulted in X-linked agammaglobulinemia (XLA), which is characterized by recurrent bacterial infections, immunodeficiency with low B-cell numbers and immunoglobulin. Diagnosis of XLA depends on clinical phenotype and genetic testing.

METHODS

Six unrelated Chinese families with high suspicion of XLA were enrolled in this study. Potential pathogenic variants were detected and validated by Whole Exome Sequencing (WES) and Sanger Sequencing. Western blot, Quantitative PCR (qPCR) analysis and immunofluorescence analysis were used to evaluate the preliminary function of candidate BTK variants.

RESULTS

A total of six variants were identified, four of which were not reported before. The novel missense mutation(c.1900T>G) and deletion(c.897delG) were found that the mutant protein and mRNA expression levels have fallen by Western Blot and qPCR identification. We also constructed minigene expression vector to determine the deletion (c.1751-6_1755delttctagGGGTT) resulting a 35bp skipping in exon 18. Meanwhile, the break point of gross deletion (Exon2-5) discovered based on WES was confirmed to be located at site ChX:101367539_101376531 through qPCR and Gap-PCR.

CONCLUSION

This study makes definitive diagnosis for 6 families with suspected XLA and further expands the spectrum of BTK mutations, providing new information for the diagnosis of the disease.

Cost Utility of Lifelong Immunoglobulin Replacement Therapy vs Hematopoietic Stem Cell Transplant to Treat Agammaglobulinemia

IMPORTANCE

Lifelong immunoglobulin replacement therapy (IRT) is standard-of-care treatment for congenital agammaglobulinemia but accrues high annual costs ($30 000-$90 000 per year) and decrements to quality of life over patients' life spans. Hematopoietic stem cell transplant (HSCT) offers an alternative 1-time therapy, but has high morbidity and mortality.

OBJECTIVE

To evaluate the cost utility of IRT vs matched sibling donor (MSD) and matched unrelated donor (MUD) HSCT to treat patients with agammaglobulinemia in the US.

DESIGN, SETTING, AND PARTICIPANTS

This economic evaluation used Markov analysis to model the base-case scenario of a patient aged 12 months with congenital agammaglobulinemia receiving lifelong IRT vs MSD or MUD HSCT. Costs, probabilities, and quality-of-life measures were derived from the literature. Microsimulations estimated premature deaths for each strategy in a virtual cohort. One-way sensitivity and probabilistic sensitivity analyses evaluated uncertainty around parameter estimates performed from a societal perspective over a 100-year time horizon. The threshold for cost-effective care was set at $100 000 per quality-adjusted life-year (QALY). This study was conducted from 2020 across a 100-year time horizon.

EXPOSURES

Immunoglobulin replacement therapy vs MSD or MUD HSCT for treatment of congenital agammaglobulinemia.

MAIN OUTCOMES AND MEASURES

The primary outcomes were incremental cost-effectiveness ratio (ICER) expressed in 2020 US dollars per QALY gained and premature deaths associated with each strategy.

RESULTS

In this economic evaluation of patients with congenital agammaglobulinemia, lifelong IRT cost more than HSCT ($1 512 946 compared with $563 776 [MSD] and $637 036 [MUD]) and generated similar QALYs (20.61 vs 17.25 [MSD] and 17.18 [MUD]). Choosing IRT over MSD or MUD HSCT yielded ICERs of $282 166 per QALY gained over MSD and $255 633 per QALY gained over MUD HSCT, exceeding the US willingness-to-pay threshold of $100 000/QALY. However, IRT prevented at least 2488 premature deaths per 10 000 microsimulations compared with HSCT. When annual IRT price was reduced from $60 145 to below $29 469, IRT became the cost-effective strategy. Findings remained robust in sensitivity and probabilistic sensitivity analyses.

CONCLUSIONS AND RELEVANCE

In the US, IRT is more expensive than HSCT for agammaglobulinemia treatment. The findings of this study suggest that IRT prevents more premature deaths but does not substantially increase quality of life relative to HSCT. Reducing US IRT cost by 51% to a value similar to IRT prices in countries implementing value-based pricing may render it the more cost-effective strategy.

B cell repertoire in patients with a novel BTK mutation: expanding the spectrum of atypical X-linked agammaglobulinemia

X-linked agammaglobulinemia (XLA) is caused by mutations in the Bruton tyrosine kinase) BTK) gene. Affected patients have severely reduced amounts of circulating B cells. Patients with atypical XLA may have residual circulating B cells, and there are few studies exploring these cells' repertoire. We aimed to study the B cell repertoire of a novel hypomorphic mutation in the BTK gene, using the next generation sequencing (NGS) technology. Clinical data was collected from our clinical records. Real-time PCR was used to determine KREC copies, and NGS was used to determine the immunoglobulin (Ig) heavy chain (IgH) repertoire diversity. Both patients had a relatively mild clinical and laboratory phenotype, residual BTK protein expression, and the same novel mutation in the BTK gene, c.1841 T > C, p. L614P. Signal-joint kappa-deleting recombination excision circles (sj-KREC) for both patients were completely absent reflecting lack of naïve B cells. The intron RSS-Kde coding joints (cj) were significantly reduced, reflecting residual replicating B cells. NGS displayed restricted IgH repertoire with highly uneven distribution of clones, especially for Pt2. We report a novel BTK mutation, c.1841 T > C (p. L614P) that is associated with a relatively mild phenotype. We conclude that the IgH repertoire in atypical XLA is restricted with highly uneven distribution of clones. This phenomenon may be explained by extremely reduced to non-existent levels of BTK in B cells. This report sheds further light on atypical cases of XLA.

Agammaglobulinemia: from X-linked to Autosomal Forms of Disease

Interruptions or alterations in the B cell development pathway can lead to primary B cell immunodeficiency with resultant absence or diminished immunoglobulin production. While the most common cause of congenital agammaglobulinemia is X-linked agammaglobulinemia (XLA), accounting for approximately 85% of cases, other genetic forms of agammaglobulinemia have been identified. Early recognition and diagnosis of these conditions are pivotal for improved outcomes and prevention of sequelae and complications. The diagnosis of XLA is often delayed, and can be missed if patient has a mild phenotype. The lack of correlation between phenotype and genotype in this condition makes management and predicting outcomes quite difficult. In contrast, while less common, autosomal recessive forms of agammaglobulinemia present at younger ages and with typically more severe clinical features resulting in an earlier diagnosis. Some diagnostic innovations, such as KREC level measurements and serum BCMA measurements, may aid in facilitating an earlier identification of agammaglobulinemia leading to prompt treatment. Earlier diagnosis may improve the overall health of patients with XLA.

Nodular regenerative hyperplasia in X-linked agammaglobulinemia: An underestimated and severe complication

BACKGROUND

Late-onset complications in X-linked agammaglobulinemia (XLA) are increasingly recognized. Nodular regenerative hyperplasia (NRH) has been reported in primary immunodeficiency but data in XLA are limited.

OBJECTIVES

This study sought to describe NRH prevalence, associated features, and impact in patients with XLA.

METHODS

Medical records of all patients with XLA referred to the National Institutes of Health between October 1994 and June 2019 were reviewed. Liver biopsies were performed when clinically indicated. Patients were stratified into NRH+ or NRH- groups, according to their NRH biopsy status. Fisher exact test and Mann-Whitney test were used for statistical comparisons.

RESULTS

Records of 21 patients with XLA were reviewed, with a cumulative follow-up of 129 patient-years. Eight patients underwent ≥1 liver biopsy of whom 6 (29% of the National Institutes of Health XLA cohort) were NRH+. The median age at NRH diagnosis was 20 years (range, 17-31). Among patients who had liver biopsies, alkaline phosphatase levels were only increased in patients who were NRH+ (P = .04). Persistently low platelet count (<100,000 per μL for >6 months), mildly to highly elevated hepatic venous pressure gradient and either hepatomegaly and/or splenomegaly were present in all patients who were NRH+. In opposition, persistently low platelet counts were not seen in patients who were NRH-, and hepatosplenomegaly was observed in only 1 patient who was NRH-. Hepatic venous pressure gradient was normal in the only patient tested who was NRH-. All-cause mortality was higher among patients who were NRH+ (5 of 6, 83%) than in the rest of the cohort (1 of 15, 7% among patients who were NRH- and who were classified as unknown; P = .002).

CONCLUSIONS

NRH is an underreported, frequent, and severe complication in XLA, which is associated with increased morbidity and mortality.

SARS-CoV-2 Vaccine Induced Atypical Immune Responses in Antibody Defects: Everybody Does their Best

Background

Data on immune responses to SARS-CoV-2 in patients with Primary Antibody Deficiencies (PAD) are limited to infected patients and to heterogeneous cohorts after immunization.

Methods

Forty-one patients with Common Variable Immune Deficiencies (CVID), six patients with X-linked Agammaglobulinemia (XLA), and 28 healthy age-matched controls (HD) were analyzed for anti-Spike and anti-receptor binding domain (RBD) antibody production, generation of Spike-specific memory B-cells, and Spike-specific T-cells before vaccination and one week after the second dose of BNT162b2 vaccine.

Results

The vaccine induced Spike-specific IgG and IgA antibody responses in all HD and in 20% of SARS-CoV-2 naive CVID patients. Anti-Spike IgG were detectable before vaccination in 4 out 7 CVID previously infected with SARS-CoV-2 and were boosted in six out of seven patients by the subsequent immunization raising higher levels than patients naïve to infection. While HD generated Spike-specific memory B-cells, and RBD-specific B-cells, CVID generated Spike-specific atypical B-cells, while RBD-specific B-cells were undetectable in all patients, indicating the incapability to generate this new specificity. Specific T-cell responses were evident in all HD and defective in 30% of CVID. All but one patient with XLA responded by specific T-cell only.

Conclusion

In PAD patients, early atypical immune responses after BNT162b2 immunization occurred, possibly by extra-follicular or incomplete germinal center reactions. If these responses to vaccination might result in a partial protection from infection or reinfection is now unknown. Our data suggests that SARS-CoV-2 infection more effectively primes the immune response than the immunization alone, possibly suggesting the need for a third vaccine dose for patients not previously infected.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10875-021-01133-0.

Inborn errors of immunity: Recent progress

Recent advances in the field of inborn errors of immunity (IEIs) have been wide in scope, including progress in mechanisms of disease, diagnosis, and management. New gene defects affecting the immune response continue to be reported, as many as 26 in the year 2020. It was noted that the presentation of IEIs might not include recurrent infections in 9% of cases, and that current diagnostic methods can identify molecular causes in 92% of patients with severe combined immunodeficiency. Progress in immunopathogenesis explained mechanisms leading to symptoms of autosomal-recessive hyper-IgE syndrome. There was an emphasis on research in primary antibody deficiencies. The benefit of antibiotic prophylaxis to reduce the frequency of infections was demonstrated in these patients. The regimen of rituximab and azathioprine or mycophenolate was proven effective for chronic granulocytic interstitial pneumonia. The efficacy and adverse events of hematopoietic stem cell transplant in different IEI conditions were reported, as well as different strategies to improve outcomes, supporting its use in immunodeficiency and immunodysregulatory syndromes. The recent pandemic of coronavirus disease 2019 affected patients with IEIs, in particular those with deficiency in the interferon-mediated activation of the immune response. Initial data suggest that coronavirus disease 2019 vaccines might elicit anti-coronavirus disease 2019-neutralizing antibody responses in some patients with IEI conditions.

Peripheral B Cell Deficiency and Predisposition to Viral Infections: The Paradigm of Immune Deficiencies

In the era of COVID-19, understanding how our immune system responds to viral infections is more pertinent than ever. Immunodeficiencies with very low or absent B cells offer a valuable model to study the role of humoral immunity against these types of infection. This review looks at the available evidence on viral infections in patients with B cell alymphocytosis, in particular those with X-linked agammaglobulinemia (XLA), Good’s syndrome, post monoclonal-antibody therapy and certain patients with Common Variable Immune Deficiency (CVID). Viral infections are not as infrequent as previously thought in these conditions and individuals with very low circulating B cells seem to be predisposed to an adverse outcome. Particularly in the case of SARS-CoV2 infection, mounting evidence suggests that peripheral B cell alymphocytosis is linked to a poor prognosis.

Haematopoietic Stem Cell Transplant for Norovirus-Induced Intestinal Failure in X-linked Agammaglobulinemia

Since the first clinical description in 1952, immunoglobulin replacement therapy remains the mainstay of treatment of patients with X-linked agammaglobulinemia (XLA). However, this therapy only replaces IgG isotype and does not compensate for the loss of Bruton tyrosine kinase in non-B-lymphocytes. Patients may still therefore develop complications despite current standard of care. Here, we describe an XLA patient with persistent chronic norovirus infection, refractory to treatment and causing intestinal failure. The patient underwent haematopoietic stem cell transplantation, curing XLA and allowed clearance of norovirus prior to humoral immunoreconstitution, suggesting non-humoral immunodeficiency in these patients.

The New "Wholly Trinity" in the Diagnosis and Management of Inborn Errors of Immunity

The field of immunology has a rich and diverse history, and the study of inborn errors of immunity (IEIs) represents both the "cake" and the "icing on top of the cake," as it has enabled significant advances in our understanding of the human immune system. This explosion of knowledge has been facilitated by a unique partnership, a triumvirate formed by the physician who gathers detailed immunological and clinical phenotypic information from, and shares results with, the patient; the laboratory scientist/immunologist who performs diagnostic testing, as well as advanced functional correlative studies; and the genomics scientist/genetic counselor, who conducts and interprets varied genetic analyses, all of which are essential for dissecting constitutional genetic disorders. Although the basic principles of clinical care have not changed in recent years, the practice of clinical immunology has changed to reflect the prodigious advances in diagnostics, genomics, and therapeutics. An "omic/tics"-centric approach to IEI reflects the tremendous strides made in the field in the new millennium with recognition of new disorders, characterization of the molecular underpinnings, and development and implementation of personalized treatment strategies. This review brings renewed attention to bear on the indispensable "trinity" of phenotypic, genomic, and immunological analyses in the diagnosis, management, and treatment of IEIs.

Crohn's-like Enteritis in X-Linked Agammaglobulinemia: A Case Series and Systematic Review

BACKGROUND

X-linked agammaglobulinemia (XLA) is an inherited primary immunodeficiency that usually manifests clinically with recurrent sinopulmonary infections. Gastrointestinal manifestations are mostly driven by acute infections and disturbed mucosal immunity, but there is a notable prevalence of inflammatory bowel disease (IBD). Differentiating between XLA-associated enteritis, which can originate from recurrent infections, and IBD can be diagnostically and therapeutically challenging.

OBJECTIVE

This study presents a critical appraisal of the clinical, radiological, endoscopic, and histological features associated with XLA-associated Crohn disease (CD)-like enteritis.

METHODS

We report 3 cases and performed a systematic review of the literature describing the diagnoses and outcomes.

RESULTS

An XLA-related enteropathy presented in adolescence with an ileocolonic CD-like phenotype without perianal disease. Abdominal pain, noninfectious diarrhea, and weight loss were the most common symptoms. Imaging and endoscopic findings closely resemble CD. However, histologically, it presents without nodular lymphoid hyperplasia and only 2 studies reported the presence of granulomas. In addition, in XLA-associated enteritis, immunohistochemistry showed the absence or marked reduction in B cells and plasma cells.

CONCLUSIONS

An XLA-associated enteritis is a distinct pathological process that presents clinically in a manner similar to ileocolonic CD. It is important to evaluate for infectious diarrhea, which is common in XLA and can mimic IBD clinically. Complete multidisciplinary evaluation is, therefore, recommended for XLA patients with persistent gastrointestinal symptoms. Although more research is needed, therapeutic selection for XLA-associated enteritis is like that of IBD, and the possible risk of drug interactions and complications from increasing immunosuppression should be considered.

Management of patients with neuromuscular disorders at the time of the SARS-CoV-2 pandemic

The novel Coronavirus disease-19 (COVID-19) pandemic has posed several challenges for neuromuscular disorder (NMD) patients. The risk of a severe course of SARS-CoV-2 infection is increased in all but the mildest forms of NMDs. High-risk conditions include reduced airway clearance due to oropharyngeal weakness and risk of worsening with fever, fasting or infection Isolation requirements may have an impact on treatment regimens administered in hospital settings, such as nusinersen, glucosidase alfa, intravenous immunoglobulin, and rituximab infusions. In addition, specific drugs for SARS-CoV2 infection under investigation impair neuromuscular function significantly; chloroquine and azithromycin are not recommended in myasthenia gravis without available ventilatory support and prolonged prone positioning may influence options for treatment. Other therapeutics may affect specific NMDs (metabolic, mitochondrial, myotonic diseases) and experimental approaches for Coronavirus disease 2019 may be offered "compassionately" only after consulting the patient's NMD specialist. In parallel, the reorganization of hospital and outpatient services may change the management of non-infected NMD patients and their caregivers, favouring at-distance approaches. However, the literature on the validation of telehealth in this subgroup of patients is scant. Thus, as the first wave of the pandemic is progressing, clinicians and researchers should address these crucial open issues to ensure adequate caring for NMD patients. This manuscript summarizes available evidence so far and provides guidance for both general neurologists and NMD specialists dealing with NMD patients in the time of COVID-19.

Current Spectrum of Infections in Patients with X-Linked Agammaglobulinemia

Outcome of patients with X-linked agammaglobulinemia (XLA) has improved with the widespread use of immunoglobulin replacement therapy (IgRT). There are few data on the spectrum of infections experienced by patients undergoing IgRT. We carried out a retrospective cross-sectional analysis of the records of XLA patients seen at Necker-Enfants Malades Hospital, Paris. For each infection, we evaluated infection site, microbial etiology, antibiotic prophylaxis, immunosuppressive treatment, IgRT route, and last known IgG trough level. Sixty patients were included, who cumulated a follow-up of 1470 patient-years. We recorded 188 infections, including 97 after initiation of IgRT. The rate of infection was highest before IgRT (0.66 vs. 0.06 per person-year (ppy), p < 0.001) and was higher after the age of 16 compared to before (0.14 vs. 0.05 ppy, p = 0.048). It was similar for patients receiving intravenous or subcutaneous Ig (0.09 vs 0.05 ppy, p = 0.54). The lungs and gastrointestinal tract accounted for 71% of infection sites. Forty-six (47%) infections occurred in patients receiving antibiotic prophylaxis. Sixteen (16.5%) infections occurred in patients receiving immunosuppressive therapy, which more frequently occurred after age 16 (35% vs. 2.4%, p < 0.001). The median IgG trough level prior to all infections was 8.4 g/L. Almost half (44.3%) of infections occurred with prior IgG trough levels > 8 g/L, and 16/97 (16.7%) in patients with trough levels > 10 g/L. Infection remains a significant issue in patients with XLA undergoing IgRT despite adequate IgG trough levels. Chronic inflammatory manifestations of X-linked agammaglobulinemia and immunosuppressive therapies may be significant drivers of infection during adulthood.

The Use of Bruton's Tyrosine Kinase Inhibitors to Treat Allergic Disorders

Purpose of review

Studies show that inhibitors of Bruton’s tyrosine kinase (BTKis), currently FDA-approved for the treatment of B cell malignancies, can prevent IgE-mediated reactions through broad inhibition of the FcεRI signaling pathway in human mast cells and basophils. This review will summarize recent data supporting the use of these drugs as novel therapies in various allergic disorders.

Recent findings

Recent studies have shown that BTKis can prevent IgE-mediated degranulation and cytokine production in primary human mast cells and basophils. Two oral doses of the second-generation BTKi acalabrutinib can completely prevent moderate passive systemic anaphylaxis in humanized mice and even protect against death during severe anaphylaxis. Furthermore, two doses of ibrutinib can reduce or eliminate skin prick test responses to foods and aeroallergens in allergic subjects. BTKis in development also show efficacy in clinical trials for chronic urticaria. Unlike other therapies targeting IgE, such as omalizumab, BTKis appear to have rapid onset and transient effects, making them ideal candidates for intermittent use to prevent acute reactions such as IgE-mediated anaphylaxis.

Summary

These studies suggest that BTKis may be capable of preventing IgE-mediated anaphylaxis, paving the way for future trials in food allergy and urticaria.

Inborn Errors of Immunity and Cancer

Simple Summary

Inborn Errors of Immunity (IEI) are a heterogeneous group of disorders characterized by a defect in the function of at least one, and often more, components of the immune system. The overall risk for cancer in children with IEI ranges from 4 to 25%. Several factors, namely, age of the patient, viral infection status and IEI type can influence the development of different cancer types. Immunologists and oncologists should interact to monitor and promptly diagnose the potential development of cancer in known IEI patients, as well as an underlying IEI in newly diagnosed cancers with suggestive medical history or high rate of therapy-related toxicity. The creation of an international registry of IEI cases with detailed information on the occurrence of cancer is fundamental to optimizing the diagnostic process and to evaluating the outcomes of new therapeutic options, with the aim of improving prognosis and reducing comorbidities.

Abstract

Inborn Errors of Immunity (IEI) are a heterogeneous group of disorders characterized by a defect in the function of at least one, and often more, components of the immune system. The aim of this narrative review is to discuss the epidemiology, the pathogenesis and the correct management of tumours in patients with IEI. PubMed was used to search for all of the studies published over the last 20 years using the keywords: “inborn errors of immunity” or “primary immunodeficiency” and “cancer” or “tumour” or “malignancy”. Literature analysis showed that the overall risk for cancer in children with IEI ranges from 4 to 25%. Several factors, namely, age of the patient, viral infection status and IEI type can influence the development of different cancer types. The knowledge of a specific tumour risk in the presence of IEI highlights the importance of a synergistic effort by immunologists and oncologists in tracking down the potential development of cancer in known IEI patients, as well as an underlying IEI in patients with newly diagnosed cancers. In the current genomic era, the creation of an international registry of IEI cases integrated with malignancies occurrence information is fundamental to optimizing the diagnostic process and to evaluating the outcomes of new therapeutic options, with the hope to obtain a better prognosis for these patients.

Atypical Presentation of Severe Fungal Necrotizing Fasciitis in a Patient with X-Linked Agammaglobulinemia

X-linked agammaglobulinemia is a rare primary immunodeficiency due to a BTK mutation. The patients are characteristically deficient in peripheral B cells and serum immunoglobulins. While they are susceptible to infections caused by bacteria, enteroviruses, and parasites, fungal infections are uncommon in XLA patients. Here, we report a boy of Malay ethnicity who suffered from recurrent upper respiratory tract infections and severe progressive necrotizing fasciitis caused by Saksenaea erythrospora. Immunological tests showed a B cell deficiency and hypogammaglobulinemia. Whole-exome sequencing identified a dinucleotide deletion (c.1580_1581del) in BTK, confirmed by Sanger sequencing and predicted to be disease causing by in silico functional prediction tools (Varsome and MutationTaster2) but was absent in the gnomAD database. This mutation resulted in a frameshift and premature termination (p.C527fs), which disrupted the protein structure. The mother was heterozygous at the mutation site, confirming her carrier status. Flow cytometric analysis of monocyte BTK expression showed it to be absent in the patient and bimodal in the mother. This study describes a novel BTK mutation in a defined hotspot and an atypical fungal phenotype in XLA. Further studies are required to understand the pathogenesis of fungal infection in XLA.

Effective, safe, and sustained correction of murine XLA using a UCOE-BTK promoter-based lentiviral vector

X-linked agammaglobulinemia (XLA) is an immune disorder caused by mutations in Bruton’s tyrosine kinase (BTK). BTK is expressed in B and myeloid cells, and its deficiency results in a lack of mature B cells and protective antibodies. We previously reported a lentivirus (LV) BTK replacement therapy that restored B cell development and function in Btk and Tec double knockout mice (a phenocopy of human XLA). In this study, with the goal of optimizing both the level and lineage specificity of BTK expression, we generated LV incorporating the proximal human BTK promoter. Hematopoietic stem cells from Btk^−/−Tec^−/− mice transduced with this vector rescued lineage-specific expression and restored B cell function in Btk^−/−Tec^−/− recipients. Next, we tested addition of candidate enhancers and/or ubiquitous chromatin opening elements (UCOEs), as well as codon optimization to improve BTK expression. An Eμ enhancer improved B cell rescue, but increased immunoglobulin G (IgG) autoantibodies. Addition of the UCOE avoided autoantibody generation while improving B cell development and function and reducing vector silencing. An optimized vector containing a truncated UCOE upstream of the BTK promoter and codon-optimized BTK cDNA resulted in stable, lineage-regulated BTK expression that mirrored endogenous BTK, making it a strong candidate for XLA therapy.

Update on Infections in Primary Antibody Deficiencies

Bacterial respiratory tract infections are the hallmark of primary antibody deficiencies (PADs). Because they are also among the most common infections in healthy individuals, PADs are usually overlooked in these patients. Careful evaluation of the history, including frequency, chronicity, and presence of other infections, would help suspect PADs. This review will focus on infections in relatively common PADs, discussing diagnostic challenges, and some management strategies to prevent infections.

Clinical and Genetic Profile of X-Linked Agammaglobulinemia: A Multicenter Experience From India

Background

There is paucity of literature on XLA from developing countries. Herein we report the clinical and molecular profile and outcome in a multicenter cohort of patients with XLA from India.

Methods

Data on XLA from all regional centers supported by the Foundation for Primary Immunodeficiency Diseases (FPID), USA and other institutions providing care to patients with PIDs were collated. Diagnosis of XLA was based on European Society for Immunodeficiencies (ESID) criteria.

Results

We received clinical details of 195 patients with a provisional diagnosis of XLA from 12 centers. At final analysis, 145 patients were included (137 'definite XLA' and eight 'probable/possible XLA'). Median age at onset of symptoms was 12.0 (6.0, 36.0) months and median age at diagnosis was 60.0 (31.5, 108) months. Pneumonia was the commonest clinical manifestation (82.6%) followed by otitis media (50%) and diarrhea (42%). Arthritis was seen in 26% patients while 23% patients developed meningitis. Bronchiectasis was seen in 10% and encephalitis (likely viral) in 4.8% patients. Pseudomonas aeruginosa was the commonest bacterial pathogen identified followed by Streptococcus pneumoniae, Staphylococcus aureus and Klebsiella pneumoniae. Molecular analysis revealed 86 variants in 105 unrelated cases. Missense variants in BTK gene were the most common (36%) followed by frameshift (22%) and nonsense variants (21%). Most pathogenic gene variants (53%) were clustered in the distal part of gene encompassing exons 14-19 encoding for the tyrosine kinase domain. Follow-up details were available for 108 patients. Of these, 12% had died till the time of this analysis. The 5-year and 10-year survival was 89.9% and 86.9% respectively. Median duration of follow-up was 61 months and total duration of follow-up was 6083.2 patient-months. All patients received intravenous immunoglobulin (IVIg) replacement therapy. However, in many patients IVIg could not be given at recommended doses or intervals due to difficulties in accessing this therapy because of financial reasons and lack of universal health insurance in India. Hematopoietic stem cell transplant was carried out in four (2.8%) patients.

Conclusion

There was a significant delay in the diagnosis and facilities for molecular diagnosis were not available at many centers. Optimal immunoglobulin replacement is still a challenge.

Case Report: A Case of X-Linked Agammaglobulinemia With High Serum IgE Levels and Allergic Rhinitis

X-linked Agammaglobulinemia (XLA) is a rare genetic disorder of B-lymphocyte differentiation, characterized by the absence or paucity of circulating B cells, markedly reduced levels of all serum immunoglobulin isotypes and lack of specific antibody production. Bruton Tyrosine Kinase (BTK) gene encodes a cytoplasmic tyrosine kinase involved in the B cell maturation and its mutation, blocking B cell differentiation at the pre-B cell stage, and is responsible for XLA. All domains may be affected by the mutation, and the many genotypes are associated with a wide range of clinical presentations. Little is known about genotype-phenotype correlation in this disorder, and factors influencing the phenotype of XLA are not clearly understood. In this report we present a unique case of a young patient affected by XLA. The disease was genetically diagnosed at birth due to a family history of XLA, but during follow up, it was characterized by a CD19+ B cell percentage consistently greater than 2%. He never suffered severe infections, but at two years of age, he developed persistent rhinitis. Thus, total serum IgE levels were measured and detected over the normal range, and specific allergic investigations showed sensitization to dust mites. Further immunological tests (BTK expression, functional “in vitro” B cell proliferation upon CpG stimulation, B cell subset analysis) explained these findings as possible manifestations of a mild XLA phenotype. XLA patients rarely present with allergic manifestations, which could warrant further investigation. High serum IgE levels could be a sign of a mild phenotype, but their role and the mechanisms underlying their production in XLA need to be clarified.

Distinct Clinical Features and Novel Mutations in Taiwanese Patients With X-Linked Agammaglobulinemia

Background: X-linked agammaglobulinemia (XLA) is caused by a mutation of the Bruton's tyrosine kinase (BTK) gene and is the most common genetic mutation in patients with congenital agammaglobulinemia. The aim of this study was to analyze the clinical features, genetic defects, and/or BTK expression in patients suspected of having XLA who were referred from the Taiwan Foundation of Rare Disorders (TFRD). Methods: Patients with recurrent bacterial infections in the first 2 years of life, serum IgG/A/M below 2 standard deviations of the normal range, and ≦2% CD19+B cells were enrolled during the period of 2004-2019. The frequency of infections, pathogens, B-lymphocyte subsets, and family pedigree were recorded. Peripheral blood samples were sent to our institute for BTK expression and genetic analysis. Results: Nineteen (from 16 families) out of 29 patients had BTK mutations, including 7 missense mutations, 7 splicing mutations, 1 nonsense mutation, 2 huge deletions, and 2 nucleotide deletions. Six novel mutations were detected: c.504G>T [p.K168N], c.895-2A>G [p.Del K290 fs 23^*], c.910T>G [p.F304V], c.1132T>C [p.T334H], c.1562A>T [p.D521V], and c.1957delG [Del p.D653 fs plus 45 a.a.]. All patients with BTK mutations had obviously decreased BTK expressions. Pseudomonas sepsis developed in 14 patients and led to both Shanghai fever and recurrent hemophagocytic lymphohistiocytosis (HLH). Recurrent sinopulmonary infections and bronchiectasis occurred in 11 patients. One patient died of pseudomonas sepsis and another died of hepatocellular carcinoma before receiving optimal treatment. Two patients with contiguous gene deletion syndrome (CGS) encompassing the TIMM8A/DDP1 gene presented with early-onset progressive post-lingual sensorineural Deafness, gradual Dystonia, and Optic Neuronopathy syndrome (DDON) or Mohr-Tranebjaerg syndrome (MTS). Conclusion: Pseudomonas sepsis was more common (74%) than recurrent sinopulmonary infections in Taiwanese XLA patients, and related to Shanghai fever and recurrent HLH, both of which were prevented by regular immunoglobulin infusions. Approximately 10% of patients belonged to CGS involving the TIMM8A/DDP1 gene and presented with the DDON/MTS phenotype in need of aggressive psychomotor therapy.