De Novo Somatic Mosaicism of CYBB Caused by Intronic LINE-1 Element Insertion Resulting in Chronic Granulomatous Disease

Somatic mosaicism in genetic errors of immunity

Genetic mosaicism in somatic cells can lead to the presence of pathogenic variants in a subset of immune cells causing genetic errors of immunity, often phenocopying germline inborn errors of immunity. Over the last 2 decades, significant progress has been made in the identification of these disorders in patients, including discovery of new diseases. Diagnosis of disease-causing somatic mosaicism provides a target for treatment and monitoring of patients and has implications for genetic counseling. However, there continue to be barriers in the identification of somatic mosaicism, particularly for the clinical diagnosis of patients, based on the limitations of current diagnostic sequencing and analysis approaches. This review focuses on how somatic mosaicism can lead to genetic errors of immunity, the genes known to be associated with somatic genetic errors of immunity, and challenges in the field for accurate diagnosis of patients.

Case report: A cyclic neutropenia patient with ELANE mutation accompanied by hemophagocytic lymphohistiocytosis

Many inborn errors of immunity may accompany secondary hemophagocytic lymphohistiocytosis (HLH), a condition typically characterized by impaired cytotoxic T and NK cell function. A considerable proportion of HLH cases also stem from chronic granulomatosis with phagocytic dysfunction. However, the development of secondary HLH in patients with severe congenital neutropenia (SCN) or cyclic neutropenia (CyN) with abnormal phagocytic cell counts has been less frequently reported. Herein, we present a case of a pediatric patient with ELANE mutation-associated CyN who developed HLH subsequent to severe bacterial, fungal, and viral infections. Notable observations included impaired NK cell degranulation function (CD107a). To the best of our knowledge, this represents the first documented instance of HLH in patients with CyN attributed to an ELANE mutation. Thus, our study establishes a link between ELANE-related CyN and HLH, underscoring the importance of considering HLH as a potential complication in these patients.

Heterogeneous phenotype of a Chinese Familial WHIM syndrome with CXCR4V340fs gain-of-function mutation

Background

WHIM syndrome is a rare, autosomal dominant inborn error of immunity characterized by warts, hypogammaglobulinemia, infection, and myelokathexis. It is caused mainly by heterozygous mutations at the C-terminus of the C-X-C chemokine receptor type 4 (CXCR4) gene.

Methods

We described the detailed clinical, genetic, immunological and treatment characteristic of four WHIM patients from a single Chinese family.

Results

Here, we report four patients from a family carrying a variant of CXCR4 (c.1016_1017dupCT), which introduces a frameshift at codon V340, resulting in an extension of 14 amino acids (p.V340L fs*27). We provide and in-depth analysis of their clinical, genetic, immunological and treatment characteristic, noting that these patients exhibited an atypical clinical phenotype when compared to reported CXCR4R334X patients. Additionally, the frameshift variant CXCR4V340fs led to impaired receptor downregulation in patients' PBMCs, and in HEK293T cells transfected with the variant plasmids.

Conclusions

Our study provided detailed clinical features of four CXCR4V340fs WHIM patients from one Chinese family who presented atypical phenotype and enrich the spectrum of WHIM syndrome.

Somatic mutations in autoinflammatory and autoimmune disease

Somatic mutations (also known as acquired mutations) are emerging as common, age-related processes that occur in all cells throughout the body. Somatic mutations are canonically linked to malignant processes but over the past decade have been increasingly causally connected to benign diseases including rheumatic conditions. Here we outline the contribution of somatic mutations to complex and monogenic immunological diseases with a detailed review of unique aspects associated with such causes. Somatic mutations can cause early- or late-onset rheumatic monogenic diseases but also contribute to the pathogenesis of complex inflammatory and immune-mediated diseases, affect disease progression and define new clinical subtypes. Although even variants with a low variant allele fraction can be pathogenic, clonal dynamics could lead to changes over time in the proportion of mutant cells, with possible phenotypic consequences for the individual. Thus, somatic mutagenesis and clonal expansion have relevant implications in genetic testing and counselling. On the basis of both increased recognition of somatic diseases in clinical practice and improved technical and bioinformatic processes, we hypothesize that there will be an ever-expanding list of somatic mutations in various genes leading to inflammatory conditions, particularly in late-onset disease.

Fluoxetine Successfully Treats Intracranial Enterovirus E18 Infection in a Patient with CD79a Deficiency Arising from Segmental Uniparental Disomy of Chromosome 19

The pre BCR complex plays a crucial role in B cell production, and its successful expression marks the B cell differentiation from the pro-B to pre-B. The CD79a and CD79b mutations, encoding Igα and Igβ respectively, have been identified as the cause of autosomal recessive agammaglobulinemia (ARA). Here, we present a case of a patient with a homozygous CD79a mutation, exhibiting recurrent respiratory infections, diarrhea, growth and development delay, unique facial abnormalities and microcephaly, as well as neurological symptoms including tethered spinal cord, sacral canal cyst, and chronic enteroviral E18 meningitis. Complete blockade of the early B cell development in the bone marrow of the patient results in the absence of peripheral circulating mature B cells. Whole exome sequencing revealed a Loss of Heterozygosity (LOH) of approximately 19.20Mb containing CD79a on chromosome 19 in the patient. This is the first case of a homozygous CD79a mutation caused by segmental uniparental diploid (UPD). Another key outcome of this study is the effective management of long-term chronic enteroviral meningitis using a combination of intravenous immunoglobulin (IVIG) and fluoxetine. This approach offers compelling evidence of fluoxetine's utility in treating enteroviral meningitis, particularly in immunocompromised patients.

Legacy and emerging per- and polyfluoroalkyl substances suppress the neutrophil respiratory burst

Per- and polyfluoroalkyl substances (PFASs) are used in a multitude of processes and products, including nonstick coatings, food wrappers, and fire-fighting foams. These chemicals are environmentally-persistent, ubiquitous, and can be detected in the serum of 98% of Americans. Despite evidence that PFASs alter adaptive immunity, few studies have investigated their effects on innate immunity. The report here presents results of studies that investigated the impact of nine environmentally-relevant PFASs [e.g. perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid potassium salt (PFOS-K), perfluorononanoic acid (PFNA), perfluorohexanoic acid (PFHxA), perfluorohexane sulfonic acid (PFHxS), perfluorobutane sulfonic acid (PFBS), ammonium perfluoro(2-methyl-3-oxahexanoate) (GenX), 7H-perfluoro-4-methyl-3,6-dioxa-octane sulfonic acid (Nafion byproduct 2), and perfluoromethoxyacetic acid sodium salt (PFMOAA-Na)] on one component of the innate immune response, the neutrophil respiratory burst. The respiratory burst is a key innate immune process by which microbicidal reactive oxygen species (ROS) are rapidly induced by neutrophils in response to pathogens; defects in the respiratory burst can increase susceptibility to infection. The study here utilized larval zebrafish, a human neutrophil-like cell line, and primary human neutrophils to ascertain whether PFAS exposure inhibits ROS production in the respiratory burst. It was observed that exposure to PFHxA and GenX suppresses the respiratory burst in zebrafish larvae and a human neutrophil-like cell line. GenX also suppressed the respiratory burst in primary human neutrophils. This report is the first to demonstrate that these PFASs suppress neutrophil function and support the utility of employing zebrafish larvae and a human cell line as screening tools to identify chemicals that may suppress human immune function.

Molecular Challenges in the Diagnosis of X-Linked Chronic Granulomatous Disease: CNVs, Intronic Variants, Skewed X-Chromosome Inactivation, and Gonosomal Mosaicism

Chronic granulomatous disease (CGD) is a prototypical inborn error of immunity affecting phagocytes, in which these cells are unable to produce reactive oxygen species. CGD is caused by defects in genes encoding subunits of the NADPH oxidase enzyme complex (CYBA, CYBB, CYBC1, NCF1, NCF2, NCF4); inflammatory responses are dysregulated, and patients are highly susceptible to recurrent severe bacterial and fungal infections. X-linked CGD (XL-CGD), caused by mutations in the CYBB gene, is the most common and severe form of CGD. In this study, we describe the analytical processes undertaken in 3 families affected with XL-CGD to illustrate several molecular challenges in the genetic diagnosis of this condition: in family 1, a girl with a heterozygous deletion of CYBB exon 13 and skewed X-chromosome inactivation (XCI); in family 2, a boy with a hemizygous deletion of CYBB exon 7, defining its consequences at the mRNA level; and in family 3, 2 boys with the same novel intronic variant in CYBB (c.1151 + 6 T > A). The variant affected the splicing process, although a small fraction of wild-type mRNA was produced. Their mother was a heterozygous carrier, while their maternal grandmother was a carrier in form of gonosomal mosaicism. In summary, using a variety of techniques, including an NGS-based targeted gene panel and deep amplicon sequencing, copy number variation calling strategies, microarray-based comparative genomic hybridization, and cDNA analysis to define splicing defects and skewed XCI, we show how to face and solve some uncommon genetic mechanisms in the diagnosis of XL-CGD.

Multiple Immune Defects in Two Patients with Novel DOCK2 Mutations Result in Recurrent Multiple Infection Including Live Attenuated Virus Vaccine

The dedicator of cytokinesis 2(DOCK2) protein, an atypical guanine nucleotide exchange factor (GEFs), is a member of the DOCKA protein subfamily. DOCK2 protein deficiency is characterized by early-onset lymphopenia, recurrent infections, and lymphocyte dysfunction, which was classified as combined immune deficiency with neutrophil abnormalities as well. The only cure is hematopoietic stem cell transplantation. Here, we report two patients harboring four novel DOCK2 mutations associated with recurrent infections including live attenuated vaccine-related infections. The patient's condition was partially alleviated by symptomatic treatment or intravenous immunoglobulin. We also confirmed defects in thymic T cell output and T cell proliferation, as well as aberrant skewing of T/B cell subset TCR-Vβ repertoires. In addition, we noted neutrophil defects, the weakening of actin polymerization, and BCR internalization under TCR/BCR activation. Finally, we found that the DOCK2 protein affected antibody affinity although with normal total serum immunoglobulin. The results reported herein expand the clinical phenotype, the pathogenic DOCK2 mutation database, and the immune characteristics of DOCK2-deficient patients.