Germline pathogenic variants in the mucosa-associated lymphoid tissue lymphoma translocation gene 1 (MALT1) encodes a caspase-like protease that plays a crucial role in the caspase recruitment domain (CARD)-B-cell lymphoma 10 (BCL10)-MALT1 (CBM) complex. This complex mediates the activation of nuclear factor-kB (NF-kB) pathway and are associated with diverse human diseases including combine immunodeficiency (CID), lymphoproliferation and others. This study aimed to determine the underlying cause of immune deficiency and immune dysregulation in a patient presented with recurrent respiratory infections, aphthous ulcers, dermatitis, chronic diarrhea, failure to thrive and early death. Clinical and laboratory records were reviewed. Patients underwent next-generation sequencing (NGS), and analysis of genomic DNA was performed on the patient and her parents. Lymphocyte subsets, MALT1 expression and NF-kB signaling was evaluated by flow cytometry, RT-PCR and immunoblotting. The patient carried a novel pathogenic biallelic loss-of-function variant in MALT1 (c.1411G > A; p.D471N) located in the caspase-like domain, leading to severely reduced MALT1 protein expression. Impaired CBM-mediated NF-κB activation was confirmed by reduced phosphorylation of the p65 subunit, resulting in deficient production of IL-2 and TNF-α. This functional defect caused lower Tfr and Treg cells, a normal proportion of Tfh cells, with higher expression of activation markers PD-1 and ICOS. The patient displayed low NK cell and B cell counts, together with a developmental block at the transitional B cell stage. Additionally, the proportion of marginal zone-like B cells (MZB-like) was markedly decreased, indicating impaired B cell differentiation. Human MALT1 deficiency causes profound CID by impairing CBM-mediated NF-kB signaling and MALT1-paracaspase activity. Consistent with the reported variants located in the caspase-like domain, our patient presented with an inflammatory phenotype, supporting the notion that the MALT1 D471N mutation phenocopies a partial loss of both MALT1 scaffolding function and paracaspase activity. Prompt hematopoietic stem cell transplantation (HSCT) is highly recommended as an effective therapy for MALT1 deficiency.

Primary atopic disorders (PAD) are monogenic disorders caused by pathogenic gene variants encoding proteins that are key for the maintenance of a healthy skin barrier and a well-functioning immune system. Physicians face the challenge to find single, extremely rare PAD patients/families among the millions of individuals with common allergic diseases. We describe case scenarios with signature PAD. We review the literature and deduct specific clinical red flags for PAD detection. They include a positive family history and/or signs of pathological susceptibility to infections, immunodysregulation, or syndromic disease. Results of conventional laboratory and most immunological lab studies are not sufficient to make a definitive diagnosis of PAD. In the past, multistep narrowing of differential diagnoses by various immunological and other laboratory tests led to testing of single genes or gene panel analyses, which was a time-consuming and often unsuccessful approach. The implementation of whole-genomic analyses in the routine diagnostics has led to a paradigm shift. Upfront genome-wide analysis by whole genome sequencing (WGS) will shorten the time to diagnosis, save patients from unnecessary investigations, and reduce morbidity and mortality. We propose a rational, clinical landmark-based approach for deciding which cases pass the filter for carrying out early WGS. WGS result interpretation requires a great deal of caution regarding the causal relationship of variants in PAD phenotypes and absence of proof by adequate functional tests. In case of negative WGS results, a re-iteration attitude with re-analyses of the data (using the latest data base annotation)) may eventually lead to PAD diagnosis. PAD, like many other rare genetic diseases, will only be successfully managed, if physicians from different clinical specialties and geneticists interact regularly in multidisciplinary conferences.

Inborn errors of the CARD11-BCL10-MALT1 (CBM) signalosome have recently been shown to underlie severe combined immunodeficiency (SCID) and combined immunodeficiency (CID) with variable immunological and clinical phenotypes, and patients usually present with recurrent bacterial, viral, and fungal infections, periodontal disease, enteropathy, dermatitis, and failure to thrive. In the present study, we describe the clinical and immunological characteristics of an Egyptian patient with a mutation in the MALT1 gene. The patient suffered from an itchy exfoliative skin rash and eczematous lesions over his face and flexural surface of the limbs. He also had dental enamel erosion, repeated attacks of diarrhea, and pneumonia. He had elevated serum IgE and normal B- and T-lymphocyte subset counts, but there was an arrest in the B-cell maturation. DOCK8 expression on the lymphocytes by flow cytometry was normal. Next-generation sequencing revealed a novel homozygous variant in the MALT1 gene (c.762dup in exon 5 of 17; p.Ile255TyrfsTer10); this variant is likely pathogenic, thus supporting the genetic diagnosis of immunodeficiency-12 (IMD12). Although the presence of eczema, recurrent sinopulmonary, and staphylococcal infections are suggestive of DOCK8 deficiency, they are also a finding in CARD11 and MALT1 deficiency. Thus, whenever DOCK 8 has been excluded, the molecular diagnosis is mandatory as this could lead to discovering more patients hence better understanding and reporting of the phenotype and natural history of the disease especially since there are very few documented cases. Early diagnosis will also enable the proper patient management by hematopoietic stem cell transplantation (HSCT) prior to the establishment of infections and pulmonary damage leading to a better outcome.

Patients with primary immunodeficiency disorders (PIDs) often suffer from recurrent infections because of their inappropriate immune response to both common and less common pathogens. These patients may present with unique and severe cutaneous infectious manifestations that are not common in healthy individuals and may be more challenging to diagnose and treat. To describe a cohort of patients with PIDs with atypical presentations of skin infections, who posed a diagnostic and/or therapeutic challenge. This is a retrospective study of pediatric patients with PID with atypical presentations of infections, who were treated at the immunodeficiency specialty clinic and the pediatric dermatology clinic at the Sheba Medical Center between September 2012 and August 2022. Epidemiologic data, PID diagnosis, infectious etiology, presentation, course, and treatment were recorded. Eight children with a diagnosis of PID were included, five of whom were boys. The average age at PID diagnosis was 1.7 (±SD 3.2) years. The average age of cutaneous infection was 6.9 (±SD 5.9) years. Three patients were born to consanguineous parents. The PIDs included the following: common variable immunodeficiency, severe combined immunodeficiency, DOCK8 deficiency, ataxia telangiectasia, CARD11 deficiency, MALT1 deficiency, chronic granulomatous disease, and a combined cellular and humoral immunodeficiency syndrome of unknown etiology. The infections included the following: ulcerative-hemorrhagic varicella-zoster virus (two cases) atypical fungal and bacterial infections, resistant Norwegian scabies, giant perianal verrucae (two cases), and diffuse molluscum contagiosum. In this case series, we present unusual manifestations of infectious skin diseases in pediatric patients with PID. In some of the cases, recognition of the infectious process prompted life-saving treatment. Increasing familiarity with these dermatological manifestations, as well as keeping a high index of suspicion, is important to enabling early diagnosis of cutaneous infections in PIDs and initiation of prompt suitable treatment.

MALT1 is a core component of the CARD11-BCL10-MALT1 (CBM) signalosome, in which it acts as a scaffold and a protease to bridge T cell receptor (TCR) ligation to immune activation. As a scaffold, MALT1 binds to TRAF6, and T cell-specific TRAF6 ablation or destruction of MALT1-TRAF6 interaction provokes activation of conventional T (Tconv) effector cells. In contrast, MALT1 protease activity controls the development and suppressive function of regulatory T (Treg) cells in a T cell-intrinsic manner. Thus, complete loss of TRAF6 or selective inactivation of MALT1 catalytic function in mice skews the immune system towards autoimmune inflammation, but distinct mechanisms are responsible for these immune disorders. Here we demonstrate that TRAF6 deletion or MALT1 paracaspase inactivation are highly interdependent in causing the distinct immune pathologies. We crossed mice with T cell-specific TRAF6 ablation (Traf6-ΔT) and mice with a mutation rendering the MALT1 paracaspase dead in T cells (Malt1 PD-T) to yield Traf6-ΔT;Malt1 PD-T double mutant mice. These mice reveal that the autoimmune inflammation caused by TRAF6-ablation relies strictly on the function of the MALT1 protease to drive the activation of Tconv cells. Vice versa, despite the complete loss of Treg cells in Traf6-ΔT;Malt1 PD-T double mutant mice, inactivation of the MALT1 protease is unable to cause autoinflammation, because the Tconv effector cells are not activated in the absence of TRAF6. Consequentially, combined MALT1 paracaspase inactivation and TRAF6 deficiency in T cells mirrors the immunodeficiency seen upon T cell-specific MALT1 ablation.