X-linked recessive (XR) complete MCTS1 deficiency underlies Mendelian susceptibility to mycobacterial disease (MSMD) in patients with bacille Calmette-Guérin (BCG) disease. We investigated the genotypic and phenotypic landscape of four new unrelated families from four distinct countries. Three patients had adverse reactions to the BCG vaccine, whereas another patient was not vaccinated with BCG and had an infection with Mycobacterium abscessus at 16 years of age. Whole-exome sequencing of the probands revealed hemizygosity for rare germline MCTS1 variants. In addition to a previously reported loss-of-expression (LOE) and loss-of-function (LOF) variant, we identified three new MCTS1 variants. The p.L170* and E60Kfs5* variants are LOF, whereas p.W175* is hypomorphic when overexpressed. Thus, we report four new MSMD patients with complete or partial forms of XR MCTS1 deficiency, including three patients with newly discovered genotypes. A diagnosis of partial or complete XR MCTS1 deficiency should be considered in boys and men with MSMD displaying mycobacterial infection.

Indicine cattle exhibit superior resistance to Mycobacterium bovis infection compared to taurine breeds, revealing divergent genetic mechanisms underlying bovine tuberculosis (bTB) resilience. Previous research has demonstrated that Cytochrome b-245 (CYBB) gene variants are associated with Mendelian susceptibility to Mycobacterium tuberculosis complex (MTBC) infections. In this study, we analyzed the X-chromosomal sequences from 258 female cattle and identified a divergent missense variant (L237M) in the CYBB gene. This variant occurs at high frequencies in indicine populations. Functional studies using murine macrophages revealed that CYBB  L237M mitigates M. tuberculosis-induced ferroptosis by elevating glutathione synthesis and glutathione peroxidase 4 expression. Mechanistically, the L237M substitution enhances the stability of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2 (NOX2) and p22phox complex (NOX2-p22), which is critical for the generation of phagosomal reactive oxygen species and bacterial clearance. Our findings demonstrate that CYBB  L237M promotes intracellular MTBC elimination through ferroptosis suppression, partially explaining the superior bTB resistance of indicine cattle. This study highlights X-chromosomal genetic variation as an evolutionary driver of innate immunity against mycobacterial infections, with implications for breeding strategies and host-directed tuberculosis therapies. The CYBB variant exemplifies how cattle subspecies divergence can illuminate conserved antimicrobial defense mechanisms in mammals.

Mendelian susceptibility to mycobacterial diseases (MSMD) refers to a group of genetic conditions predisposing an individual to environmental mycobacteria and other intracellular pathogens, leading to disseminated infection. Nine MSMD genes have been identified, which include seven autosomal (IFNGR1, IFNGR2, STAT1, IL12B, IL12RB1, ISG15, and IRF8) and two X-linked (NEMO and CYBB) genes. MSMD patients present with disseminated BCGosis or with symptoms of non-tuberculous Mycobacterium (NTM). Host defense mechanisms, such as the interferon (IFN) gamma and IL-12 pathways, which activate macrophages, play a crucial role in combating the Mycobacterium species. Treatment with interferon gamma and hematopoietic stem cell transplantation holds promise.

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 immunity (IEI) are a heterogeneous group of monogenic disorders that include primary immunodeficiency's and other disorders affecting different aspects of the immune system. Next-Generation Sequencing (NGS) is an essential tool to diagnose IEI. We report our 3-year experience in setting up facilities for NGS for diagnosis of IEI in Chandigarh, North India. We used a targeted, customized gene panel of 44 genes known to result in IEI. Variant analysis was done using Ion Reporter software. The in-house NGS has enabled us to offer genetic diagnoses to patients with IEI at minimal costs. Of 121 patients who were included pathogenic variants were identified in 77 patients. These included patients with Chronic Granulomatous Disease, Severe Combined Immune Deficiency, leukocyte adhesion defect, X-linked agammaglobulinemia, Ataxia Telangiectasia, Hyper-IgE syndrome, Wiskott Aldrich syndrome, Mendelian susceptibility to mycobacterial diseases, Hyper-IgM syndrome, autoimmune lymphoproliferative syndrome, and GATA-2 deficiency. This manuscript discusses the challenges encountered while setting up and running targeted NGS for IEI in our unit. Genetic diagnosis has helped our patients with IEI in genetic counselling, prenatal diagnosis, and accessing appropriate therapeutic options.