XDR TB in a case of IL12Rβ1 deficiency: a case report of Mendelian Susceptibility to Mycobacterial Disease from India

Disseminated multidrug-resistant tuberculosis and SARS-CoV-2 co-infection in a child with IL-12Rβ1 deficiency

Mendelian Susceptibility to Mycobacterial Disease describes a spectrum of inherited defects, of which complete deficiency of the interleukin-12 receptor β subunit 1 (IL-12Rβ1) is the most common cause. This condition results in a predisposition to severe disease caused by mycobacteria. We report a case of disseminated multidrug-resistant tuberculosis with extensive central nervous system affection with SARS-CoV-2 co-infection, in a 4-year-old child with IL-12Rβ1 complete deficiency.

Clinical and Molecular Findings in Mendelian Susceptibility to Mycobacterial Diseases: Experience From India

Mendelian Susceptibility to Mycobacterial diseases (MSMD) are a group of innate immune defects with more than 17 genes and 32 clinical phenotypes identified. Defects in the IFN-γ mediated immunity lead to an increased susceptibility to intracellular pathogens like mycobacteria including attenuated Mycobacterium bovis-Bacillus Calmette-Guérin (BCG) vaccine strains and non-tuberculous environmental mycobacteria (NTM), Salmonella, fungi, parasites like Leishmania and some viruses, in otherwise healthy individuals. Mutations in the IL12RB1 gene are the commonest genetic defects identified. This retrospective study reports the clinical, immunological, and molecular characteristics of a cohort of 55 MSMD patients from 10 centers across India. Mycobacterial infection was confirmed by GeneXpert, Histopathology, and acid fast bacilli staining. Immunological workup included lymphocyte subset analysis, Nitro blue tetrazolium (NBT) test, immunoglobulin levels, and flow-cytometric evaluation of the IFN-γ mediated immunity. Genetic analysis was done by next generation sequencing (NGS). Disseminated BCG-osis was the commonest presenting manifestation (82%) with a median age of presentation of 6 months due to the practice of BCG vaccination at birth. This was followed by infection with Salmonella and non-typhi Salmonella (13%), Cytomegalovirus (CMV) (11%), Candida (7%), NTM (4%), and Histoplasma (2%). Thirty-six percent of patients in cohort were infected by more than one organism. This study is the largest cohort of MSMD patients reported from India to the best of our knowledge and we highlight the importance of work up for IL-12/IL-23/ISG15/IFN-γ circuit in all patients with BCG-osis and suspected MSMD irrespective of age.

Case Report: Reactive Lymphohistiocytic Proliferation in Infant With a Novel Nonsense Variant of IL2RG Who Received BCG Vaccine

We present here a male young infant with X-linked severe combined immunodeficiency (MIM#300400) due to the novel nonsense variant of IL2RG (interleukin 2 receptor, gamma; MIM#308380), NM_000206.2(IL2RG):c.820_823dup p.Ser275Asnfs^*29. He developed aggressive reactive lymphohistiocytic proliferation after receiving the live-attenuated Bacillus Calmette-Guérin (BCG) vaccine at birth. This report advocates for modifying the current practice of early use of BCG. The natural history of his disease also suggests considering IL2RG variants as a potential cause of "X-linked recessive Mendelian susceptibility to mycobacterial disease" (MSMD). His reactive lymphohistiocytic proliferation and massive hepatosplenomegaly simulated hemophagocytic lymphohistiocytosis (HLH, likely triggered by the BCG disease). This entity was masked by the absence of fever and markedly elevated inflammatory biomarkers. Thus, his findings stimulate discussion on the need to modify the diagnostic criteria of HLH, in order to accommodate conditions, such IL2RG variants that block systemic inflammation.

Mendelian susceptibility to mycobacterial disease-Challenges in hematopoietic stem cell transplantation

We present our experience in the hematopoietic stem cell transplantation (HSCT) in two children diagnosed with Mendelian susceptibility to mycobacterial diseases. The first child underwent a haploidentical HSCT with posttransplant cyclophosphamide using a reduced intensity conditioning following which he had primary graft failure. He was subsequently found to have interferon-γ1 receptor deficiency. He had immune reconstitution and is on antitubercular therapy. The second child diagnosed with IL12RB1 gene mutation underwent matched sibling donor HSCT with myeloablative conditioning following pretransplant immunosuppression with fludarabine and dexamethasone. He is 13 months post-HSCT with complete and remains disease free.

Inherited and acquired immunodeficiencies underlying tuberculosis in childhood

Tuberculosis (TB), caused by Mycobacterium tuberculosis (M.tb) and a few related mycobacteria, is a devastating disease, killing more than a million individuals per year worldwide. However, its pathogenesis remains largely elusive, as only a small proportion of infected individuals develop clinical disease either during primary infection or during reactivation from latency or secondary infection. Subacute, hematogenous, and extrapulmonary disease tends to be more frequent in infants, children, and teenagers than in adults. Life-threatening primary TB of childhood can result from known acquired or inherited immunodeficiencies, although the vast majority of cases remain unexplained. We review here the conditions conferring a predisposition to childhood clinical diseases caused by mycobacteria, including not only M.tb but also weakly virulent mycobacteria, such as BCG vaccines and environmental mycobacteria. Infections with weakly virulent mycobacteria are much rarer than TB, but the inherited and acquired immunodeficiencies underlying these infections are much better known. Their study has also provided genetic and immunological insights into childhood TB, as illustrated by the discovery of single-gene inborn errors of IFN-γ immunity underlying severe cases of TB. Novel findings are expected from ongoing and future human genetic studies of childhood TB in countries that combine a high proportion of consanguineous marriages, a high incidence of TB, and an excellent clinical care, such as Iran, Morocco, and Turkey.