A Novel Homozygous Stop Mutation in IL23R Causes Mendelian Susceptibility to Mycobacterial Disease

PURPOSE: Mendelian susceptibility to mycobacterial disease (MSMD) is caused by inborn errors of IFN-γ immunity. The most frequent genetic defects are found in IL12 or a subunit of its receptor. IL23R deficiency in MSMD has only been reported once, in two pediatric patients from the same kindred with isolated disseminated Bacille Calmette-Guérin disease. We evaluated the impact of a homozygous stop mutation in IL23R (R381X), identified by whole exome sequencing, in an adult patient with disseminated non-tuberculous mycobacterial disease. METHODS: We performed functional validation of the R381X mutation by evaluating IL23R expression and IL-23 signaling (STAT3 phosphorylation, IFN-γ production) in primary cells (PBMCs, EBV-B cells) and cell lines (HeLa) with or without back-complementation of wild-type IL23R. RESULTS: We report on a 48-year-old male with disseminated non-tuberculous mycobacterial disease. We identified and characterized a homozygous loss-of-function stop mutation underlying IL23R deficiency, resulting in near absent expression of membrane bound IL23R. IL23R deficiency was characterized by impaired IL-23-mediated IFN-γ secretion in CD4(+), CD8(+) T, and mucosal-associated invariant T (MAIT) cells, and low frequencies of circulating Th17 (CD3(+)CD45RA(−)CCR4(+)CXCR3(−)RORγT(+)), Th1* (CD45RA(−)CCR4(−)CXCR3(+)RORγT(+)), and MAIT (CD3(+)CD8(+)Vα7.2(+)CD161(+)) cells. Although the patient did not have a history of recurrent fungal infections, impaired Th17 differentiation and blunted IL-23-mediated IL-17 secretion in PBMCs were observed. CONCLUSION: We demonstrate that impaired IL-23 immunity caused by a homozygous R381X mutation in IL23R underlies MSMD, corroborating earlier findings with a homozygous p.C115Y IL23R mutation. Our report further supports a model of redundant contribution of IL-23- to IL-17-mediated anti-fungal immunity.1 SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10875-022-01320-7.