Isolated and syndromic MSMD comprises now a group of genetic disorders caused by mutations in 16 published genes (see Table 1), all of them being involved in IFN-γ-mediated immunity, including impaired IFN-γ production (IL12B, IL12RB1, IL12RB2, IL23R, IRF8, TYK2, ISG15, IKBKG, RORC) or impaired cellular responses to IFN-γ (IFNGR1, IFNGR2, JAK1, STAT1, IRF8, CYBB, SPPL2A) (Bustamante 2020; Martinez-Barricarte et al. 2018; Rosain et al. 2019). The gene discussed is IL12RB1; the disease is Mendelian susceptibility to mycobacterial diseases.