Since the recognition of MSMD 25 years ago, variants of 22 genes have been implicated in this condition (CCR2, CYBB, IFNG, IFNGR1, IFNGR2, IL12B, IL12RB1, IL12RB2, IL23R, IRF1, IRF8, ISG15, JAK1, MCTS1, NEMO, RORC, SPPL2A, STAT1, TBX21, TYK2, USP18, and ZNFX1) [1–9]. Here, IRF1 is linked to Mendelian susceptibility to mycobacterial diseases.