Variants of MSMD-causing genes disrupt the production of IFNγ (IFNG, IL12B, IL12RB1, IL12RB2, IL23R, ISG15, MCTS1, RORC, TBX21, TYK2), the response to IFNγ (CYBB, JAK1, IFNGR1, IFNGR2, STAT1, USP18) or both (IRF1, IRF8, NEMO, SPPL2A), or the recruitment of monocytes (CCR2)7–14. The gene discussed is CYBB; the disease is Mendelian susceptibility to mycobacterial diseases.