MSMD-causing mutations have been identified in eight autosomal genes (IFNGR1, IFNGR2, STAT1, IL12B, IL12RB1, IRF8, ISG15, and TYK2) and two X-linked genes (IKBKG and CYBB) (Bogunovic et al. 2012; Bustamante et al. 2011; Filipe-Santos et al. 2006; Hambleton et al. 2011; Haverkamp et al. 2014; Prando et al. 2013) resulting in impaired IFN-γ-mediated immunity (Casanova and Abel 2002; de Beaucoudrey et al. 2010). The gene discussed is IL12B; the disease is Mendelian susceptibility to mycobacterial diseases.