IFNGR1 and Mendelian susceptibility to mycobacterial diseases: However, only three etiologies of isolated MSMD are truly Mendelian, i.e. with complete clinical penetrance1: autosomal recessive (AR) complete IFN-γ, IFN-γR1, and IFN-γR2 deficiencies (Figure S1B)4,5,12–15.