IFNGR1 and Mendelian susceptibility to mycobacterial diseases: Interferon-γ receptor 1 (IFNGR1) deficiency is a rare immune deficiency characterized by selective susceptibility to mycobacterial disease caused by genetic mutations in the IFNGR1 gene.1 It comprises about 8% of patients in a group of diseases referred collectively as to Mendelian susceptibility to mycobacterial disease (MSMD) syndromes.2 Patients with MSMD feature genetic defects in genes encoding components of the interleukin (IL)-12/23-IFN-γ (interferon-γ) axis, a critical mechanism in the clearance of intracellular infections.3