ISG15 and Mendelian susceptibility to mycobacterial diseases: In a study on Mendelian susceptibility to mycobacterial disease (MSMD), Bogunovic et al. identified patients with a genetic loss of ISG15 who could not produce IFN-γ in response to the Mycobacterium bovis Bacille Calmette-Guérin (BCG) vaccine, leading to severe disease [23].