MSMD is a rare inherited primary immunodeficiency due to impaired IFN-γ-mediated immunity that leads to selective predisposition to clinical disease caused by weakly virulent mycobacteria, such as bacillus Calmette-Guerin (BCG) vaccines and non-tuberculous environmental mycobacteria (EM) (3). Here, IFNG is linked to Mendelian susceptibility to mycobacterial diseases.