Individuals with impaired T-cell-mediated immunity (eg SCID or HIV infection) are highly susceptible to mycobacterial infections, including infections caused by poorly pathogenic mycobacterial species (nontuberculous mycobacteria and BCG). However, disseminated life-threatening infections by these organisms may also occur in the absence of a recognized primary or secondary immunodeficiency. Genetic analysis of affected kindred to date have identified mutations in seven different genes that participate in the production or response to IFN-γ. These patients are classified under the heading Mendelian susceptibility to mycobacterial disease (MSMD). The genetic lesion s responsible for MSMD affect the integrity of IL-12/23-dependent IFN-γ pathway.