There is a wide variety of functional tests available for MSMD diagnosis, such as ELISA for IFN-γ and IL-12, STAT1 phosphorylation, and the detection of anti-IFN-γ autoantibodies [48,57,67]; however, the use of these techniques requires qualified staff, making the full diagnosis of MSMD only possible in specialized immunology laboratories. Here, IFNG is linked to Mendelian susceptibility to mycobacterial diseases.