STAT1 and Mendelian susceptibility to mycobacterial diseases: Whereas STAT1 deficiency, together with other genetic abnormalities in the macrophage - T cell circuit governing IL12-IFNγ immunity, gives rise to MSMD, STAT2 deficiency was reported in 2013 to cause a narrow infectious phenotype with a fulminating disease course in a 5-year old child following MMR vaccination (73) (Figure 3).