Monoallelic loss-of-function variants in STAT1 cause isolated MSMD, while biallelic loss-of-function variants in STAT1 lead to syndromic MSMD, clinically characterized by concurrent mycobacterial infections with other pathogens encompassing viruses, bacteria, and fungi, demonstrating potential lethality in clinical cases (Ye et al., 2022; Casanova et al., 2024; Kagawa et al., 2017). Here, STAT1 is linked to Mendelian susceptibility to mycobacterial diseases.