Disseminated BCGitis with Interferon-Gamma Receptor Deficiency: An Example of an Extremely Rare Illness.

Mendelian susceptibility to mycobacterial disease (MSMD) is a group of inherited inborn errors of immunity due to approximately 21 genetic defects. Interferon-gamma receptor type 1 (IFNGR1) deficiency was the first disease described in this group. IFNGR1 can cause a loss of cellular responsiveness to interferon-γ (IFN-γ). Mycobacterial infections occur due to gene mutations that encode the IFNGR1 chain, leading to a loss of cellular responsiveness to type II IFN-γ, which plays a significant role in controlling intracellular bacteria. MSMD is characterized by increased susceptibility to environmental mycobacteria and low virulent mycobacteria like Bacillus Calmette-Guerin (BCG) vaccine strains. Careful and timely interventions for diagnosis and management are required if a patient develops clinical manifestations after BCG vaccination. Diagnosis can be made by gene study, and bone marrow transplantation remains the mainstay of treatment.