Mutations in the genes coding for cytokines, receptors, second messengers, and transcription factors of interferon gamma (IFN-γ) immunity cause Mendelian susceptibility to mycobacterial disease (MSMD). We report the case of a 7-year-old male patient with partial dominant (PD) IFN-γ receptor 1 deficiency who had suffered from multifocal osteomyelitis attributable to bacille Calmette-Guérin vaccination since the age of 18 months. He developed hemophagocytic lymphohistiocytosis (HLH), a hyper-inflammatory complication, and died with multiorgan dysfunction, despite having been diagnosed and treated relatively early. Patients with PD IFN-γR1 deficiency usually have good prognosis and might respond to human recombinant subcutaneous IFN-γ. Several monogenic congenital defects have been linked to HLH, a catastrophic "cytokine storm" that is usually ascribed to lymphocyte dysfunction and thought to be triggered by interferon gamma. This is the sixth patient with both MSMD and HLH of whom we are aware. The fact that patients with macrophages that cannot respond to IFN-γ still develop HLH, bring these assumptions into question.
Keywords: Mendelian susceptibility to mycobacterial disease; bacille Calmette–Guérin vaccine; hemophagocytic lymphohistiocytosis; human recombinant interferon gamma; interferon gamma receptor 1 deficiency; macrophage activation syndrome; multiorgan dysfunction; osteomyelitis.