BACKGROUND: Inborn errors of IL-12/IL-23-IFNγ immunity underlie Mendelian susceptibility to mycobacterial diseases (MSMD), a group of immunodeficiencies characterized by a highly selective susceptibility to weakly virulent strains of mycobacteria, such as non-tuberculous mycobacteria (NTM) and bacillus Calmette-Guérin (BCG). Cutaneous mycobacterial infections are common in MSMD and may represent a red flag for this immunodeficiency. OBJECTIVES: We present a case series of four paediatric patients with MSMD, specifically with IFNγR1 and STAT1 deficiencies, and cutaneous NTM/BCG infections to increase awareness of this immunodeficiency, which may, in some cases, be intercepted by the dermatologist and thus timely referred to the immunologist. MATERIALS & METHODS: Clinical, laboratory and genetic investigations of the four paediatric patients with MSMD are presented. RESULTS: All four presented patients experienced early complications after BCG vaccination. Two patients suffered recurrent mycobacteriosis, one patient experienced delayed BCG reactivation, and one patient died of disseminated avian mycobacteriosis. The dermatological manifestation in these patients included destructive nasal ulcerations, scrofuloderma of various sites and lupus vulgaris. All patients had a normal basic immune phenotype. CONCLUSION: The presented cases demonstrate that NTM/BCG infections in otherwise seemingly immunocompetent patients should raise suspicion of MSMD. This is of utmost importance as specific therapeutic approaches, such as IFNγ treatment or haematopoietic stem cell transplantation, may be employed to improve the disease outcome.

• Keywords
• MSMD, mendelian susceptibility to mycobacterial diseases, IFNγR1, STAT1, inborn error of immunity, non-tuberculous mycobacteria, BCG, necrotizing granulomas, antituberculotics,
• MeSH
• Skin Diseases, Bacterial * MeSH
• BCG Vaccine adverse effects   MeSH
• Genetic Predisposition to Disease MeSH
• Interferon-gamma MeSH
• Interleukin-12 MeSH
• Interleukin-23 MeSH
• Humans MeSH
• Mycobacterium Infections * genetics   MeSH
• Immunologic Deficiency Syndromes * complications   genetics   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Case Reports MeSH
• Names of Substances
• BCG Vaccine MeSH
• Interferon-gamma MeSH
• Interleukin-12 MeSH
• Interleukin-23 MeSH