Disseminated Mycobacterium simiae Infection in a Patient with Complete IL-12p40 Deficiency

Mendelian susceptibility to mycobacterial disease (MSMD) is a rare group of genetic disorders characterized by infections with weakly virulent environmental mycobacteria (EM) or Mycobacterium bovis bacillus Calmette-Guérin (BCG). Herein, we described the case of a 4.5-year-old boy with protein-losing enteropathy, lymphoproliferation, and candidiasis, who was found to have disseminated Mycobacterium simiae infection. A homozygous mutation in the IL12B gene, c.527_528delCT (p.S176Cfs*12) was identified, responsible for the complete IL-12p40 deficiency. He was resistant to anti-mycobacterial treatment and finally died due to sepsis-related complications.