The Child with Recurrent Mycobacterial Disease

Many genetic conditions predispose affected individuals to opportunistic infections. A number of immunodeficiency diseases, including genetic defects termed Mendelian susceptibility to mycobacterial disease (MSMD), permit infection from many different strains of mycobacteria that would otherwise not cause disease. These include tuberculous and nontuberculous mycobacteria, and bacille Calmette-Guérin vaccine (BCG). Patients may present with infections from other organisms that depend on macrophage function for containment. Defects in multiple genes in the IL-12 and NFKB signaling pathways can cause the MSMD phenotype, some of which include IL12RB1, IL12B, IKBKG, ISG15, IFNGR1, IFNGR2, CYBB, TYK2, IRF8, and STAT1.

Multiple autosomal recessive and dominant, and 2 X-linked recessive gene defects resulting in the MSMD phenotype have been reported, and others await discovery. This review presents the known gene defects and describes clinical findings that result from the mutations. If MSMD is suspected, a careful clinical history and examination and basic immunodeficiency screening tests will narrow the differential diagnosis. A specific diagnosis requires more sophisticated laboratory investigation. Genetic testing permits a definitive diagnosis, permitting genetic counseling. Mild cases respond well to appropriate antibiotic therapy, whereas severe disease may require hematopoietic stem cell transplantation.