Using singleton WES, 12 heterozygous (monoallelic) mutations in the eight MSMD-causing genes, namely TYK2, ZNFX1, IFNGR1, IL23R, JAK1, IL12B, STAT1 and IL12RB, were detected in six patients. The gene discussed is IL12B; the disease is Mendelian susceptibility to mycobacterial diseases.