The coding regions of the five genes known to be associated with MSMD (IL12B, IL12RB1, IFNGR1, IFNGR2, and STAT1) were sequenced following amplification of the corresponding cDNAs from Epstein-Barr virus (EBV)–transformed B cells from the patients. This evidence concerns the gene IFNGR2 and Mendelian susceptibility to mycobacterial diseases.