Autosomal recessive (AR) complete STAT1 deficiency, reported in 24 patients from 15 kindreds (10, 11), was described in 2003 as underlying severe viral infections due to impaired type I and III IFN signaling and of mycobacterial disease due to impaired type II IFN signaling (10, 12, 13). Here, STAT1 is linked to viral infectious disease.