Activation of IFN signaling in response to viral infection triggers a signal transduction cascade involving Janus kinase (JAK) and signal transducer and activator of transcription (STAT) proteins, culminating in the nuclear translocation of the transcription factor complex ISGF3 (IFN-stimulated gene factor 3), comprising IFN-regulatory factor 9 (IRF9) and phosphorylated STAT1 and STAT2 [2,3]. The gene discussed is IRF9; the disease is viral infectious disease.