Janus kinase 1 (JAK1) is one of the most important kinases downstream of IFN-I, and the JAK1 gain-of-function variant A634D was reported to cause a syndrome characterized by hepatosplenomegaly, eosinophilia, enteritis, thyroid disease, growth retardation, and susceptibility to viral infection [65, 66]. The gene discussed is JAK1; the disease is Increased total eosinophil count.