Severe eosinophilia (>5.0 × 109/L) was reported in Omenn syndrome, Wiskott Aldrich syndrome, ADA deficiency, autoimmune lymphoproliferative syndrome, immunodysregulation polyendocrinopathy enteropathy X-linked, STAT3 deficiency, DOCK8 deficiency, CD40 deficiency, MHC II deficiency, Kostmann disease, Papillon-Lefevre syndrome, and CVID. Here, STAT3 is linked to immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.