Genome-wide association (GWA) studies have discovered some IBD susceptibility genes in interleukin-23/T-helper 17 (IL-23/Th17) pathway, such as IL-12B, IL-23R, Janus kinase 2 gene (JAK2), signal transducer and activator of transcription 3 (STAT3) and tumor necrosis factor (ligand) superfamily member 15 (TNFSF15) [2–5]. Here, IL23A is linked to inflammatory bowel disease.