Genome-wide association studies (GWAS) and large cohort studies demonstrated that IL23R[3], [5], [6], [7] and additional genes involved in Th17 differentiation (e.g., IL12B, JAK2, TYK2, STAT3, CCR6, IL2/IL21 and TNFSF15) are associated with the susceptibility to Crohn's disease (CD) and partly also to ulcerative colitis (UC) [5], [8], [9], [10], [11]. Here, IL12B is linked to Crohn disease.