CARD9 and inflammatory bowel disease: First, the occurrence and development of IBD involve genetic factors, including germline genetic background, such as the presence of IBD-causative and/or IBD-associated variants, including rare variants in nucleotide-binding oligomerization domain containing 2 (NOD2), interleukin-23 receptor (IL23R), caspase recruitment domain family member 9 (CARD9), E3 ubiquitin-protein ligase, ring finger protein 186 [RNF186], and adenylate cyclase 7 (ADCY7) [4].