Previous research showed that the SLC22A4 variant, as an inflammation-related gene polymorphism involved in the innate immune response, is significantly correlated with an increased susceptibility to inflammatory bowel disease (IBD), Crohn's disease (CD) and ulcerative colitis (UC) by changing the transcription and function of organic cation transporters [39–41]. Here, SLC22A4 is linked to Crohn disease.