TNF and Crohn disease: In agreement with previous studies in which arachidonic acid and FADS2 were found to be related to Crohn’s disease [52, 53], our data from a population-based cohort systematically revealed (1) the association between FADS2 and arachidonic acid, (2) the association between the arachidonic acid pathway and immune phenotypes, and (3) the association between FADS2 and immune phenotypes (i.e., TNFα).