Association of FADS2 polymorphism rs174538 with fatty acid metabolism and disease severity in Japanese patients with Crohn’s disease

BACKGROUND Crohn’s disease (CD) is a chronic inflammatory bowel disease with unknown etiology. Inflammatory chemical mediators synthesized from arachidonic acid, an n-6 polyunsaturated fatty acid (PUFA), have been shown to activate CD. Additionally, n-3 PUFAs are metabolized by the same enzyme as n-6 PUFAs and known to inhibit the arachidonic acid cascade. Our previous study noted that the presence of erythrocyte membrane fatty acids is a characteristic finding in Japanese CD patients. It was thus speculated that FADS2 gene polymorphisms, which induce PUFA metabolizing enzymes, are involved in the pathogenesis of CD, though no such relationship was found. AIM To investigate the relationship of FADS2 polymorphisms with serum and erythrocyte membrane fatty acid composition ratios, and disease activity. METHODS Using previously reported findings regarding FADS2 genetic polymorphisms, the records of 52 CD patients undergoing treatment at Jikei University Kashiwa Hospital were analyzed. Mutations noted were divided into three groups; wild -type (GG ), heterozygous mutants (GA ), and homozygous (AA ), with the activities of delta-6 and delta-5 desaturases compared using redefined d6d index (rd.d6di) and d5d index (d5di). Additionally, comparisons of serum and erythrocyte membranes for fatty acid composition, and also gene polymorphisms and CD activity index (CDAI) were performed. RESULTS The presence of the rs174538 mutation in FADS2 resulted in reduction of only rd.d6di in the erythrocyte membrane (P < 0.01). In contrast, that mutation was found to be associated with d5di induced by FADS1 in serum (P = 0.019) as well as the erythrocyte membrane (P < 0.0001), and also with reduction in the fatty acid composition of arachidonic acid in both serum (P < 0.0001) and the erythrocyte membrane (P < 0.01). Regarding disease activity, a positive correlation of CDAI score with rd.d6di in both serum (P < 0.05) and the erythrocyte membrane (P < 0.05) was found only in the rs174538 wild -type group. In contrast, there was no correction between CDAI and d5di in either serum or erythrocyte membrane samples. CONCLUSION The rs174538 mutation alters the fatty acid profile through strong linkage to the FADS1 gene. In wild -type individuals, rd.d6di was positively correlated with CDAI, suggesting predictive utility of disease severity.