YDJC (YdjC chitooligosaccharide deacetylase homolog) is a deacetylase enzyme that catalyzes deacetylation of acetylated carbohydrates 1, with a conserved metal-binding active site coordinating magnesium ions 1. Beyond classical carbohydrate metabolism, YDJC has emerged as a critical immune regulator and disease susceptibility gene. In inflammatory bowel disease (IBD) pathogenesis, YDJC restrains Th1 cell differentiation by directly deacetylating SREBP2, a master regulator of cholesterol biosynthesis; YDJC deficiency promotes CD4+ T-cell proliferation and exacerbates colitis in mice, suggesting cholesterol biosynthesis inhibitors could provide therapeutic benefit 2. YDJC appears on multiple shared genetic susceptibility loci for autoimmune diseases: it is a genome-wide significant locus for both psoriasis and Crohn disease 3, a susceptibility locus for ulcerative colitis 4, and exhibits horizontal pleiotropy with rheumatoid arthritis and blood lipid levels 5. The UBE2L3/YDJC autoimmune risk haplotype increases UBE2L3 expression through YY1-mediated chr22 interactions between the two promoters, strengthening proinflammatory NF-κB signaling 6. These findings establish YDJC as a multifunctional protein linking metabolic enzyme function to immune regulation and autoimmune disease susceptibility.