MAG12 genetic variation and inflammatory bowel disease

Background: Despite recent advances the majority of inflammatory bowel disease (IBD) susceptibility 'genes' remain undiscovered. Recent data suggest that autoimmune conditions may 'share' susceptibility loci. Epidemiological evidence indicates an association between celiac disease and IBD and both conditions demonstrate increased gut permeability. MAGI2, recently implicated in ulcerative colitis (UC) and celiac disease, encodes a scaffolding protein involved in epithelial integrity. Our aim was to test MAGI2 variants for association with IBD and also their role in determining intermediate hereditary phenotypes defined by antibody production to microbial antigens. Methods: We genotyped 113 MAGI2 single nucleotide polymorphisms (SNPs) in 681 cases of Crohn's disease (CD), 259 UC cases, and 195 controls. Results: The most significant IBD association was in intron 6 (rs2160322, P = 0.009) and both UC (P = 0.006) and CD (P = 0.03) contributed to this association. The most significant CD association was with an intron 2 haplotype (rs7785088/rs323149/rs13246026, P = 0.002). We observed highly significant associations with UC in intron 6 (rs7803276/rs7803705, P = 0.002) and also significant associations in introns 2, 6, and 20. Significant associations were seen with: immunoglobulin G (IgG) anti-Saccharomyces cerevisiae antibodies (ASCA)-positive CD in intron 3 (P = 0.003), intron 6 (P = 0.003), and intron 20 (P = 0.001); anti-CBir1-positive CD in intron 3 (P = 0.0001) and intron 6 (P = 0.008); and anti-outer membrane porin C (OmpC)-positive CD in intron 3 (P = 0.0009), and intron 9 (P = 0.007). Quantitative antibody levels were also associated with variants in intron 4 (anti- IgA ASCA, P = 0.0003 and anti-IgG ASCA, P = 0.0002). Conclusions: These findings support the significance of the epithelial barrier in IBD pathogenesis.