Epistatic interaction between TLR4 and NOD2 in patients with Crohn's Disease: relation with risk and phenotype in a Spanish cohort

Crohn's Disease is one of the two major forms of the Inflammatory Bowel Diseases and, although the etiology is not completely understood, the confluence of environmental and genetic factors has been demonstrated. The aim of this study was to determine the distribution of TLR4 variants in a Spanish cohort of Crohn's Disease patients and their relation with phenotype and common NOD2 variants. A total of 371 Crohn's Disease (CD) patients and 636 healthy controls (HC) were included. Single Nucleotide Polimorphisms (SNPs) in TLR4 (D299G and T399I) and NOD2 (R702W and G908R) detection was performed by a Taqman® Allelic Discrimination Assay. 1007insC NOD2 variant was analyzed using a PCR combined with fluorescent technology and the different alleles were determined depending on the PCR products size. D299G and T399I were related to CD only in patients carrying NOD2 variants (NOD2+/TLR4+ haplotype) (p = 0.036; OR = 1.924), increasing the risk to develop CD when 1007insC and TLR4 variants were both present (OR = 4.886). We also described a strong association between mutant NOD2 and CD risk (p < 0.001, OR = 3.214). R702W, G908R and 1007insC were associated when they were considered separately (p < 0.001; p = 0.002; p < 0.001, respectively). Moreover, the patients carrying any mutant D299 G or T399I polymorphisms were predisposed to develop a stricturing disease (p = 0.013; OR = 2.391), especially in the presence of NOD2 mutation (p = 0.002; OR = 4.989). In this study, ileal disease was also associated with the presence of at least one NOD2 susceptibility allele (p = 0.001; OR = 3.838) and, the risk of ileal CD was increased if TLR4 variants were presents (p < 0.050; OR = 4.160). TLR4 variants were related to bowel perforation, independently of NOD2.