Detailed assessment of NOD2/CARD15 exonic variation in inflammatory bowel disease in Scotland: implications for disease pathogenesis.

The high incidence of Scottish Crohn's disease (CD) is not explained by the common three NOD2/CARD15 variants. We aimed to identify population-specific NOD2/CARD15 coding variants. A total of 1478 (320 inflammatory bowel disease patients <16 years, 343 adult CD patients, 542 parents and 273 controls). All NOD2/CARD15 exons were sequenced in 24 CD patients. Sequencing identified 18 single-nucleotide polymorphisms (SNPs) including 4 non-synonymous coding SNPs altering the structure of the Leucine-rich region--two were well established (1007-/C and 908G/R). Two other variants, valine955isoleucine (955V/I) and methionine863valine (863M/V), were genotyped in all subjects. 863M/V carriage was not significantly higher in CD patients vs controls (1.35 vs 0.37%, P=0.27). 955V/I carriage was no higher in CD or ulcerative colitis patients (12.8 and 15.8%, respectively) compared to controls (16.2%). Transmission disequilibrium test analysis was negative. 955V/I carriage was higher in indeterminate colitis patients (n=29) compared to controls (41.4 vs 16.2%, P=0.001, OR=3.6 (1.6-8.2)). Population-specific NOD2/CARD15 exonic variants do not account for the high-CD prevalence in Scotland.