One study33, regarding IL-18 promoter polymorphisms at positions −137G/C and −607C/A, showed that in the Iranian population, the prevalence of the AA genotype and A allele at position −607C/A, but not at −137G/C, were significantly lower in H. pylori-infected duodenal ulcer patients than in H. pylori-negative subjects. Here, IL18 is linked to duodenal ulcer.