Disease association of two distinct interleukin-18 promoter polymorphisms in Caucasian rheumatoid arthritis patients

Interleukin (IL)-18 is an important mediator of innate and adaptive immunity. We searched for an association of IL-18 promoter single-nucleotide polymorphisms (SNP) with rheumatoid arthritis (RA) in Caucasians. The entire study population was composed of two independent cohorts from Germany (n=200) and Scotland (n=410). Presence of IL-18 SNP at positions -607 and -137 was determined by allele-specific PCR in 327 RA patients and 283 healthy donors (HD). Diplotype distributions of both loci were in Hardy-Weinberg equilibrium (HWE) in the German and Scottish HD cohorts. In contrast, locus -607 was in HW disequilibrium in German, and locus -137 in Scottish RA patients. Diplotypic exact chi(2) tests suggested that -607CC was overrepresented in German, and -137CC in Scottish RA patients, but conservative chi(2) trend analyses could not prove any significant disease association of these single loci. SNP -607 and -137 were in strong linkage disequilibrium. The -607C(*)-137C haplotype was more prevalent in German RA (3.2 vs 1.2%) and in Scottish RA patients (4.1 vs 0.9%) than in the respective HD cohorts. These observations suggest that SNP of both positions contribute to the genetic background of RA pathogenesis.