Interleukin-18-promoter polymorphisms are not relevant in rheumatoid arthritis.

Interleukin-18 (IL-18), a member of the IL-1 family, is known to play a relevant role in rheumatoid arthritis (RA) physiopathology mainly by promoting the inflammatory response. The aim of this work was to investigate the possible implication of two single-nucleotide polymorphisms (SNPs) [-607 A/C (rs1946518) and -137 G/C (rs187238)] within the IL-18-promoter region in RA predisposition and clinical course. A total of 362 unrelated RA patients and 339 healthy controls were genotyped using a real-time polymerase chain reaction (PCR) method for the -607 A/C SNP and a sequence-specific PCR method (PCR-SSP) for the -137 G/C polymorphism. No statistically significant differences were observed for both -607 and -137 IL-18-promoter polymorphisms between RA patients and controls, considering either allelic or genotypic frequencies. In addition, no association was found with the haplotypes inferred by the two polymorphisms and RA susceptibility. This was also the case when RA patients were stratified according to sex, age at the onset of the disease, rheumatoid factor status, and extraarticular manifestations. Our data suggest that -607 A/C (rs1946518) and -137 G/C (rs187238) polymorphisms within the IL-18-promoter region do not play a major role in RA predisposition.