TNF polymorphisms in psoriasis: association of psoriatic arthritis with the promoter polymorphism TNF*-857 independent of the PSORS1 risk allele.

OBJECTIVE

Single-nucleotide polymorphisms (SNPs) of the tumor necrosis factor gene TNF at positions -238 and -308 have been associated with psoriasis vulgaris and psoriatic arthritis (PsA). The strong linkage disequilibrium (LD) at chromosome region 6p21, a region known to harbor risk factors for psoriasis susceptibility (PSORS1) other than just SNPs of the TNF gene, renders the interpretation of these findings difficult. The aim of this study was to analyze several SNPs of the TNF gene and its neighboring LTA gene for independent and dependent carriage of the PSORS1 risk allele.

METHODS

SNPs in the promoter of the TNF (-238G/A, -308G/A, -857C/T, and -1031T/C), LTA (+252A/G), TNLFRSF1A (+36A/G), and TNLFRSF1B (+676T/G) genes were genotyped in 375 psoriasis patients, 375 PsA patients, and 376 controls. The Trp- Trp-Cys-Cys haplotype of the CCHCR1 gene (CCHCR1*WWCC) was used as an estimate of the risk allele PSORS1.

RESULTS

Whereas we were able to confirm the previously described strong association of allele TNF*-238A with psoriasis, our study revealed that this association was completely dependent on carriage of the PSORS1 risk allele. For PsA, but not psoriasis vulgaris without joint involvement, a strong association with the allele TNF*-857T (odds ratio 1.956 [95% confidence interval 1.334-2.881]; corrected P = 0.0025) was also detected in patients negative for the PSORS1 risk allele.

CONCLUSION

Our results indicate that there are genetic differences between psoriasis vulgaris patients with and without joint manifestations. While the previously reported association between TNF*-238A and psoriasis seems to primarily reflect LD with PSORS1, TNF*-857T may represent a risk factor for PsA that is independent of the PSORS1 allele.