Tumor necrosis factor (TNF)-α gene +489 polymorphisms: association with psoriatic arthritis

Objective of this work was to investigate the role of single nucleotide polymorphisms (SNPs) at position +489 of the tumor necrosis factor (TNF)-α gene in generic susceptibility and severity of psoriatic arthritis (PsA). Fifty-seven Caucasian PsA patients diagnosed according to CASPAR criteria and 155 healthy matched controls were studied. PASI score, DAS28 and Disability INdex HAQ were calculated. Genomic DNA was extracted from peripheral blood samples and SNPs +489 G>A (rs 80267959) were amplified by PCR. The SNP +489 genotype was significantly associated with PsA susceptibility (p=0.0136) and severity of clinical and laboratory parameters (p values ranging from 0.016 to 2.908 x 10-12). The difference in severity was accounted for by the difference between the AA and GA genotypes with respect to the GG genotype. These findings suggest that TNF-α gene polymorphisms may influence PsA susceptibility and severity. Psoriatics arthritis (PsA) is a complex immunemediated disease that results from the interplay between multiple genetic and environmental factor [1]. Although the pathogenesis of PsA remains elusive, there is evidence that genetic factors may contribute to the etiology of the disease [2]. Is has been estimated that at least one third of the genetic contribution to PsA resides in the major histocompatibility complex (MHC) region [2]. The tumor necrosis factor (TNF)-α gene, which is located in the short arm of chromosome 6 in the MHC class III region between the HLA-B and HLA-DR genes, has been proposed as a major candidate gene in PsA [3]. This hypothesis is supported by studies which have found high serum, synovial fluid and synovial membrane TNF-α levels in patients with PsA [4,5]. Several single nucleotide polymorphisms (PNPs) have been identified in the TNF-α gene promoter [6]. In particular, two common polymorphisms, namely G to A substitutions at positions -238 and -308 have been studied in patients with PsA. However, association studies of these two TNF-α polymorphisms and genetic susceptibility to PsA have lead to conflicting results [7-12]. Previous studies have indicated the potential role of the SNP at +489 position in the first intron of the TNF-α gene in the susceptibility to some rheumatic autoimmune diseases like rheumatoid arthritis [13], systemic lupus erythematosus [14] and systemic sclerosis [15]. However, to our present knowledge, studies on the association of +489 polymorphism with PsA susceptibility and response to TNF-α inhibitors are not reported in the literature. Is this study we investigated the role of SNPs at +489 within the TNF-α gene in PsA susceptibility and severity.