Association study of MICA gene polymorphisms with rheumatoid arthritis susceptibility in south Tunisian population.

The aim of this study was to investigate the role of major histocompatibility complex (MHC) class I chain-related gene A (MICA) polymorphisms, important in natural killer (NK) cell function, in patients with rheumatoid arthritis (RA). A transmembrane (TM) alanine-encoding GCT repeats, termed A4, A5, A5.1, A6 and A9 in the MICA gene, and single-nucleotide polymorphisms (SNPs): the Met129Val polymorphism (rs1051792) and the nonsynonymously coding SNP (rs1051794) were genotyped in 142 patients with RA and 123 unrelated healthy individuals using, respectively, PCR fluorescent method, nested PCR-RFLP and allele specific PCR (ASP). Association was assessed based on the χ2 test, genotype relative risk (GRR) and odds ratio (OR) with 95% confidence intervals (CIs). Our results show a trend of association of the different MICA genotypes G/G, G/A and A/A (P = 0.029) which did not attain the significance after Bonferroni's correction (pc = 0.08). Although, we revealed a significant association of the genotype A/A of MICA-250 in patients with RA compared to healthy controls (pc = 0.033). In contrast, no significant differences between alleles and genotypes frequencies were found either with MICA-TM or MICA met129 val (P > 0.05) in our sample. Moreover, stratification of patients with RA according to clinical and immunological data for the different polymorphisms studied shows a significant association of both MICA-250 G allele (pc = 0.0075) and MICA-250 GG genotype (pc = 0.008) and both allelic (val) (pc = 0.021) and genotypic (val/val) distribution (pc = 0.0095) for MICA met129 val in the RF-positive subgroup compared to RF-negative patients with RA. In contrast, we found a strong association of the MICA-TM A9 allele in RF-negative patients with RA (pc = 0.0003). This study indicates the involvement of the MICA-250 polymorphism in the genetic susceptibility and severity to RA and suggests that variations in MICA-TM and MICA met129 val may have an effect on RA severity in our south Tunisian sample.

Association study of CARD8 (p.C10X) and NLRP3 (p.Q705K) variants with rheumatoid arthritis in French and Tunisian populations.

The objective of the study was to investigate the association of caspase activating and recruitment domain 8 (CARD8) and nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain containing 3 (NLRP3) polymorphisms with rheumatoid arthritis (RA) in Tunisian and French populations. CARD8 (c.30T>A, rs2043211) and NLRP3 (c.2113C>A, rs35829419) single nucleotide polymorphisms (SNPs) were genotyped in 100 French RA trio families and 141 Tunisian patients with RA and 191 unrelated healthy controls, using TaqMan(®) allelic discrimination assay. The genetic analyses for the association and linkage in French families were performed using the comparison of allelic frequencies (AFBAC), the genotype relative risk (GRR) and the transmission disequilibrium test (TDT). Data for case and control samples were analysed by chi-square-test, GRR and odds ratio (OR). No significant differences between alleles and genotypes frequencies were detected in French trio and Tunisian patients with RA and controls, either with CARD8 or with NLRP3 SNPs both in French and in Tunisian populations. Moreover, stratifying patients according to the presence of rheumatoid factor (RF), anti-cyclic peptides antibodies (ACPA), erosion, nodules, other autoimmune disease or HLA-DRB1*04-positive subgroups did not show any significant association with CARD8 or NLRP3 (P ≥ 0.05). This study suggests that variations in the innate immunity genes CARD8 (p.C10X) and NLRP3 (p.Q705K) have no effect on RA susceptibility either in the Tunisian or in the French population.

Signal transducer and activator of transcription and the risk of rheumatoid arthritis and thyroid autoimmune disorders.

OBJECTIVES: The signal transducer and activator of transcription 4 (STAT4) gene localised on chromosome 2q32.2-q32.3 is known to be essential for mediating responses to interleukin 12 in lymphocytes and regulating the differentiation of T helper cells. The aim of this study was to investigate the role of the STAT4 gene in susceptibility to rheumatoid arthritis (RA) and autoimmune thyroid diseases (AITDs) in Tunisian case control studies. METHODS: Genotyping of STAT4 rs7574865 single nucleotide polymorphism (SNP) was performed in 140 patients affected with RA, 159 patients affected with AITDs and 200 healthy controls using TaqMan® allelic discrimination assay. Data were analysed by χ2-test, genotype relative risk (GRR) and odds ratio (OR). RESULTS: Our results revealed that frequencies of the T allele and the T/T genotype were significantly higher among RA patients compared to controls (p=0.008; p=0.003, respectively). However, no significant associations with the risk of autoimmune thyroid diseases were detected. Moreover, the stratification of RA patients subgroups revealed a significant association of both T allele and T/T genotype in patients presented erosion (p=0.003; p=0.004, respectively) as well as anti-cyclic peptides-negative RA (ACPA-) (p=0.002; p=0.0003, respectively). Furthermore, genotypic association was found according to the absence of rheumatoid factor antibody (RF) (p=0.0014). But, no significant differences in allele and genotype frequencies of STAT4 rs7574865 polymorphism were detected according to the presence of another autoimmune disease, nodules and in HLA-DRB1*04 and HLA-DRB1*0404 positive subgroups. CONCLUSIONS: Our results support involvement of the STAT4 gene in the genetic susceptibility to RA but not to AITDs in the Tunisian population.