Association of hyperhomocysteinemia with genetic variants in key enzymes of homocysteine metabolism and methotrexate toxicity in rheumatoid arthritis patients.

OBJECTIVES: The study investigated the association between plasma homocysteine, folate and vitamin B12 with 5,10 methylenetetrahydrofolate reductase (MTHFR C677T and A1298C), thymidylate synthase (TYMS 2R â†’ 3R) and methionine synthase (MTR A2756G) polymorphisms and methotrexate (MTX) treatment and toxicity in Tunisian Rheumatoid arthritis (RA) patients. METHODS: A total of 185 patients with RA were included. Homocysteine (Hcy) was assessed by fluorescence polarization immunoassay, and folate and vitamin B12 were measured by chemiluminescence immunoassays. The genetic polymorphisms were analyzed by PCR or PCR-RFLP. Hyperhomocysteinemia (HHC) was considered for Hcy > 15 µmol/L. RESULTS: MTHFR C677T polymorphism was associated with HHC in RA patients (multi-adjusted OR, 95% CI 2.18, [1.07-4.57]; p = 0.031). No association was detected with the remaining polymorphisms. Plasma Hcy, folate, and vitamin B12 did not differ according to each polymorphism, or with MTX treatment or toxicity. However, HHC was more prevalent in patients with than those without MTX toxicity (32.7 vs. 16.7%; p = 0.035). CONCLUSIONS: The MTHFR 677TT genotype is an independent risk factor for HHC in Tunisians RA patients. HHC could be a useful marker of MTX toxicity in RA patients.

Measurement of absolute copy number variation of Glutathione S-Transferase M1 gene by digital droplet PCR and association analysis in Tunisian Rheumatoid Arthritis population.

BACKGROUND: The investigation of copy number variations (CNVs) analysis of candidate genes is currently an important research area in modulating human diseases. We aimed to quantify CNVs in glutathione S-transferase M1 (GSTM1) gene and determine its genetic contribution in Tunisian rheumatoid arthritis (RA) and its subsets through an innovative technique for quantification. METHODS: A total of 165 RA cases and 102 healthy controls were included in the study. Using a recently powerful approach of digital droplet PCR (ddPCR), we quantified GSTM1 gene to determine the presence of no, one, or multiple copy number (CN) at high levels of sensitivity and specificity. Odds ratio and Fisher exact test were performed to estimate the association risk for GSTM1CNVs in RA. RESULTS: Copy number identified by ddPCR was 0, 1, and 2 copies per diploid genome. A high frequency of '0' copy was revealed with 54% in RA patients. The deletion ('0' copy) of GSTM1 was found to be a significant risk factor for anti-cyclic citrullinated peptide (anti-CCP) positive RA (OR=4.16, CI95% =[1.17-14.7]). In addition, a lack of association was found when comparing between the CNVs of RA patients and those of controls. CONCLUSION: This study highlights the powerful accuracy of ddPCR for the quantification of CNVs and suggests that the variation in the CN of GSTM1 is associated with anti-CCP positivity in RA. However, it does not indicate a specific role in the susceptibility to the disease in our Tunisian sample.

Analysis of two susceptibility SNPs in HLA region and evidence of interaction between rs6457617 in HLA-DQB1 and HLA-DRB1*04 locus on Tunisian rheumatoid arthritis.

Previous genomewide association studies (GWAS) and meta-analyses have enumerated several genes/loci in major histocompatibility complex region, which are consistently associated with rheumatoid arthritis (RA) in different ethnic populations. Given the genetic heterogeneity of the disease, it is necessary to replicate these susceptibility loci in other populations. In this case, we investigate the analysis of two SNPs, rs13192471 and rs6457617, from the human leukocyte antigen (HLA) region with the risk of RA in Tunisian population. These SNPs were previously identified to have a strong RA association signal in several GWAS studies. A case-control sample composed of 142 RA patients and 123 healthy controls was analysed. Genotyping of rs13192471 and rs6457617 was carried out using real-time PCR methods by TaqMan allelic discrimination assay. A trend of significant association was found in rs6457617 TT genotype with susceptibility to RA (P = 0.04, pc = 0.08, OR = 1.73). Moreover, using multivariable analysis, the combination of rs6457617*TT-HLA-DRB1*04+ increased risk of RA (OR = 2.38), which suggest a gene-gene interaction event between rs6457617 located within the HLA-DQB1 and HLA-DRB1. Additionally, haplotypic analysis highlighted a significant association of rs6457617*T-HLA-DRB1*04+ haplotype with susceptibility to RA (P = 0.018, pc = 0.036, OR = 1.72). An evidence of association was shown subsequently in antiCCP+ subgroup with rs6457617 both in T allele and TT genotype (P = 0.01, pc = 0.03, OR = 1.66 and P = 0.008, pc = 0.024, OR = 1.28, respectively). However, no association was shown for rs13192471 polymorphism with susceptibility and severity to RA. This study suggests the involvement of rs6457617 locus as risk variant for susceptibility/severity to RA in Tunisian population. Secondly, it highlights the gene-gene interaction between HLA-DQB1 and HLA-DRB1.

Genetic Determinants of Methotrexate Toxicity in Tunisian Patients with Rheumatoid Arthritis: A Study of Polymorphisms Involved in the MTX Metabolic Pathway.

BACKGROUND AND OBJECTIVE: Methotrexate (MTX) is a disease-modifying anti-rheumatic drug used in the treatment of rheumatoid arthritis (RA). It is the first line drug in the treatment of this disease. However, MTX-related adverse drug reactions (ADRs) are seen in 40 % of the patients. The aim of this study was to determine the impact of six genetic polymorphisms located in five genes encoding proteins involved in the MTX metabolic pathway in Tunisian RA patients and evaluate its association with MTX toxicity. METHODS: Genotyping of 5,10 methylenetetrahydrofolate reductase (MTHFR C677T and A1298C), dihydrofolate reductase (DHFR 19-base pair deletion allele), thymidylate synthase (TYMS 2R/3R), methionine synthase (MTR A2756G) and methionine synthase reductase (MTRR A66G) was performed using PCR and PCR-RFLP method in 141 RA patients treated with MTX. Demographic and clinical characteristics were obtained and ADRs were recorded. Association analyses with regard to MTX toxicity were performed using the χ (2) test, the toxicogenetic risk index (TRI) and the Mann-Whitney U-test. RESULTS: The analysis highlighted a significant association of the T/T genotype of MTHFR C677T polymorphism with increased MTX toxicity. However, the MTHFR A1298C, DHFR 19-base pair deletion allele, MTR A2756G and MTRR A66G polymorphisms were not associated with increased MTX toxicity. The TYMS 2R/3R polymorphism had a protective effect against MTX toxicity. CONCLUSION: The results demonstrated that the C677T polymorphism in the MTHFR gene is associated with MTX toxicity in Tunisian RA patients. In contrast, the TYMS 2R/3R polymorphism is associated with a protective effect against overall MTX toxicity.

Association study of human leukocyte antigen-DRB1 alleles with rheumatoid arthritis in south Tunisian patients.

The aim of this study is to explore relationship between HLA-DRB1 alleles and the susceptibility and clinical features of rheumatoid arthritis (RA) in the south Tunisian population. We studied 142 RA patients and 123 controls matched for age, sex, and ethnicity. HLA-DRB1 genotyping and HLA-DRB1*04 subtypes were performed using polymerase chain reaction/sequence-specific primers. Association was assessed based on the χ (2) test and odds ratio with 95% confidence interval. For multiple comparisons, p value was corrected (p (c)) with Bonferroni test. Two alleles, HLA-DRB1*04 (p=0.045, p(c)=NS) and HLA-DRB1*10 (p=0.021, p(c)=NS), were found to have increased frequencies in RA patients compared to controls. In contrast HLA-DRB1*08 allele was found to have a decreased frequency in patients compared to controls (p=0.044, p(c)=NS). Molecular subtyping of the most prevalent allele (DRB1*04) revealed increased frequencies of HLA-DRB1*04:05 in patients compared to controls (p=0.013, p(c)=NS) whereas HLA-DRB1*04:02 showed a protective effect (p=0.005, p(c)=0.04). Moreover, stratified analyses indicated statistically significant associations between HLA-DRB1*04 allele and anti-cyclic peptides antibodies positivity (ACPA(+)) and rheumatoid factor positivity (RF(+); p(c)=0.03, for both subgroups), HLA-DRBI*10 and ACPA(+) and the presence of another autoimmune disease (p(c)=0.05 and p(c)=0.007, respectively), and HLA-DRB1*04:05 and RF(+) and erosion (p(c)=0.005 and p(c)=0.049; respectively). A significant decrease in the frequency of the DRB1*04:02 allele was observed in patients with ACPA(+) and RF(+) subgroups (p(c)=0.04 and p(c)=0.02, respectively). Our results showed that there was a trend of positive association of HLA-DRB1*04 and HLA-DRB1*10 with RA as such and significant associations with the disease severity in the south Tunisian population.

A Tunisian case-control association study of a 6q polymorphism in rheumatoid arthritis.

Rheumatoid arthritis (RA), the most common autoimmune inflammatory disease of the joints, is a multifactorial disease, involving both genetic and environmental risk factors. TNFAIP3 (tumor necrosis factor, alpha-induced protein 3) gene located in a region of genetic susceptibility in RA is an attractive candidate to be involved in autoimmunity disorders. Our aim was to test the single nucleotide polymorphism rs6920220 located near TNFAIP3 in a case-control study in Tunisian population. The rare allele rs6920220-A was reported to have a risk effect on RA in several genome-wide association studies. Our results revealed a trend of an association of rs6920220-A allele with RA and genotypes containing this allele were in a higher proportion in RA patients than in matched controls. These findings have to be confirmed by a replication in largest RA and control groups of the same ethnic origin. TNFAIP3 gene may have a key role in autoimmunity through its action as a negative regulator of the NF-κB pathway. Further functional investigations are required to understand the mechanism by which this gene is involved in the RA pathogenesis.

The R620W polymorphism of the protein tyrosine phosphatase 22 gene in autoimmune thyroid diseases and rheumatoid arthritis in the Tunisian population.

BACKGROUND: Protein tyrosine phosphatase (PTPN22) is involved in the negative regulation of T-cell responsiveness. The association of a coding variant of the PTPN22 gene (R620W) with a number of autoimmune diseases has been described. AIM: The present study investigated whether PTPN22 gene polymorphism was also involved in the genetic predisposition to autoimmune thyroid diseases (AITDs) and rheumatoid arthritis (RA) in a Tunisian case control study. SUBJECTS AND METHODS: DNA samples from 150 patients affected with RA, 204 patients affected with AITDs and 236 healthy controls were genotyped for PTPN22 R620W polymorphism (1858C/T). Genotyping was performed by the polymerase chain reaction-restriction fragment length polymorphism method. RESULTS: No significant differences in T allele frequency (2.3% in RA patients and 1% in AITDs patients vs 2.6% in controls; p=0.85 and p=0.08, respectively) and in genotype frequencies were detected between RA patients and controls (p=0.15) and between AITDs patients (p=0.11). Stratifying patients affected with AITDs according to their phenotype (Graves' disease and Hashimoto's thyroiditis) and RA patients according to the presence of rheumatoid factor (RF) and antibodies against cyclic citrullinated peptides (ACPA) did not show any significant association with PTPN22 R620W allele (p>0.05). CONCLUSION: Our data suggest that the PTPN22 C1858T single nucleotide polymorphism has no or minor effect on RA and AITDs susceptibility in the Tunisian population.