Polymorphisms of the folate metabolizing enzymes: Association with SLE susceptibility and in silico analysis.

Systemic lupus erythematosus (SLE) is a typical autoimmune disorder with multiple organ involvement and unknown etiology. It has been shown that polymorphic variants of the genes encoding key enzymes of folate and methionine metabolism may influence DNA methylation. Genomic DNA was extracted from blood samples of 150 SLE patients and 160 controls, matching age, sex, and ethnicity. MTHFR rs1801133C>T and MTR rs1805087A>G polymorphisms were genotyped by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. MTHFR rs1801131A>C genotype was determined by the tetra-primer amplification refractory mutation system (Tetra-ARMS), and DHFR rs70991108 polymorphisms' genotyping was performed by PCR methods. In-silico approach was used to analyses the effects of these variations on the structure of mRNA and protein. MTHFR rs1801131AC+CC genotypes were significantly higher in the SLE patients compared to the controls (37 vs. 26%, OR 1.7 (95% CI 1-2.8); p=0.03). The frequency of MTHFR rs1801131C allele was significantly higher in the SLE patients than the controls (22 vs. 15%, p=0.02). However, there was no association between MTHFR rs1801133C>T polymorphism and SLE. The frequency of CT haplotype of MTHFR rs1801133C>T and rs1801131A>C polymorphisms was significantly higher in the SLE patients (20 vs. 12%), and CT haplotype may be potentially a risk factor for SLE susceptibility [OR 1.9 (95% CI 1.2-2.9); p=0.006]. There was no association between alleles and genotypes of DHFR rs70991108 polymorphism and SLE susceptibility. The frequency of MTR rs1805087AG genotype was less frequent in the SLE patients compared to the controls, and this genotype could decrease the SLE risk (35 vs. 48%), (OR, 0.6 (95% CI, 0.4 to 0.9), p=0.03). In silico-analysis showed that both of MTHFR rs1801133C>T and rs1801131A>C SNPs made fundamental changes in the secondary structure of MTHFR-mRNA (p=0.0412 and p=0.1641; p<0.2). Also, structural analysis of the rs1801131A>C variation showed a significant effect on MTHFR function. Bioinformatics analysis showed that rs70991108 polymorphism in DHFR gene would lead to a significant alteration of the splicing process. In conclusion, MTHFR rs1801131 AC+CC genotypes could be a risk factor and MTR rs1805087AG genotype could be a protective factor for SLE susceptibility. There was no association between MTHFR rs1801133C>T and DHFR rs70991108 polymorphisms and SLE.