Association between non-coding transcript variant polymorphisms (rs3135499, rs3135500) of the NOD2 gene and the propensity to rheumatoid arthritis in the Iraqi population

Aim

The objective of this study was to explore how the existence of two particular SNPs located in potential binding sites for microRNAs in the 3′- UTR region of the NOD2 gene could impact the susceptibility to rheumatoid arthritis (RA) among the Iraqi population.

Background

Rheumatoid arthritis (RA) is a chronic autoimmune condition that predominantly affects the joints. In RA, the immune system erroneously attacks the tissue surrounding the joints, resulting in stiffness, inflammation, pain, and mobility restrictions, particularly in areas such as the wrists, spine, knees, ankles, and feet. While numerous genes in the human genome play a part in the development of RA, specific genetic regions within these genes may have a noteworthy influence on both the initiation and progression of RA and this influence may extend to other inflammatory conditions as well.

Method

In a case-control study, genomic DNA (gDNA) was isolated from the peripheral blood of 200 individuals. These participants were categorized into two groups: one comprising 100 individuals diagnosed with rheumatoid arthritis, and the other composed of 100 healthy individuals who served as the control group. Various laboratory parameters and anthropometric data, such as age, gender, body mass index (BMI), levels of anti-cyclic citrullinated peptide (anti-CCP), and rheumatoid factor (RF), were assessed. Subsequently, all samples were genotyped for two specific polymorphisms located within the NOD2 gene (rs3135499 and rs3135500) using rhAmp-polymerase chain reaction technology. Finally, the collected data underwent analysis using a range of statistical methods.

Results

The results indicated a substantial correlation between the risk of developing rheumatoid arthritis (RA) and the allele frequencies of the rs3135500G > A polymorphism, specifically [G vs A; Odds Ratio (OR) = 1.76; 95% Confidence Interval (CI) (1.8 – –2.6); p < 0.005], as well as the genotypes [GG vs GA + AA; OR = 2.4; 95% CI (1.15–2.2), p < 0.001], [GA vs GG; OR = 0.1; 95% CI (0.33–0.4), p < 0.001], and [AA vs GG; OR = 0.08; 95% CI (0.02–0.37), p < 0.001]. Conversely, the rs3135499 A > C polymorphism did not exhibit significant variations, except for [CC vs AA+AC; OR = 2.7; 95% CI (1.3–5.73), p < 0.009], and [AC vs AA; OR = 2.95; 95% CI (0.87–10.02), p < 0.03] after adjusting for factors like gender, age, BMI, smoking status, and family history. It's worth noting that markers such as anti-CCP, RF, and CRP produced positive results exclusively among RA patients. Additionally, parameters like BMI, ESR, WBCs, and Urea exhibited significant differences between the RA group and the healthy control group (p < 0.02, p < 0.0001, p < 0.002, and p < 0.01, respectively). Furthermore, there was a strong linkage observed between the rs3135500G > A and rs3135499A > C polymorphism of the NOD2 gene in patients (D′ = 0.85).

Conclusion

Our findings indicate an association between rheumatoid arthritis (RA) and the rs3135500 G/A polymorphism situated in the 3′-UTR of the NOD2 gene, particularly in the presence of the A allele. Additionally, the AA haplotype model was associated with an increased susceptibility to RA within the genetic region of NOD2.