Molecular expression and single nucleotide polymorphisms of the IL17A gene among etanercept-treated rheumatoid arthritis patients

Molecular expression (reverse transcription-quantitative polymerase chain reaction; RT-qPCR) and DNA-sequencing-based single nucleotide polymorphisms (SNPs) of interleukin 17A (IL17A) gene were determined in 51 etanercept-treated Iraqi rheumatoid arthritis (RA) patients and 45 control. The results revealed that the relative expression (2-∆∆Ct) of the IL17A gene was increased by 1.28 ± 0.29 fold in RA patients, and such profile was approximated in males (1.66 ± 0.58) and female (1.01 ± 0.28) patients.  Concerning PCR-amplified DNA sequences, out of the 10 encountered SNPs, two SNPs (rs8193038 and rs3819025) showed allele frequencies that exceeded 10%. The rs8193038 SNP allele and genotype frequencies showed no significant variations between RA patients and control. The second SNP (rs3819025) was observed to have three genotypes (AA, AG, and GG). Among these genotypes, it was observed that the homozygous genotype of the mutant allele (GG) was only recorded in patients with a frequency of 13.7%, while none of the control had this genotype. Such a difference was significant even after the correction of probability (pc = 0.05), and the associated OR was 15.34 (95% C.I.: 1.39 - 169.24). It was also observed that G allele showed a significant increased frequency in patients (25.5 vs. 12.2%; OR = 2.46; 95% C.I.: 1.14 - 5.30; p = 0.015), while A allele frequency was significantly decreased (74.5 vs. 87.8%; OR = 0.41; 95% C.I.: 0.19 - 0.88; p = 0.015). However, the significance in both cases was lost when the probability was corrected.  It was also observed that there was no significant impact of the rs3819025 SNP genotypes on the expression of the IL17A gene. In conclusion, the IL17A gene showed an increased expression in RA patients, and rs3024419 SNP is suggested to be associated with an increased risk to develop the disease in the Iraqi population.