# Genetic Variants of the ATIC Gene and Therapeutic Response to Methotrexate in Patients with Rheumatoid Arthritis

## TL;DR

This study finds that a specific genetic variant in the ATIC gene is linked to poor response to methotrexate in rheumatoid arthritis patients.

## Contribution

The study identifies rs4673993 as a novel genetic variant associated with methotrexate resistance in rheumatoid arthritis.

## Key findings

- Patients with the rs4673993 homozygous variant had a 4.5-fold higher risk of non-response to methotrexate.
- Non-responders had significantly higher IL-6 levels compared to responders.
- Sulfasalazine use was associated with protective effects against methotrexate resistance.

## Abstract

Methotrexate (MTX) is the conventional synthetic disease-modifying anti-rheumatic drug (csDMARD) recommended as the first-choice anti-rheumatic drug for rheumatoid arthritis (RA). However, responses to MTX may be influenced by genetic variants. We aim to evaluate the association of the rs2372536, rs4673990, and rs4673993 genetic variants of the ATIC gene with therapeutic failure of MTX in patients with RA. A case–control study was performed. Disease activity was measured using the disease activity score based on erythrocyte sedimentation rate (DAS28-ESR). RA patients were classified into two groups: (a) responders (DAS28-ESR ≤ 3.2), which is the group of patients who did respond to methotrexate, and (b) non-responders (DAS28-ESR > 3.2), which is the group of patients who did not respond to methotrexate. Serum levels of the 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) enzyme and Interleukin-6 (IL-6) were quantified using an enzyme-linked immunosorbent assay (ELISA). Genotyping of ATIC genetic variants was performed with quantitative polymerase chain reaction (qPCR) using TaqMan probes. A total of 260 patients with RA were included. In total, 142 (54.6%) were non-responders to MTX. IL-6 levels were increased in the non-responder group (p = 0.002), while no statistical differences were observed in the AICAR levels. The variables associated with non-response were higher HAQ-Di, weekly MTX dose, glucocorticoid use, erythrocyte sedimentation rate, and carriers of the polymorphic homozygous variant of rs4673993 (OR = 4.5, 95% CI: 1.04–19.34; p = 0.04). The use of sulfazaline offered protective effects. Our findings indicate that the polymorphism rs4673993 gene variant of the AICAR protein may significantly influence MTX resistance. Therefore, these results support the importance of the pathway generating extracellular adenosine and its effects on promoting the immune regulation for the mechanism of MTX therapy of RA.