The impact of gene polymorphisms on the response of methotrexate-based treatments.

Methotrexate (MTX) is a long-standing drug used to treat leukemia (at high doses to inhibit DNA/RNA synthesis) and rheumatoid arthritis (at low doses for anti-inflammatory effects). Its characteristic narrow therapeutic range, in terms of efficacy and safety associated with MTX, are important factors to consider when deciding whether to prescribe it. A major challenge in its use is interindividual variability which is largely attributed to germline genetic polymorphisms in genes encoding proteins that control the pharmacokinetics or pharmacodynamics of MTX. This study updates a previous 2018 review using a systematic literature search in PubMed/MEDLINE, Scopus, and SciELO. The search, conducted according to the PRISMA protocol, employed predefined keywords to identify studies published up to June 2025. This systematic review identified that, to date, only a few genetic polymorphisms influence clinical decision-making. Specifically, the MTHFR 677T allele and the MTHFR 677T-1298 A haplotype (rs1801133- rs1801131) have been associated with toxicity in both adults and children. Furthermore, the 677T-1298 A haplotype has been linked with reduced event-free survival in Caucasian patients with either adult RA or pediatric ALL. Regarding other markers, the TYMS rs34743033 3R allele has been implicated with reduced efficacy in adult patients receiving low-dose MTX, while the FPGS rs1544105 T allele has shown an association with diverse toxicities in ALL pediatric patients. Although considerable research has been conducted and numerous results have been obtained, the available evidence remains predominantly of moderate quality. Consequently, current guidelines from CPIC and the DPWG do not recommend routine MTX dose adjustments based solely on single gene variants. It is, therefore, imperative to develop and validate multifactorial risk prediction tools that integrate a range of other clinical factors. Accordingly, the establishment of a comprehensive pharmacogenetics-guided dosing guideline for MTX remains an elusive goal.