The study investigated changes in dual-specificity DNA phosphatase (DUSP22) methylation in cell-free DNA as a potential biomarker of rheumatoid arthritis. The research involved 27 patients with rheumatoid arthritis and 18 healthy controls, with DNA methylation determined by pyrosequencing. Rheumatoid arthritis patients had lower DUSP22 cfDNA methylation at a specific promoter region compared to controls (36.7 ± 3.3% for RA vs. 46.9 ± 2.6% for controls). In patients with rheumatoid arthritis, age was associated with a significant decrease in DUSP22 DNA methylation at all sites. Lower DNA methylation was also associated with increased joint space narrowing, suggesting an association with radiographic disease severity. The authors conclude that DUSP22 cfDNA methylation may represent a promising non-invasive biomarker in rheumatoid arthritis, but this hypothesis requires validation in larger and ethnically diverse populations.