As to other DMARDs, Matteson et al. found that ESR did not influence response to HCQ monotherapy [34] but in another study a low baseline CRP was the only predictor of a favorable response to HCQ monotherapy in early RA patients (OR (CRP ≤10 mg/L) = 3.6, 95% CI 2.2 to 6.0) [35]. Here, ESR1 is linked to rheumatoid arthritis.