THU0001 Differential methylation as a predictor of methotrexate response in patients with rheumatoid arthritis
Authors: N. Nair, D. Plant, S.M. Verstappen, J.D. Isaacs, A.W. Morgan, K.L. Hyrich, A. Barton, A.G. Wilson
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> Methotrexate (MTX) is recommended as the first-line disease modifying anti-rheumatic drug (csDMARD) for the treatment of rheumatoid arthritis (RA), but up to 40% patients do not respond adequately, or experience adverse effects<sup>1</sup>; therefore, identifying blood-based biomarkers that predict treatment response is a research priority. DNA methylation is an epigenetic marker that modifies but does not alter DNA sequence; MTX may act, at least in part, by inhibiting intracellular methyl donor transfer leading to DNA hypomethylation<sup>2</sup> so DNA methylation may act as a biomarker of MTX response. <h3>Objectives</h3> To identify differential DNA methylation signatures in whole blood associated with response to MTX in patients with RA. <h3>Methods</h3> DNA methylation was measured using the HumanMethylation450 BeadChip in DNA samples from individuals recruited to the Rheumatoid Arthritis Medication Study (RAMS). Demographic and clinical data were collected prior to starting MTX (baseline) and at 6 months after commencing MTX. DNA was extracted from whole blood samples collected at baseline and at 4 weeks from patients who, at 6 months, had a EULAR good response (n=36) or EULAR poor response (n=36) to MTX. Differentially methylated positions (DMPs) between baseline and 4 weeks, and between good and poor response groups were identified using a linear model, adjusting for gender, age, cell composition, baseline disease activity score (DAS28), and smoking status. Additional analyses were performed to assess the association between methylation and change in DAS28 score and the individual DAS28 components over 6 months. DMPs with significant differences were selected for replication by pyrosequencing in an independent group of 100 patients with both baseline and 4 week samples available for testing. Using genome-wide genotype data for the same patients, replicated DMPs were investigated for methylation QTLs (meQTLs). <h3>Results</h3> The initial analysis identified differential methylation between good and poor responders at 2 CpG sites (DMPs) in samples taken at 4 weeks, with response status determined at 6 months (p-value&lt;10–5). Three other DMPs were associated with change in tender joint count, another 3 DMPs with change in swollen joint count, and a further 4 DMPs were associated with change in C-reactive protein (CRP). Of the 12 DMPs, 4 showed replicated association with improvement of swollen joint count and lower CRP levels at 6 months in the pyrosequencing dataset (p-value&lt;0.01). However, there were no meQTLs identified at these loci. <h3>Conclusions</h3> These results suggest DNA methylation may provide a biomarker of MTX response but requires replication in other larger data sets. <h3>References</h3> [1] Verstappen SMM, et al. Int. J. Clin. Rheu2012;7(5):559–567. [2] Kim Y, et al. J. Lab. Clin. Med1996;128:165–172. <h3>Disclosure of Interest</h3> None declared