Genome-wide methylation analysis of a large population sample shows neurological pathways involvement in chronic widespread musculoskeletal pain

Chronic widespread musculoskeletal pain (CWP), has a considerable heritable component, which remains to be explained. Epigenetic factors may contribute to and account for some of the heritability estimate. We analysed epigenome-wide methylation using MeDIPseq in whole blood DNA from 1708 monozygotic (MZ) and dizygotic (DZ) Caucasian twins having CWP prevalence of 19.9%. Longitudinally stable methylation bins (lsBINs), were established by testing repeated measurements conducted ≥3 years apart, n=292. DNA methylation variation at lsBINs was tested for association with CWP in a discovery set of 50 MZ twin pairs discordant for CWP, and in an independent dataset (n=1608 twins), and the results from the two samples were combined using Fisher's method. Functional interpretation of the most associated signals was based on functional genomic annotations, gene ontology and pathway analyses.Of 723,029 signals identified as lsBINs, 26,399 lsBINs demonstrated the same direction of association in both discovery and replication datasets at nominal significance (P ≤ 0.05). In the combined analysis across 1708 individuals, while no lsBINs showed genome-wide significance (p<10-8), 24 signals reached p≤9E-5, and these included association signals mapping in or near to IL17A, ADIPOR2 and TNFRSF13B. Bioinformatics analyses of the associated methylation bins showed enrichment for neurological pathways in CWP. We estimate that the variance explained by epigenetic factors in CWP is 6%. This, the largest study to date of DNA methylation in CWP, points towards epigenetic modification of neurological pathways in CWP and provides proof of principle of this method in teasing apart the complex risk factors for CWP.