Previous studies of DNA methylation using whole blood or individual purified cell types have identified differentially methylated positions [DMPs] between patients with active and inactive IBD and healthy controls, and for the classification of different IBD sub-types.25–27 Pharmacoepigenomics is the application of epigenetics to understand inter-individual differences in response to therapeutic drugs.28 DNA methylation sites from whole blood have been identified as effective biomarkers predicting treatment response to methotrexate and anti-TNF in patients with rheumatoid arthritis.29–31. The gene discussed is TNF; the disease is irritable bowel syndrome.