Table 1.

Inclusion and exclusion criteria

Inclusion criteria 1. Any prospective or retrospective study measuring peripheral blood leukocyte DNA methylation in both paediatric or adult IBD patients [cohort, case-control, RCT] 2. Epigenome-wide association studies [EWAS] and targeted DNA methylation study designs 3. DNA methylation analysis performed on peripheral whole blood or specific peripheral blood cell types 4. Studies comparing DNA methylation between Crohn’s disease and ulcerative colitis or comparing either disease with healthy controls Exclusion criteria 1. Studies using intestinal tissue samples 2. Studies investigating DNA methylation markers primarily in patients with cancer or pre-stages of cancer 3. Studies with fewer than five included patients per phenotype 4. Case reports, narrative reviews, in vitro studies [e.g. using cell lines], studies of genetic [rather than epigenetic] mutations or animal studies