These studies analysed the methylation status of several genes related to immune response (NFATC2IP & FKBP5) (36, 38), mitochondrial function (CPT1A) (37) diabetes and ageing (TXNIP & CAV1) (39, 40), circadian rhythm (CLOCK, CRY2 & PER2) (41) as well as obesity related genes (e.g. FTO) (42). The gene discussed is PER2; the disease is obesity due to melanocortin 4 receptor deficiency.