DNA Methylation Signatures of Functional Somatic Syndromes: Systematic Review

Abstract

Objective Functional somatic syndromes (FSS) are highly prevalent across all levels of healthcare. The fact that they are characterised by medically unexplained symptoms, such as fatigue and pain, raises the important question of their underlying pathophysiology. Psychosocial stress represents a significant factor in the development of FSS and can induce long-term modifications at the epigenetic level. The aim of this review was to systematically review, for the first time, whether individuals with FSS are characterised by specific alterations in DNA methylation. Methods MEDLINE and PsycINFO were searched from the first available date until September 2022. The inclusion criteria were: 1) adults fulfilling research diagnostic criteria for chronic fatigue syndrome, fibromyalgia syndrome, and/or irritable bowel syndrome, 2) healthy control group, and 3) candidate-gene or genome-wide study of DNA methylation. Results Sixteen studies (N = 957) were included. In candidate-gene studies, specific sites within NR3C1 were identified, which were hypomethylated in individuals with chronic fatigue syndrome compared to healthy controls. In genome-wide studies in chronic fatigue syndrome, a hypomethylated site located to LY86 and hypermethylated sites within HLA-DQB1 were found. In genome-wide studies in fibromyalgia syndrome, differential methylation in sites related to HDAC4, TMEM44, KCNQ1, SLC17A9, PRKG1, ALPK3, TFAP2A, and LY6G5C was found. Conclusions Individuals with chronic fatigue syndrome and fibromyalgia syndrome appear to be characterised by altered DNA methylation of genes regulating cellular signalling and immune functioning. In chronic fatigue syndrome, there is preliminary evidence for these to be implicated in key pathophysiological alterations, such as hypocortisolism and low-grade inflammation, and to contribute to the debilitating symptoms these individuals experience. Preregistration PROSPERO identifier: CRD42022364720.