Fatigue is one of the most common and distressing symptoms, leading to markedly decreased quality of life among a large subset of patients with a variety of disorders. Susceptibility to fatigue may be influenced by genetic factors including single nucleotide polymorphisms (SNPs), especially in the regulatory regions, of relevant genes. To further investigate the association of SNPs with fatigue in various patient populations, a systematic search was conducted on Pubmed, CINAHL, PsycINFO, and Sociological Abstracts Database for fatigue related-terms in combination with polymorphisms or genetic variation-related terms. Fifty papers in total met the inclusion and exclusion criteria for this analysis. These 50 papers were further classified into three subgroups for evaluation: chronic fatigue syndrome (CFS), cancer-related fatigue (CRF) and other disease-related fatigue. SNPs in regulatory pathways of immune and neurotransmitter systems were found to play important roles in the etiologies of CFS, CRF and other disease-related fatigue. Evidence for associations between elevated fatigue and specific polymorphisms in TNFα, IL1b, IL4 and IL6 genes was revealed for all three subgroups of fatigue. We also found CFS shared a series of polymorphisms in HLA, IFN-γ, 5-HT and NR3C1 genes with other disease-related fatigue, however these SNPs (excluding IFN-γ) were not found to be adequately investigated in CRF. Gaps in knowledge related to fatigue etiology and recommendations for future research are further discussed.

This pilot study examined whether a combined aerobic resistance exercise program reduced fatigue and the potential inflammatory and epigenetic mechanisms in patients with head and neck cancer (HNC) receiving intensity-modulated radiotherapy. The exercise group (N = 12) received a 3-month supervised aerobic resistance exercise intervention that was initiated before a 6-week radiotherapy regimen; the control group (N = 14) received standard care. Fatigue was measured using Multidimensional Fatigue Inventory-20; physical function measures included a 6-minute walk distance (6MWD), chair stands, bicep curls, and hand grip strength. Inflammatory markers and DNA methylation data were acquired using standardized protocol. Patients were mostly white (93%) and male (81%) with a mean age of 57 years. At the end of the intervention, the exercise group had a marginal decrease in fatigue compared with the control (−5.0 vs. 4.9; P = 0.10). The exercise group had a significantly greater improvement in 6MWD (29.8 vs. −55.5 m; P = 0.04), and a marginally smaller decline in hand grip (−0.3 vs. −5.8 lbs; P = 0.05) at the end of the intervention than the control. No significant difference in inflammatory markers was observed between groups. Lower plasma interleukin (IL) 6, IL1 receptor antagonist, tumor necrosis factor α (TNFα), soluble TNF receptor II and C-reactive protein were significantly associated with increased 6MWD, chair stand, and bicep curl at the end of the intervention (p < 0.05). Among the 1152 differentially methylated sites (DMS) after intervention (p < 0.001), 163 DMS were located in gene promoter regions. Enrichment analysis suggested that the top 10 upstream regulators were associated with tumor (HNF4A, RPP38, HOXA9, SAHM1, CDK7, NDN, RPS15) and inflammation (IRF7, CRKL, ONECUT1). The top 5 diseases or functions annotations of the 62 hypermethylated DMS indicated anti-tumor and anti-inflammatory effects that might be linked to exercise. These findings suggest that exercise may improve physical performance and reduce fatigue, which could be further linked to decreased inflammation, during active radiotherapy for HNC patients. Larger studies are warranted.