The potential role of TGF-β1, as a substantial component of cytokine signature, in the occurrence of fatigue, is suggested by a study of Montoya et al. which demonstrated increased serum concentrations of TGF-β1 in patients with chronic fatigue syndrome when compared with those concentrations in healthy controls [59]. Here, TGFB1 is linked to myalgic encephalomeyelitis/chronic fatigue syndrome.