TGFB1 and myalgic encephalomeyelitis/chronic fatigue syndrome: When divided according to fatigue severity (Chalder Fatigue Questionnaire), CFS patients with the highest fatigue score (≥ 20) displayed the strongest associations between TGF-β and neuroendocrine markers, whereas CFS patients with the lowest fatigue score (< 20) had a pattern of associations that was more similar to the one observed in healthy controls.