Of note, FGF21 levels measured in the acute phase were previously associated with cognitive and multidomain deficit PRO clusters relative to MIN in this cohort (18), and FGF21 has been proposed as a biomarker for chronic inflammation in ME/CFS (77), a complex chronic disease that overlaps clinically with LC. This evidence concerns the gene FGF21 and myalgic encephalomeyelitis/chronic fatigue syndrome.