Comparisons to the reference data also showed that follistatin levels were significantly lower in the CFS/ME group (p < 0.0001) (Fig. 3c), and therefore, both activin A:follistatin (ActA:FST, p < 0.015) and activin B:follistatin (ActB:FST, p < 0.0001) ratios were significantly higher in CFS/ME patients (Fig. 3d, e), with a greater difference seen for the activin B/follistatin ratio. Here, FST is linked to myalgic encephalomeyelitis/chronic fatigue syndrome.