I've just realized there was a thread discussing a paper about corticosteroid-binding-globulin deficiency: https://www.s4me.info/threads/revie...s-related-disorders-2014-marathe-torpey.8308/ I (re-)discovered that thread after I decided to post this thread. https://rarediseases.info.nih.gov/diseases/13101/corticosteroid-binding-globulin-deficiency I am not entirely sure which definition for CFS they use, but I think it's "chronic fatigue", including fast fatiguability (also of the muscles); they also describe something that might be PEM. CBG researchers don't view CBG deficiency as psychological, although some have a psychiatric background (because they learnt that "fatigue" is not always depression). It was found and confirmed that I (besides another rare mutation in ITPR3 which is being researched right now) have a known, rare gene variant of SERPINA6 which might explain part of my symptoms. Since CBGD is very rare, only a small portion of pwME might have CBGD (and maybe not solely because it doesn't explain ME symptoms entirely...). I also learnt that neuropathies don't seem to occurr in CBGD, which are not uncommon in ME (and I have them, too). I don't know much about treatment options but they don't seem to be awesome. So the worth of this diagnosis to me is to have one (objective) cause for some of my symptoms.