> This study shows that endoplamic reticulum (ER) stress–induced WASF3 protein localizes to mitochondria and disrupts respiratory supercomplex assembly, leading to decreased oxygen consumption and exercise endurance. Alleviating ER stress decreases WASF3 and restores mitochondrial function, indicating that WASF3 can impair skeletal muscle bioenergetics and may be targetable for treating fatigue symptoms.

So it's a stress response, not necessarily causal. It's long been suspected that some sort of perennial stress state was involved in this problem (anything from adrenal fatigue to illness genes never turning off). So does this tell us more or is this just another biomarker?

Though I say 'just', finding a biomarker for CFS would still be something people could be tested for, which is way better than where we are now.