All the time I read papers claiming that they found abnormality X or Y or Z, but very rarely are those abnormalities replicated in multiple well designed and reliable studies. It seems like it's always one or several of the following: poorly designed study giving misleading results, novel study that never gets replicated, novel study that gets replicated, but then gets contradicted later. As far as I am aware of, the only physiological abnormality that has been replicated enough to be considered proven is a performance reduction in a 2 day CPET test. So, after so much research the only thing that we can conclusively say, with scientific certainty, is that people with ME have reduced cardiovascular performance after demanding activities. And that's it. Not even PEM is a proven entity, since a CPET test can only detect reductions cardiovascular performance, but not reductions in mental performance and physical symptoms. Pretty disappointing if you ask me. Is anyone aware of other abnormalities in ME/CFS that there is scientific consensus about? I think there was quite a few studies showing abnormal lactate build up, but my memory is a bit fuzzy on those.