MMP9 and myalgic encephalomeyelitis/chronic fatigue syndrome: While often misdiagnosed as ME/CFS due to symptom overlap, CIRS is distinguishable by a panel of consistently altered markers, including elevated transforming growth factor beta 1 (TGF-β1), matrix metalloproteinase 9 (MMP-9), complement component 4a (C4a), and reduced melanocyte stimulation hormone, (MSH), as well as abnormalities in adrenocorticotropic hormone (ACTH)/cortisol, antidiuretic hormone (ADH)/osmolality, vascular endothelial growth factor (VEGF) and visual contrast sensitivity (VCS) [2].