In conclusion, we propose that a combination of clinical evaluation of endothelial function by FMD and/or EndoPAT, along with the detection of circulating Sirt1/eNOS-related miRs, might allow a more sensitive characterization of ED in a subset of ME/CFS patients for better stratification, which will certainly translate into improved treatment possibilities. Here, NOS3 is linked to myalgic encephalomeyelitis/chronic fatigue syndrome.