In response to the current lack of clarity about the brain mechanisms underlyingfatigue in multiple sclerosis, here we used a novel multimodal approach toinvestigate changes in the FC measured at rest associated with the DAT, NET and SERTcircuits in multiple sclerosis patients with high fatigue as compared to those withlower levels of fatigue. The gene discussed is SLC6A3; the disease is multiple sclerosis.