Here, we applied the recently developed Receptor-Enriched Analysis of functionalConnectivity by Targets (REACT)20 framework to rs-fMRI data acquired in a cohort of multiplesclerosis patients with high and low fatigue to investigate how changes in restingstate functional connectivity (FC) often reported in multiple sclerosis patientswith fatigue relate to the distribution of the dopamine (DAT), noradrenaline (NET)and serotonin (SERT) transporters. The gene discussed is SLC6A4; the disease is multiple sclerosis.