MAPT and Alzheimer disease: In Alzheimer’s disease, higher QSM, especially in the hippocampus, is seen in amyloid-positive patients.18 Iron may bind to amyloid beta, worsening its toxicity either directly42 or via increased phosphorylation of tau.43 Additional precedents for higher QSM signal in hippocampal regions are those in a beta amyloid transgenic mouse model44 and in a mouse model of tauopathy.45 Future work with post-mortem tissue can clarify the precise pathological proteins driving the magnetic susceptibility changes we found in relation to PD cognition.