We investigated differences in MRI cortical thickness estimates between groups, and in the 21 autopsied LBD patients (LBD−AD = 14, LBD+AD = 7), directly tested the association between antemortem MRI and post‐mortem burdens of tau, Aβ, and alpha‐synuclein using digital histopathology in five representative neocortical regions. The gene discussed is SNCA; the disease is Alzheimer disease.