SLC6A3 and Alzheimer disease: While imaging modalities such as fluoro-deoxyglucose positron emission tomography (FDG-PET), revealing occipital hypometabolism or the cingulate island sign, and dopamine transporter–single-photon emission computed tomography (DAT-SPECT), showing reduced striatal dopamine transporter uptake, support diagnosis, biomarker interpretation is challenged by frequent copathology with AD, especially Aβ and tau deposition [84,85].