New data suggest that the LC is one of the earliest sites of tau pathology in AD and the initiator in the transmission of NFT during the progression of AD; however, its elongated shape and ultra-small dimensions, ~6–22 mm3 (Theofilas et al., 2017), pose a significant challenge for PET even with state-of-the-art scanners. This evidence concerns the gene MAPT and Alzheimer disease.