However, the diagnosis of concurrent Ad in HD was not based on pathology by brain biopsy or amyloid PET or tau PET study but rather on symptoms and findings, such as reduced blood flow patterns in the parietal association cortex, temporal association cortex, posterior cingulate gyrus, and precuneus on single-photon emission computed tomography and elevated phosphorylated tau concentrations in CSF. This evidence concerns the gene MAPT and Huntington disease.