Tau RT-QuIC assays were used to quantitate 3R/4R tau seeds in mid-frontal lobe brain tissue (Fig. 1) from 67 cases including subjects with neuropathologically confirmed AD (n = 16), Lewy body disease (LBD: Parkinson’s disease (PD) n = 8, dementia with Lewy bodies (DLB) n = 13), multiple system atrophy (MSA) (n = 6), progressive supranuclear palsy (PSP) (n = 6), corticobasal degeneration (CBD) (n = 6), and controls inclusive of two Braak 0 cases with Huntington’s disease, and 10 cases with no or mild Alzheimer’s changes (Braak 0–II) (n = 12) (Supplementary Table 1, online resource). This evidence concerns the gene MAPT and juvenile Huntington disease.