Recent studies suggested that elevated levels of tau in the blood are not specific to AD, which could also be found in other neuron degeneration conditions, such as Parkinson's disease, frontotemporal dementia, or amyotrophic lateral sclerosis (ALS) (Neumann et al., 2006; Boeve et al., 2022; Pan et al., 2022). This evidence concerns the gene MAPT and Alzheimer disease.