Taken together, these limited number of available studies show that although TauC3 is expected in the most common sporadic tauopathies, caspase-6 activation, and caspase-6 cleaved tau fragments are several levels of magnitude more predominant in 3R/4R and 3R tauopathies than in 4R tauopathies, making biomarkers based on caspase-6 cleaved tau potential tools to discriminate between AD and 4R-tauopathies. The gene discussed is CASP6; the disease is Alzheimer disease.