For PD, (α-syn + ASC)/Aβ seems most promising (in cohort 1: AUC = 97% and 3.1-fold increase, in cohort 2: AUC = 93% and 4.9-fold increase) and for early AD the serum (p-tau-AT8 + ASC)/Aβ ratio gives excellent discrimination (AUC = 92%) and a dynamic range of 6.2. This evidence concerns the gene MAPT and Alzheimer disease.