PSEN1 and Alzheimer disease: Current work on biomarkers for AD focuses on various types of Tau, Amyloid, plasma neurofilament light protein (NfL) (Rafii 2018), and genetic markers including the ε4 allele of the apolipoprotein E (APOE) gene, presenilin 1 and 2 (PSEN1, PSEN2) and many more (at least 20 loci were named by Giri et al. 2016, in late-onset AD and this number continues to rise).