Consistent with three previously published reports (21–23), while the CSF levels of P-Tau, T-Tau, and NFL in all PCA patients were significantly higher than in the ND group, the lowest among all four AD groups was observed in PCA patients who also showed positive 11C PiB retention, suggesting that PCA, based upon Aβ pathology, may not be as aggressive a disease of tau pathology and axonal neurodegeneration as the other AD subtypes. This evidence concerns the gene NEFL and Alzheimer disease.