Tau phosphorylation is a well-described post-translational modification in tauopathies, including Alzheimer's disease, and plays a critical role in mediating tau neurotoxicity in Drosophila[27], [28], [29], but there was no change in tau phosphoepitope levels to explain the modulatory effect of cathepsin D (Figure 2). The gene discussed is CTSD; the disease is early-onset autosomal dominant Alzheimer disease.