The examples include the enrichment of phosphorylated tau (p-tau) at Thr-181 relative to total tau in brain-derived EVs in the blood in the early stages of AD [97-99], elevated levels of cathepsin D, and Lamp-1 proteins in neuron-derived EVs in the blood, ~10 years before the diagnosis of AD [100-101], and increased concentration of alpha-synuclein and neurofilament light chain in patients with Parkinson’s disease (PD) [102-104]. The gene discussed is CTSD; the disease is Alzheimer disease.