Finally, we guess a combined use of multiple biomarkers (Table 5) is mandatory to precisely stratify NDDs depicting the essential characteristic of neurodegeneration such as neurodegeneration tout court (e.g., NFL), specific AD (p-tau and β-amyloid 40–42 peptides), and synuclein-related neurodegenerations (α-syn), and synaptic dysfunction (e.g., Ng). The gene discussed is NRGN; the disease is Alzheimer disease.