NRGN and Alzheimer disease: We then compared the CSF concentrations of synaptic-related proteins (i.e., Ng and α-Syn) and AD-core biomarkers (i.e., Aβ-42, pTau, tTau, and the Aβ 42/40 ratio) between AD and n-AD; we found, as expected, statistically significant differences in Aβ-42 (p = 0.017), the Aβ 42/40 ratio (p < 0.001), pTau (p < 0.001) and tTau (p < 0.001); the Aβ42 concentration and Aβ 42/40 ratio were lower in the AD group, while the pTau and tTau concentrations were higher (Table S3).