NRGN and depressive disorder: In recent years, Nrgn has been implicated in a variety of neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease, psychiatric disorders such as schizophrenia and depression, and infectious diseases such as Creutzfeldt-Jakob disease, neuro-HIV, and neurosyphilis, and has been reported as a potential biomarker candidate for these conditions [16–20].