Central to this process is brain-derived neurotrophic factor (BDNF), crucial for synaptogenesis, neuronal differentiation, and survival, hence its potential as a molecular biomarker for neurological disorders with impaired cognitive and motor function such as Alzheimer’s, Parkinson’s, and Huntington’s diseases, and HIV-associated NCI [8–11]. The gene discussed is BDNF; the disease is Parkinson disease.