The bottleneck in drug discovery for central nervous system diseases is the absence of effective systemic drug delivery technology for delivering therapeutic drugs into the brain. Although some Adeno Associated Virus (AAV) serotypes can cross the blood-brain barrier and deliver virus genome packaged therapeutic DNA (gene) or RNA molecules to brain cells along with other organs, the AAV9 vector gene transfer technology has several hurdles that have emerged in both preclinical studies and clinical trials.