I was a lab assistant for a group of neuroscientists that were studying gene therapy techniques for PD back when I was in college (I was majoring in neuroscience - at a liberal arts college, of all places!). The research was very promising, even back then, in 1998-2000.
If you do a search for gene therapy for PD on www.pubmed.com (the online mecca of peer-reviewed articles), you'll find hundreds of articles about the current research. Pretty technical stuff, but really interesting, especially for those of us with nerd-like tendencies!