GDNF gene therapy phase I clinical trial
Unfortunately I don't expect much from this clinical trial:
However, it could be used in combination with a med unfolding misfolded alpha-synuclein in order to regenerate new neurons.

I also wonder what would happen if a person without a neurologic disease gets treated with this. Could this make the person much smarter ? It makes me think back to the movie "planet of the apes" where monkeys get treated with an experimental PD med and as a consequence of that they get very smart and take control of the world.
The Swedish group that didn't find GDNF restorative used overexpression of alpha synuclein in mice as their PD model. That may not accurately reflect the actual disease where the build up of alpha syn may be more gradual in the cell and will probably not happen in a large volume of cells simultaneously............
Bartobob, a far as my knowledge reaches certain people with PD have a gene that causes overexpression of alpha-synuclein. These people will eventually get PD. And the cause of this PD is clumping of alpha-synuclein. This clumping is killing the neurons and disturbing the mechanism that makes neurotrophic factors grow and protect neurons; as well as causing an auto-immune response that also fastens PD. This clumping is present in all PD and probably the number 1 cause leading to PD.

So yes, you are true that majority of people with PD do not have overexpression of alpha-synuclein. However, the clumping of alpha-synucline is present in all forms of PD. And in this environment of clumped alpha-synuclein neurotrophic factors don't seem to work according to several research papers I already read. Neurotrophic factors do work well when PD is induced by toxins. But till now all research I read with neurotrophic factors on models with clumped alpha-synuclein seem to conclude that neurotrophic factors simply don't work.

I read on neurotalk that many people waited to participate in PD research in order to be able to participate in this one. They have high hopes that this is THE CURE. However, I tend to think this is no cure either. I hope for those people I am wrong. But based on current research this is the only conclusion I can make. However, it might be helpful if combined with Affiris vaccin or with LMTX. Future will tell.
I see a brighter future of neurotrophic factors for people that got a stroke.