anything is possible
neurologix is pretty much parkinson only company in phase2 trial and it's publicly traded.

if phase2 results are successful they will need to sell more stock to raise funds.

i guess you are asking do investors think parkinson's is a good investment? hard to tell, we'll know more n if neurologix does a phase3 trial, how quickly they raise more money. public companies usually sell new shares to large investors, it's quicker, cheaper, faster.

if you are suggesting pd'ers form a company to develop gdnf, i've read of individuals with relatives with rarer diseases that the drug companies wouldn't touch starting companies, rarely successful. money came from grants, shareholders