GDNF and progressive supranuclear palsy: Searching clinicaltrials.gov yielded two additional studies that were not published: a phase 1 study on continuously infused intracerebral (IC) recombinant-methionyl human GDNF (r-metHuGDNF) for the treatment of idiopathic Parkinson’s disease (NCT00006488) and continuously infused r-metHuGDNF to treat progressive supranuclear palsy (NCT00005903).