Crossroads in GDNF therapy for Parkinson's disease.

The development of a neuroprotective or neuroregenerative therapy for Parkinson's disease (PD) would be a major therapeutic advance. Unfortunately, results from a recent controlled clinical study delivering the neurotrophic factor, glial-derived neurotrophic factor (GDNF), directly into brain did not demonstrate efficacy and safety of such a treatment. A critical review of available data suggests that there are questions that need to be answered before the future of GDNF as a therapy for PD can be determined.