Despite increases in 18F-DOPA uptake on positron emission tomography (PET) imaging reported in many clinical trials with GDNF, no significant improvement in motor function has been observed in the participants in placebo-controlled trials, possibly in part due to the inability of GDNF to improve the health of morbid DA neurons in PD patients [5]. The gene discussed is GDNF; the disease is Parkinson disease.