Slevin JT, Gerhardt GA, Smith CD, Gash DM, Kryscio R, Young B: Improvement of bilateral motor functions in patients with Parkinson disease through the unilateral intraputaminal infusion of glial cell line-derived neurotrophic factor. Journal of neurosurgery 102:216-222, 2005. This evidence concerns the gene GDNF and Parkinson disease.