Patients with Parkinson's disease gradually lose cells in the brain that produce the signaling molecule dopamine. As the disease advances, patients lose the ability to control their movements.
A small group of patients with advanced Parkinson's disease were treated with a retroviral vector to introduce three genes into cells in a small area of the brain. These genes gave cells that don't normally make dopamine the ability to do so. After treatment, all of the patients in the trial had improved muscle control.