Experimental Therapies
Cell Transplant Therapy
Transplant of fetal substantia nigra cells has been performed in several hundred patients to date in multiple centers throughout the world. While results have been encouraging in some individual patients, two recent double-blind placebo-controlled studies showed that consistent benefit was only seen in young PD patients (age 60 or below), and side effects in some patients were significant. In particular, some patients developed off-medication dyskinesias (uncontrolled movements) even without any levodopa or other dopaminergic medication. The lack of consistently good results and the significant side effects encountered have been interpreted by the scientific and medical community to indicate that further research in animal models of PD is needed to improve upon what has been observed to date before more studies in PD patients are undertaken.
Another cell transplant technique that shows some promise is the use of retinal pigment epithelial cells. These cells are derived from tissue at the back of the eye, and they produce and release dopamine. An open-label trial in six advanced PD patients has shown promise, and as of mid-2004, a double-blind trial is underway.
Gene Therapy
As of 2004, gene therapy has been tried in only a few PD patients, and is still highly experimental. While experiments in animal models of PD have shown promise, further research is needed. The only publicized trial is of delivery of the gene for glutamic acid decarboxylase (GAD) to the subthalamic nucleus or STN. GAD is a key enzyme in the production of the inhibitory neurotransmitter GABA. Gene therapy with GAD is meant to increase GABA production, reducing STN activity in the manner of STN DBS. Monitoring is still in progress.
Growth Factor Delivery
Glial cell-derived neurotrophic factor (GDNF) stimulates sprouting of dopamine neurons in animal models. Direct delivery of GDNF to the brain has produced promising results in an open-label trial in a small number of patients, but by mid-2004 a larger, double-blind trial failed to show efficacy. Further research is needed, especially regarding how to improve delivery of growth factors to the correct targets in the brain.
