Future Promise
- Retinal pigment epithelial cells
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 a double-blind trial is underway.
By the year 2006, gene therapy has been tried in a few PD patients. However it 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 . Studies are still in progress.
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.
