Gene therapy show tremendous promise when it comes to fighting the battle of 
Parkinson’s. Parkinson’s disease is associated with degeneration or death of dopamine producing nerve cells in the basal ganglia. As these cells die, movement problems become worse. See Parkinson’s overview to learn more…
What is gene therapy? Gene therapy involves inserting a specific gene into a cell so the recipient cell can use that gene to produce the gene product, something otherwise missing in this cell.
This therapy is especially important to conditions like Parkinson’s disease since dopamine nerve cell lost is a known problem in this condition. Gene therapy can alter the course of Parkinson’s diseases if the gene can be turned on or ‘expressed’ in brain cells to produce more dopamine or promote healthier cells less likely to die.
How is gene therapy performed? Once a potentially helpful gene is identified, scientists need to find ways to incorporate that gene into a nerve cell. One technique is to use viruses that do not cause human disease but do get into or ‘infect’ cells. Once such virus is the adenovirus. The desired gene is incorporated into the DNA of the adenovirus. This virus is surgically placed into the target area of the brain where it gains entry to the nerve cell is loans its DNA to that cell.
Are gene therapies available for Parkinson’s disease? Gene therapy is in the research phase although results are promising. The following studies showed initial promise with improvement in Parkinson’s movement symptoms in open label studies tested on a small number of patients. Two promising gene therapy studies are highlighted below:
- Nerve Growth Factor
- Cere-120. This gene produces neurturin a growth factor similar to GDNF designed to promote cell sprouting and cell health. The hope is that this action will reduce the number of dopamine nerve cells that degenerate or die over time. A phase 2 research trial with a sham surgery arm (patients that received the Ceregene 120 product were compared to patients that underwent surgery without the treatment to control for the placebo effect) did not show a statistically significant difference in movement symptoms after one year. However , a closer look at the results did show some benefit if the patient had milder disease and when patients were followed over 2 years rather than one year.
- Another study is underway using different doses and brain placement, and a longer follow-up period.
- Genes that Change Enzymes
- Glutamic acid decarboxylase (GAD). This enzyme increases the breakdown of glutamate to a chemical called GABA. Glutamate is present in excess in the subthalamic nucleus (STN). Reducing this neurotransmitter appears to cause similar effects as STN DBS surgery. A sham controlled study in moderately advanced PD showed a some improvement in motor control in the gene therapy group compared with placebo. Effects were not as large as current treatment with DBS and effect was measured after 6 months so longer term results will be needed.
- Unanswered Questions
- More work will need to be done before gene therapy is proven safe and effective. To date, positive results have not been associated with dramatic motor improvement and the effects over a longer period of time will be needed.
- Additional concerns are whether this therapy can lead to unanticipated gene mutations and immune responses that would not be reversible.
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Author: Monique Giroux, MD
Copyright 2011 Northwest Parkinson's Foundation Wellness Center