A gene therapy for Parkinson's disease that has been tested on monkeys is showing promising early results in a small-scale trial on humans. French researchers reported their findings in the new journal Science Translational Medicine last week.
In Parkinson's disease specific nerve cells in the brain degrade causing severe movement problems, including tremors and the inability to initiate movement. Current drugs used to treat the disease temporarily increase the amount of the neurotransmitter dopamine, which is depleted during Parkinson's. This treatment helps control nerve cell activity, and intermittently alleviates Parkinson's symptoms. However, long term these drugs can cause debilitating side effects, called dyskinesias, that include abnormal involuntary movements like as jerkiness, rigidity and tremor.
The gene therapy involved inserting three genes that produce dopamine, into a deactivated virus. The virus was then injected directly into the brains of monkeys with Parkinson's symptoms. The treatment restored the monkeys' levels of dopamine and corrected their movement problems, for 12 months, without any dyskinesias.
This success in monkeys paves the way for future studies in humans, says Stéphane Palfi, who reported the results of the animal study. 'This is the exact situation that we will face in the clinic,' he explained. Palfi's team has already tested two different doses of the three-gene-containing virus in six human patients, in collaboration with colleagues at Oxford BioMedica.
Researchers say the results are encouraging, as measured in control of Parkinson's symptoms and in side effects such as brain inflammation. They are now investigating an intermediate dose that matches that used in the monkeys, with corrections for brain size. Once the researchers find the optimal dose, they plan to move the experimental treatment into Phase II trials, Palfi says. This trial will test the gene therapy treatments safety and effectiveness.