Gene therapy is an experimental method of treating Parkinson's using DNA rather than drug-based treatment. Gene therapy involves introducing a piece of DNA into a cell (using carefully engineered viruses) which will cause the cell to produce proteins that it usually does not (either by nature or as a result of a genetic mutation). There have recently had a number of announcements regarding gene therapy for Parkinson's, which are worth discussing here.

Firstly, at the 2018 Annual Meeting of the American Neurological Association (ANA), Voyager Therapeutics provided an update on their gene therapy approach for Parkinson's. This treatment is called VY-AADC01. It is a genetically engineered virus - in which all of the disease-causing components have been removed, resulting in a very effective biological delivery system - that is then injected into the brain. The virus is delivered to a region called the putamen. The putamen is where the chemical dopamine is normally active, but in people with Parkinson's there is a severe reduction in the amount of dopamine being produced.

VY-AADC01 is a gene therapy approach which helps with the production of dopamine. By infecting cells in this part of the brain with VY-AADC01, researchers are hoping to stimulate the production of dopamine in the region of the brain where it is most needed in people with Parkinson's.  The update provided by Voyager Therapeutics was that this therapy - currently being tested in a Phase Ib clinical trial - was well tolerated, and the beneficial effects of the treatment were maintained for at least 36 months (the length of the follow up thus far). These beneficial effects include a clinically meaningful 3.5-hour improvement in "ON" time (as determined by the patient) and many of the participants have been able to reduce their Levodopa treatment.

This is an impressive result considering that this trial is being conducted in 15 people with Parkinson's who experience motor fluctuations despite optimal treatment.

The second piece of news from the world of gene therapy for Parkinson's is that the biotech company Axovant Sciences has started their clinical trial of AXO-Lenti-PD. Like the Voyager therapeutics approach, the Axovant treatment is also attempting to increase levels of dopamine in the putamen region of the brain, but the AXO-Lenti-PD virus contains more components of dopamine production than the VY-AADC01. This will hopefully reduce the need for Levodopa therapy. AXO-Lenti-PD is a new version of a previous gene therapy treatment called Prosavin which was clinically tested several years ago. The new Axovant trial will be conducted in the UK and France, assessing up to 30 people with Parkinson's, and will be divided into 2 parts: Part A involves testing 3 different doses of AXO-Lenti-PD and Part B participants will receive the optimal dose determined in Part A (or sham/placebo surgical procedure) and be followed over time.