Initial results from the first human clinical trial of gene therapy treatment for Parkinson’s disease suggest the approach can significantly reduce symptoms of the disease.
After a year, the 12 patients in the trial showed an average 25% improvement in motor control. The researchers say the new treatment shows no signs of reducing immunity – gene therapy for other illnesses has caused fatal immune-system complications.
There is currently no cure for Parkinson’s disease, a fatal degenerative brain condition that causes tremors, speech difficulties and progressive loss of mobility, among many other symptoms.
Sufferers can take medications such as levodopa, which helps by elevating levels of the chemical messenger dopamine in the brain. But people respond less to the drug over time and can experience side effects such as jerky movements.
Researchers hoping to develop a cure for Parkinson’s have now turned to gene therapy. They developed the treatment by engineering a harmless virus to carry genes that encode a protein called glutamic acid decarboxylase, or GAD.
The protein helps make a key nerve signalling chemical called GABA (gamma aminobutyric acid), which inhibits a brain region known as the subthalamic nucleus. This is important because the subthalamic nucleus is typically overactive in Parkinson’s disease due to a loss of dopamine-producing cells elsewhere in the brain.
Matthew During of the Cornell Weill Medical College in New York, US, recruited 12 patients who had been diagnosed with Parkinson’s disease for at least five years and had stopped responding to available treatments. (New Scientist reported the start of the Parkinson’s trial in 2002).
Using a thin, hollow glass fibre, researchers infused a tiny drop of solution containing the engineered virus particles into a tiny area within the subjects’ subthalamic nuclei.
At three-month intervals participants took a test called the unified Parkinson disease rating scale, which assessed their motor control. On average, the patients showed a 25% improvement in their scores on this test by the end of the one year trial. Nine of the patients showed an average improvement of 37%, and one had a 65% improvement.
“As a clinician, I see this as an incredibly promising result,” says Parkinson’s expert Thomas Freeman of the University of South Florida in Tampa, US.
During, who co-founded the company Neurologix to support this approach, says that treating a greater proportion of the subthalamic nucleus with the engineered virus could perhaps lead to even greater improvements.
Another observed benefit of the treatment related to the abnormal cell metabolism that Parkinson’s patients typically show in various brain regions. Brain scans revealed that the gene therapy apparently normalised energy metabolism.
Nonetheless, Freeman says there is a need for long-term monitoring of the trial patients to ensure that no immune system or other side effects occur.
The research was presented at the Society for Neuroscience Meeting in Atlanta, Georgia, US, on Tuesday.