The initial studies of human gene therapy for Parkinson's disease has given the green signal to technique showing it to safe, and useful in reducing symptoms for patients, according to the reports of two groups of researchers.
In the neuroscience meetings held yesterday and last week the researchers reported that each of the 24 patients who received therapy in the two separate trials received some benefit and none had significant side effects.
Katie Hood, deputy chief executive officer of the Michael J. Fox Foundation for Parkinson's Research said that gene therapy had a tarnished reputation because of problems encountered in trials against other diseases.
In 1999 the Food and Drug Administration temporarily halted gene therapy trials after an 18-year-old who was treated for a mild genetic disorder died after a violent reaction to the procedure. in 2005 trials were again brought to a standstill after three French children who was treated for inherited immuno- deficiency disease developed leukemia and one of them died.
Hood said, ``It's very encouraging that two companies were able to show benefits with no significant adverse effects. Safety is obviously the first hurdle."
Patients have been cautioned however against placing too much hope in the findings because Parkinson's studies have been infamous for showing placebo effects. Researchers say that only when the techniques are tested in controlled trials, which are now in the planning stages, can they determine whether the benefits are real, and long-lasting or not.
Each year around 100,000 Americans are affected by Parkinson's each year, and is characterized by severe tremors and rigidity in the limbs with loss of muscle control. Its cause although unknown yet has been presumed to be the result of the death of brain cells that produces a neurotransmitter called dopamine. Dopamine plays a key role in transmitting commands from the brain's muscle-control centers.
Same technology was used by both teams for performing gene therapy, wherein a desired gene is inserted into a common virus called adeno-associated virus, which is known to readily infect humans. This virus has never been shown to cause disease. The genes used by both teams were quite different.
The team, led by Dr. Matthew J During from the Weill Cornell Medical Center in New York, used a gene responsible for the synthesis of enzyme, glutamic acid decarboxylase. This enzyme in turn converts compounds in the cell into the neurotransmitter, GABA that controls muscle movements.
Parkinson's disease has been known to be deficient in GABA in the subthalamic nucleus part of the brain.
Although injecting GABA directly into the brain eases symptoms of the disease, the hormone is quickly cleared, which is therefore a limits its benefits. During's team injected one side of the brain of 12 patients with one of three different concentrations of the gene therapy agent.
All 12 patients were found to have an improvement of at least 25 percent on a conventional scoring system that assesses the severity of Parkinson's symptoms, nine of them showed an improvement of at least 37 percent, while five of them were seen to have an improvement between 40 percent and 65 percent. Moreover the patients have observed these benefits to persist for a year unlike the benefits from a placebo effect which are mostly transient.
During said that sophisticated imaging of the patients' brains showed an increase in metabolism on the side where gene therapy was performed, and the amount of increase correlated with the degree of improvement in symptoms.
Neurologix Inc. of Fort Lee, N.J., a company created by During and his colleagues to commercialize the technology are the manufacturers of the gene therapy agent. The study was funded by Neurologix.
The second study was led by Dr. William J. Marks Jr. of the University of California at San Francisco, Here the gene for growth factor, neurturin closely related to the better-known growth factor GDNF was used in the study. Injection of GDNF into the putamen section of the brain has been shown to possibly impede, and perhaps even reverse, the loss of dopamine-secreting cells.