The results of a small phase 1 trial of GAD gene therapy in Parkinson's disease published in 2007 suggested the experimental treatment was safe. But to assess its effectiveness, the phase 2 trial was designed such that both the patients and the researchers were unaware who would get the therapy. This meant half the patients would have catheters tunneled into their brains only to receive the injectable equivalent of a sugar pill, a chance Liskiewicz was willing to take.
"It was just the promise of a better life," he said. "I just had faith in it, I guess."
Two months after the surgery, Liskiewicz knew he had received the treatment.
"I don't know why, I just did," Liskiewicz said. "I noticed small improvements. I could tell they weren't coincidental."
His wife, Constance Smith, noticed them too.
"Most of the time Walter looked angry or frustrated," Smith said, describing the Parkinsonian mask that prevents patients from expressing their emotions. "I missed the smile, the warmth that his expressions conveyed. After the surgery I noticed that he could smile."
Liskiewicz said he's "light years better" than a year ago before the trial. He still takes drugs but at half the previous dose, and says they work even better. Now he spends less than 5 percent of his time in his chair.
"I'm mobile. It's a great feeling."
According to the results of the trial, patients who received gene therapy had a 23.1 percent improvement in their motor score in six months of follow-up compared with a 12.7 percent improvement in patients who received a sham surgery and placebo; a difference that was statistically significant.
"This is not a cure," his wife said. "But it has dialed his disease back 10 years."
But some experts argue that deep-brain stimulation is still more effective.
"The extent of improvement arguably appears to be less than that documented for DBS [deep-brain stimulation]," said Dr. William Weiner, chief of neurology and director of the University of Maryland's Parkinson's Disease and Movement Disorders Center, adding that "new does not mean better."
Weiner said future studies should put gene therapy head-to-head with deep-brain stimulation rather than compare it to placebo.
Dr. Michael Okun, medical director of the National Parkinson Foundation, agreed, adding that a longer followup is needed to assess delayed benefits risks.
"This is an important study particularly in terms of safety," Okun said. "It opens the door to the hope for better symptomatic therapies in [Parkinson's disease], though patients should clearly understand their limitations, and that these are not neuroprotective therapies."
Liskiewicz is glad to have more functional time to work on his music and enjoy life with he wife and their two children. He hopes the trial offers new hope to people with Parkinson's disease.
"I hope it shows them that they're working on things that can actually work," he said. "They're in the pipeline.
"There's going to be a lot of things coming out in the near future that can improve their quality of life and well being."