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An experimental treatment that stimulates the spinal cord may help people with a paralyzing genetic disorder. NPR's Jon Hamilton reports on a study of three people with a rare inherited condition.
JON HAMILTON, BYLINE: Doug McCullough was 11 when he was diagnosed with spinal muscular atrophy, or SMA, a disorder that kills off motor neurons in the spinal cord. McCullough is in his 50s now and relies on two canes or a wheelchair to get around.
DOUG MCCULLOUGH: As a person with a progressive disease, you never get any better. You're either maintaining or you're getting worse.
HAMILTON: So McCullough had low expectations when he signed up for a four-week experiment at the University of Pittsburgh School of Medicine. Scientists there temporarily implanted wires in his spine. Then in the lab, they began delivering pulses of electricity to certain nerves.
MCCULLOUGH: That first afternoon, they were like, do you feel anything? You're like, no. And then they'd start turning it up a little bit, and then you'd start feeling this faint pulse inside your body.
HAMILTON: Specifically in his legs. And over the course of the experiment, McCullough's legs regained some function. He could walk farther. His gait was better. His legs felt stronger, even when the spinal stimulator wasn't connected.
MCCULLOUGH: And after some days, my legs just felt supercharged, just like, man, I feel like I can walk a mile.
HAMILTON: Two other volunteers with SMA also improved. The youngest was 20, says Marco Capogrosso, one of the scientists in charge of the experiment.
MARCO CAPOGROSSO: He improved so much that he could walk from the family housing where they were staying for the trial to our lab, and he couldn't do that before.
HAMILTON: There are now drugs that can slow or stop the loss of motor neurons in people with SMA. But the treatment doesn't restore the muscle function they've lost. Capogrosso's team had been using spinal stimulation to boost arm strength in stroke patients and thought the approach might work on the leg muscles in people with SMA. In both cases, the idea was to get more out of the relatively small number of nerve cells that remain intact. Capogrosso says the results with SMA patients were remarkable.
CAPOGROSSO: Friday, they would come in the lab, do their tests, and then they would go home. Then on Monday, they would be back. We would reassess their strength 'cause they were doing it on a daily basis. And suddenly, they had 20% more strength for the knee extension.
HAMILTON: Much of the improvement was maintained even when the stimulator wasn't turned on. Capogrosso thinks that's because stimulation had helped reestablish communication between the remaining motor neurons and other neurons involved in the circuit that allows walking.
CAPOGROSSO: They had much less motor neurons left because some of those died. But now they were starting working as normal motor neurons. So this increasing strength that we observed was because their cells were better able at controlling their muscle.
HAMILTON: The result, which appears in the journal Nature Medicine, supports an idea proposed in 2011 by George Mentis at Columbia University.
GEORGE MENTIS: What people thought until that time is that this is really a motor neuron disease, and if you fix the motor neurons, you will be fixing the disease.
HAMILTON: But Mentis showed that in mice with SMA, the disease also disrupts connections between motor neurons, which tell a muscle when to contract, and sensory neurons, which monitor what that muscle is doing. Mentis says the results in Pittsburgh suggest that spinal stimulation improves these connections and could make a big difference to people with SMA.
MENTIS: During that month of electrical stimulation, we never reached a plateau. They were still improving. So obviously, you will say to me, oh, my God, can they improve anymore? The preliminary data says yes.
HAMILTON: Mentis says spinal stimulation also might help people with other diseases that affect movement, including ALS and Parkinson's.
Jon Hamilton, NPR News.
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