MONDAY, Nov. 6 (HealthScout) -- Neuroscientists at Johns Hopkins say they've taken the first steps toward finding a cure for paralyzing disorders like Lou Gehrig's disease and spinal muscular atrophy (SMA).

After injecting stem cells into paralyzed rats and mice, some of the rodents could move their legs again, the researchers say. Stem cells are primitive unspecialized cells from which all types of specific specialized cells are derived.

"I think stem cells represent a new potential strategy against inherited neurological disorders," says lead researcher Dr. Douglas Kerr, an assistant professor of neurology at Hopkins. "It's a very rare person who feels this won't benefit patients ultimately.

"The research on restoring neurological function is in its infancy. We still have a long way to go, but it's certainly a first step," Kerr says. Results of the study will be presented this week to the Society for Neuroscience meeting in New Orleans.

SMA is the most common inherited neurological disorder and the most common inherited cause of infant death from a neurological disease. It affects between 1 in 6,000 and 1 in 20,000 infants.

Lou Gehrig's disease -- amyotrophic lateral sclerosis (ALS) -- affects about 20,000 Americans. With ALS, motor nerves from the brain to the spinal cord, and from the cord to muscles, deteriorate and eventually cause complete paralysis and death.

The Hopkins researchers injected neural stem cells into the spinal fluid of paralyzed mice and rats. The creatures had been paralyzed by an animal virus that attacks motor neurons from the spinal cord to the muscles. Within several weeks, the stem cells had migrated to a region of the spinal cord that contains motor nerve cells.

Half the paralyzed rodents were able to place their hind feet on the ground after the infusion of stem cells, the researchers say.

"The study is significant because it's one of the first examples where stem cells may restore function over a broad region of the central nervous system," Kerr says.

Arthur Burghes, a molecular biologist and SMA expert at Ohio State University, describes the Hopkins study as very exciting.

"Their basic question is very interesting, and that is, can you replace neurons -- can you make functional connections? If we can work that out, it has major significance," Burghes says.

If the research progresses successfully, stem cell therapy to treat motor neuron disease could be ready to test in people in two to four years, Kerr says.

"It's tough to know [just when]," he says. "We think of stem cells as a drug, and like any drug, we must make sure it won't harm someone. These are powerful cells and potentially can turn into anything, [like] cancer. We don't want to disrupt the function that the patient still has."

Stem cell researchers also don't want to make the same mistakes made by gene therapy researchers.

"We're about a decade behind gene therapy, but they may have rushed into human trials too early. The first studies were ineffective, and there was a lot of publicity about doing harm to patients. This shakes public confidence, and we don't want to repeat their mistakes," Kerr says.

Also, he says a critical question needs to be answered before moving on.

"Some [of the paralyzed rodents] got better, but we don't know why they got better," Kerr says. "There are two possibilities: The stem cells went to an area of the spinal cord that was damaged, and they recreated the motor unit, or these cells merely acted as a support to increase the function of the remaining neurons."

The use of stem cells has been controversial because the source of the cells is sometimes human fetuses. However, Kerr says the neuron stem cells used for this research "are now grown in a tissue culture indefinitely so we don't need to keep renewing the supply.

"Some have been growing for eight to 10 years," he says.