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Transport Problems Cause Motor Neuron Degeneration

For release: Thursday, May 1, 2003

A new study shows for the first time in humans that nerve cell transport problems could play a key role in the degeneration of motor neurons, the nerve cells that control movement. The finding is an important step toward understanding the biology of motor neuron diseases and could lead to the development of effective treatments.

Researchers studied 19 members of a family afflicted by a rare, gradually progressive neurological disease that causes difficulty breathing and speaking, and weakness in the face, arms, hands, and feet.

“People with these symptoms really suffer, so we’re very motivated to find its cause and figure out what to do about it,” says study author Kenneth Fischbeck, M.D., senior investigator in the Neurogenetics Branch at the National Institute of Neurological Disorders and Stroke (NINDS). “This study also gives us clues about other diseases involving motor neuron degeneration.” The study appeared in the April 2003 issue of Nature Genetics 1 .

Dr. Fischbeck and colleagues at the NINDS found a mutation in the gene for a protein called dynactin, which is responsible for carrying signals from muscles to nerve cell control centers and eventually to the brain. Dynactin is part of a complex of proteins that serves as a transport system essential for the proper functioning of motor neurons.

Earlier studies found that mutations in two other proteins in the same complex cause motor neuron degeneration in mice. Researchers have also uncovered some evidence implicating nerve cell transport problems in amyotrophic lateral sclerosis (ALS), or Lou Gehrig’s disease, which is similar to the disease studied in this study but also affects upper motor neurons.

“The idea that cell transport plays a role in motor neuron degeneration has been out there for a long time,” says Dr. Fischbeck. “That’s why we’re excited about this study - it proves for the first time in humans that disrupting nerve cell transport leads to motor neuron degeneration.”

The study will help researchers understand the biology of motor neuron diseases in humans. It also makes it possible to accurately diagnose the motor neuron disease in this family.

Dr. Fischbeck says studies need to be done to develop strategies for circumventing the transport defect. Researchers need to find which key cellular factors help nerve cells survive, he says, so that enhancing those factors or finding another way to transport them might help compensate for the mutation in dynactin causing degeneration.

Dr. Fischbeck likens dynactin and the other subunits in the protein complex to cars on a freight train carrying important cargo from one point to another. “We need to find out what the cargo is. What information is in those freight cars, and can we find a way to deliver it by some other means?” he asks.

Once researchers can pinpoint the nerve signals and growth factors transported by this protein complex, they can start to develop effective treatments for motor neuron diseases, Dr. Fischbeck adds.

1 Puls I, Jonnakuty C, Holzbauer ELF, Tokito M, Mann E, Floeter M, Bidus K, Drayna D, Oh SJ, Brown RH, Ludlow CS, Fischbeck KH. “Mutant dynactin in motor neuron disease.” Nature Genetics , March 9, 2003.

- By Tania Zeigler


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Last Modified March 31, 2016