Research Update
Something in the way they move clue to Huntington's
CMAJ 2000;162:1196
American researchers believe they have identified both the mechanism that is associated with movement problems in Huntington's disease (HD) and the part of the brain that causes them. They have also discovered that subtle jerkiness in movements may appear in patients with HD long before other clinical symptoms are evident (Nature 2000;403:495-6).
"This study identifies a change in motor coordination long before we can see it on clinical examination," says Dr. Christopher Ross, professor of psychiatry and neuroscience at Johns Hopkins University. "This can be very useful. We are now trying to develop treatments for Huntington's disease. The problem is, how do you study a drug in the absence of any markers for the disease? This, we hope, will serve as a marker."
 | Brain section from a patient with Huntington's disease. [Photo courtesy of Kevin Roth and Robert Schmidt, Washington University, St. Louis, Mo.] |
The researchers found that HD involves a dysfunction in the way the brain monitors movement, specifically in the way it corrects small errors in movement. Researchers examined 11 asymptomatic patients who were known carriers of the HD gene, 16 others with symptomatic HD, and 3 subjects who did not have the HD gene but whose parents have the disease, as well as 12 healthy controls. (A second, similar study included 6 control subjects with cerebellar injuries.) Researchers asked the subjects to reach quickly for targets while grasping a robotic arm. The arm continuously measured the movements for jerkiness and smoothness and the ability to stay on target, called "aiming."
While initial aiming was not dramatically disturbed in patients with HD, all of these individuals and several of the asymptomatic patients displayed unusual jerkiness as the movements progressed. These results suggest that HD movements often begin normally, but become jerky and irregular at some point during their course because of impaired error feedback, says Maurice Smith, a doctoral student in Johns Hopkins' Department of Biomedical Engineering.
The significance of these findings may be relevant to diseases other than Huntington's, adds Dr. Ross. "In terms of genetic disorders [this] is quite important. Huntington's disease has been the prototype for genetic diseases. We need to develop a whole way of approaching genetic diseases and their onset. HD is presenting a model for doing that." — Donalee Moulton, Halifax
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