Scientists are asking the question, What is a "normal" brain? The results of a research study published in this month's Annals of Neurology demonstrate that some of the apparently normal relatives of patients with neurological disease in fact have abnormal brain patterns.
The researchers studied brain images of patients with an inherited form of the movement disorder dystonia, as well as images of their relatives who have the same genetic defect but do not have the disease. All the study subjects who had the genetic defect, even those who tested "normal" on neurological tests, exhibited the same abnormal pattern of brain activity.
Dystonia is a movement disorder characterized by prolonged muscle contractions that can be as mild as writer's cramp or as severe as contortions that affect the whole body and confine the sufferer to a wheelchair. Some dystonias are caused by injuries to brain areas that control movement, and others have a genetic cause, often appearing in childhood and getting progressively worse.
One subset of dystonia patients has a clearly defined defect in a gene called DYT-1. Although it is not known why this gene defect leads to dystonia, scientists have learned that many people appear normal on routine neurological tests even though they carry the gene defect.
Using positron emission tomography (PET), researchers at North Shore University Hospital in Manhasset, New York, and at Columbia Presbyterian Medical Center in New York City, took a closer look at the brains of DYT-1 dystonia patients and their "normal" relatives who carried the defective gene. They discovered that, compared to control subjects who did not have the gene defect, both of these groups had abnormal patterns of brain activity confined to the same brain networks.
"That's a fascinating thing because it opens the big issue as to whether there are a lot of people walking around in society that we view as 'normal' who may actually have gene-specific abnormalities of brain function," said David Eidelberg, M.D., director of the Functional Brain Imaging Laboratory at North Shore University Hospital, and lead author of the report.
In fact, says Eidelberg, more sophisticated neurological tests may turn up abnormalities in the motor behavior of these "normal" people. Preliminary evidence from a follow-up study suggests that they show subtle abnormalities when tested on complex movement tasks.
In addition to the network of brain regions common to all the DYT-1 carriers, the researchers identified a second network found only in the dystonia patients and only when they were experiencing muscular contractions.
"The big question is why do some have the second network," said Eidelberg. "There may be other genes involved, or there may be environmental causes."
The researchers will now try to refine their understanding of these brain networks, and perhaps approach the question of how these two networks relate to the symptoms of dystonia.
Eidelberg also predicts that the study will prompt researchers studying other inherited diseases to look more closely at individuals who carry defective genes but do not appear to manifest any disease. In a more general sense, he and his colleagues hope that by identifying distinctive brain networks in neurologically normal persons, they can add to the understanding of how genes affect human behavior.
Other authors of the study were James R. Moeller, Ph.D., of the Columbia College of Physicians and Surgeons; Angelo Antonini, M.D., Ph.D., Ken Kazumata, M.D., Toshitaka Nakamura, M.D., Vijay Dhawan, Ph.D., and Phoebe Spetsieris, Ph.D., of the North Shore University Hospital and the New York University School of Medicine; Deborah DeLeon, M.S., and Susan B. Bressman, M.D., of Beth Israel Medical Center; and Stanley Fahn, M.D., of the Neurological Institute in New York.
Materials provided by American Neurological Association. Note: Content may be edited for style and length.
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