Neurophysiological Markers in Patients With Craniofacial Dystonia and Their Relatives

Overview

This study will use a technique called blink reflex to study and compare how the brain controls muscle movement in patients with craniofacial dystonia, their first-degree relatives, and healthy, normal volunteers. People with dystonia have sustained muscle contractions that cause twisting and repetitive movements or abnormal postures. In focal dystonia, this happens in one area of the body, such as the hand, neck, or face. Three groups of people may be eligible for this study: 1) patients 18 years of age and older with craniofacial dystonia; 2) first-degree relatives of patients with craniofacial dystonia; and 3) normal volunteers matched in age to the patients. Candidates are screened with physical and neurological examinations. Participants undergo a blink reflex study. Patients with dystonia who are receiving botulinum toxin injections must stop the medication 3 months before participating in the study and must stop any other dystonia medications, such as benzodiazepines and anticholinergics, for 12 hours before the study. For the blink reflex procedure, subjects are seated in a comfortable chair with their hands placed on a pillow on their lap. Metal electrodes are taped to the forehead for delivering small electrical shocks that feel like very brief pinpricks. Subjects receive 25 to 50 electrical stimuli, some as single shocks and some in pairs. The electrical activity of muscles that respond to the stimuli is recorded with a computer. The study takes from about 1 to 2 hours.

The objective of this study is to evaluate paired-pulse inhibition of the three responses of the electrically elicited blink reflex (BR) and the eye blink rate (EBR)in patients with craniofacial dystonia and their first degree relatives in order to determine whether abnormalities of inhibition can represent a marker of genetic predisposition for the development of dystonia. It is unclear why some relatives of patients with craniofacial dystonia do not develop dystonic symptoms. One possible explanation is that the development of dystonia is a two-stage process: first, loss of inhibition, which may be genetically determined, and second, exposure to an environmental trigger such as excessive repetitive movements. There is good evidence that focal dystonia is a genetically determined disorder, but the responsible gene remains undetermined. Patients, their first degree relatives and normal volunteers will undergo BR testing using validated electrophysiological tests of recovery cycle. The main outcome measure of the study is impaired inhibition in up to 50% of first degree relatives of patients with focal dystonia which would serve as biologic marker for the carrier state. A second outcome measure is the EBR. In those individuals with this genetic marker of impaired inhibition, future linkage analysis studies could be performed to identify the causative gene.