A neurophysiological study of myoclonus in patients with DYT11 myoclonus‐dystonia syndrome

Mutations in the ?‐sarcoglycan (SGCE) gene have been associated with DYT11 myoclonus‐dystonia syndrome (MDS). The aim of this study was to characterize myoclonus in 9 patients with DYT11‐MDS presenting with predominant myoclonus and mild dystonia by means of neurophysiological techniques. Variously severe multifocal myoclonus occurred in all of the patients, and included short (mean 89.1 ± 13.3 milliseconds) electromyographic bursts without any electroencephalographic correlate, sometimes presenting a pseudo‐rhythmic course. Massive jerks could be evoked by sudden stimuli in 5 patients, showing a “startle‐like” muscle spreading and latencies consistent with a brainstem origin. Somatosensory evoked potentials and long‐loop reflexes were normal, as was silent period and long‐term intracortical inhibition evaluated by means of transcranial magnetic stimulation; however, short‐term intracortical inhibition revealed subtle impairment, and event‐related synchronization (ERS) in the beta band was delayed. Blink reflex recovery was strongly enhanced. Myoclonus in DYT11‐MDS seems to be generated at subcortical level, and possibly involves basal ganglia and brainstem circuitries. Cortical impairment may depend from subcortical dysfunction, but it can also have a role in influencing the myoclonic presentation. The wide distribution of the defective SCGE in DYT11‐MDS may justify the involvement of different brain areas. © 2008 Movement Disorder Society