Objective: To clarify the clinical and neurophysiologic spectrum of myoclonus-dystonia patients with mutations of the SGCE gene.
Methods: We prospectively studied 41 consecutive patients from 22 families with documented mutations of the SGCE gene. The patients had a standardized interview, neurologic examination, and detailed neurophysiologic examination, including surface polymyography, long-loop C-reflex studies, and EEG jerk-locked back averaging.
Results: We noted a homogeneous electrophysiologic pattern of myoclonus of subcortical origin with short jerks (mean 95 msec, range 25 to 256 msec) at rest, during action, and during posture; there were no features of cortical hyperexcitability (specifically no abnormal C-reflex response and no short-latency premyoclonic potential on back-averaging studies). Myoclonus was either isolated or associated with mild to moderate dystonia, and predominated in the neck/trunk or proximal upper limbs in most cases. We found that 22% of the patients had a spontaneous improvement in their dystonia before reaching adulthood and that hypotonia can occasionally be a presenting symptom of the disorder.
Conclusion: We describe the myoclonus in patients with mutations in the SGCE gene and characterize the electrophysiologic pattern of this myoclonus. This pattern may help to improve the sensitivity of molecular tests and to define homogeneous populations suitable for inclusion in therapeutic trials.