Postural rhythmic muscle bursting activity in Angelman syndrome

Postural impairment is one of the most consistent features of Angelman syndrome. Using multiple-channel electromyography, we studied a lower limb and an upper limb isometric postural task in 14 patients with Angelman syndrome and 18 unimpaired control subjects. Both tasks were associated with synchronous bursts of activity at frequencies of 6-8 s(-1) in all recorded muscles in all patients with Angelman syndrome and none of the control subjects. This pattern was not altered by extra-loading. Electroencephalogram recorded during the upper limb task showed no change in relation to the task. Burst-locked back-averaging of the electroencephalogram showed no spiking before or during the bursts. Various physiological and pathological rhythmic muscle activities have been proposed to be a manifestation of oscillations in the central nervous system and it has been suggested that such oscillations may have a role in the processing of motor commands. The mechanism of the rhythmic muscle bursting activity associated with maintaining posture in patients with Angelman syndrome is not clear, although it could be consistent with cerebellar Purkinje cell dysfunction, either as a pathological feature or as an adaptive process to overcome deficits in motor coordination.