Myoclonic Dystonia: A Common Phenomenology in the Pleomorphic Movements of Angelman Syndrome

Angelman syndrome (AS) is a neurodevelopmental disorder characterized by developmental delay, intellectual disability, a sociable demeanor, and abnormal movements. People with AS often exhibit multiple types of abnormal movements, including nonepileptic myoclonus, tremor, and dystonia, which hamper attempts to identify phenomenology and appropriate treatments.

We sought to better clarify movement disorder phenomenology in AS to aid in diagnostic clarity and treatment identification.

Caregivers of people with AS completed a survey focused on abnormal movements in AS and submitted video examples of the movements, when possible. The video data were evaluated by a team of 10 movement disorder experts.

Survey data were obtained for 47 subjects, of whom 20 had accompanying video data; 33% of subjects reported 3 or more abnormal movements, complicating the evaluation of the survey data. Expert review of video data demonstrated 9 people with myoclonus, 9 with dystonia, and 3 with tremor. Five people had both myoclonus and dystonia, and 1 had both tremor and dystonia. Three people demonstrated stereotypy, one of which also had a focal seizure. Dystonia onset averaged 18.1 years. Fever, constipation, and menses were the most notable triggers. According to caregivers, only 4 treatments, clonazepam, diazepam, lorazepam, and trihexyphenidyl, resulted in improvement in dystonic symptoms.

These data reinforce that dystonia is a common finding in people with AS, often in combination with myoclonus. The identification of both isolated dystonia and myoclonic dystonia in people with AS may suggest therapeutic options that heretofore may not have been widely considered.