Novel SGCE Mutation in a Patient With Myoclonus-Dystonia: A Case Report

Abstract

Objectives: Characterize the presentation, workup, and management of SGCE myoclonus-dystonia, a rare genetic condition, in a patient with atypical presenting symptoms and no family history of movement abnormalities.

Methods: A woman with myoclonus and dystonia was identified based on clinical history and physical examination. Workup was conducted to determine the cause of her symptoms, including whole-exome sequencing. Myoclonus-dystonia is associated with more than 100 distinct mutations in MYC/DYT-SGCE that account for only half of the total myoclonus-dystonia patients. As such, this case required intensive genetic analyses rather than screening only for a small subset of well-characterized mutations.

Results: Childhood onset myoclonus and worsening dystonia with age were identified in a young woman. She underwent screening for common causes of twitching movements, followed by whole-exome sequencing which identified a de novo novel variant in the SGCE gene, resulting in a diagnosis of SGCE myoclonus-dystonia.

Discussion: Myoclonus-dystonia should be considered in patients with symptoms of head and upper extremity myoclonus early in life, especially with co-occurring dystonia, even in the absence of a family history of similar symptoms. Diagnosis of this condition should take place using sequencing, as new mutations continue to be discovered.

Figure. Pedigree of Patient With SGCE Myoclonus-Dystonia

The proband (III-3) developed startle myoclonus and dystonia of the legs and hands at approximately age 10 years, which worsened over time. No other individuals in the family were known to have similar symptoms, and neither parent was a carrier of the identified mutation. The proband's father (II-1) has an unknown family history due to adoption. Unrelated conditions in the family include epilepsy in the maternal grandmother (I-2) and sarcoid in the father (II-1).