A Case Report of Myoclonus-Dystonia with Isolated Myoclonus Phenotype and Novel Mutation Successfully Treated with Deep Brain Stimulation.

INTRODUCTION: Myoclonus-dystonia is an inherited disorder characterized by a combination of myoclonic jerks and dystonia. Mutations in the epsilon-sarcoglycan gene (SGCE) represent the main known genetic cause. In the last few years, deep brain stimulation (DBS) has shown significant promise in treating these patients. There is only one report in the literature of a patient with positive SGCE mutation and isolated myoclonus phenotype who has been successfully treated with DBS. CASE PRESENTATION: We present a case of a 16-year-old young man with a history of quick jerks since childhood. They progressed gradually over the years involving the entire body and interfering with most of his daily activities. He had no dystonia. Genetic testing identified a single base deletion in exon 3 of the SGCE gene, considered very likely pathogenic. After unsuccessfully trying several oral medications, he underwent DBS of the globus pallidus internus (GPi). His Unified Myoclonus Rating Scale score during rest and with action improved by 92.8% and 82.6%, respectively. DISCUSSION: The striking effect of DBS on myoclonic jerks confirms the superior benefit of DBS over oral medications. Further study is needed to determine the role of mutation status in predicting DBS response, especially considering that myoclonus-dystonia is genetically heterogeneous. CONCLUSION: Our case confirms the poor response to oral medications and supports the use of GPi DBS for patients with genetically confirmed myoclonus-dystonia and isolated-myoclonus phenotype. In addition, our case represents familial myoclonus-dystonia due to a novel SGCE mutation.

Large deletions account for an increasing number of mutations in SGCE.

Myoclonus-dystonia (M-D) (MIM 159900) is a rare "dystonia plus" syndrome, characterized by rapid myoclonic jerks, predominantly in the neck and upper limbs, in combination with dystonia. Mutations in the gene epsilon-sarcoglycan (SGCE) are known to be responsible for approximately one-third of cases. We screened 21 probands diagnosed with M-D for large deletions who were mutation negative as determined by PCR-direct sequencing. Multiplex PCR and quantification of PCR products was performed using a modified application of denaturing high performance liquid chromatography (dHPLC). We have identified two novel large multiexonic deletions of SGCE, which were confirmed by amplifying and sequencing the deletion breakpoints. Five other families were found to harbor small mutations identified by direct sequencing. Analysis of the region surrounding the deletions demonstrates that both deletions are the result of nonhomologous recombination with homologous end joining. This is only the second report of intragenic deletions with SGCE and it highlights the need to include exonic copy number variation when performing mutational analysis of SGCE.