Identification and prenatal genetic testing of pathogenic variants in a case of myoclonus-dystonia syndrome.

Myoclonus-dystonia syndrome (MDS) is a movement disorder syndrome characterized primarily by myoclonus as the core feature. In this study, we reported a case of MDS with myoclonus as the prominent feature, which was accompanied by learning disability and special face. We then used copy number variation sequencing (CNV-seq), whole exome sequencing (WES) and Sanger sequencing to verify the MDS related genes of the patient and his family members. We found that the patient carried a heterozygous mutation of SGCE gene c.731dup (p.Asn244Lysfs*6) related to MDS, which inherited from his father. It was the first reported new mutation at home and abroad. And we confirmed via prenatal diagnosis that his fetus also had a heterozygous mutation of SGCE gene c.731dup (p.Asn244Lysfs*6). In addition, we also found that there was a 1.40 Mb repeat fragment at p23.1 on chromosome 8 of the patient, which partially overlapped with 8p23.1 repeat syndrome. It is speculated that it may be related to the learning disability and special facial phenotype of the patient, and it was a de novo variant. This study not only clarified the etiology of the patient's myoclonus, but also enriched the genetic variation database of SGCE gene by the newly discovered heterozygous heterozygous site of c.731dup (p.Asn244Lysfs*6) of SGCE gene, which was helpful to improve the clinician's awareness of diagnosis of MDS and provide guidance for the patient's fertility.