To report a case of myoclonus-epilepsy in a 25-year old patient harbouring a pathologic C9orf72 repeat expansion (C9orf72 RE), and to review literature reports describing the association of C9orf72 RE with myoclonus-epilepsy syndromes.

Hexanucleotide repeat expansions involving C9orf72 are the most common cause of familial and sporadic cases of ALS and FTD. Increasing reports have expanded the clinical phenotypes associated with C9orf72 RE to include movement disorders, electrographic abnormalities, epilepsy, and progressive myoclonus epilepsy (PME). Autosomal dominant cortical tremor, myoclonus and epilepsy (ADCME) is a rare disorder which has not been associated with C9orf72.

Our patient is a 25-year-old man with cognitive difficulties admitted to our epilepsy monitoring unit (EMU) for characterization of “shaking spells” with preserved awareness. He has a strong paternal family history of ALS-FTD. The patient presented at age 17 with brief episodes of whole body jerking, and he later developed rare generalized tonic clonic seizures that were controlled with anti-seizure medication. Background EEG showed generalized 3-4Hz spike and polyspike and wave discharges. Multiple shaking spells during EMU had no electrographic correlate, and are presumed myoclonus. MRI showed mild cerebellar atrophy. Genetic testing revealed C9orf72 RE in the patient and in affected relatives. We review the literature for reports of C9orf72 mutation in patients with epilepsy, myoclonus and myoclonus epilepsy syndrome.

We describe the association of C9orf72 RE with a presentation of myoclonus-epilepsy in our patient. We observe that the epilepsy-myoclonus in our patient may be more similar to ADCME than that of PME, due to age of onset, slow progression, prominence of myoclonus, minor role of epilepsy, and similar molecular pathophysiology.

Molecular genetic testing of C9orf72 gene should be considered in patients with undetermined cause of myoclonus with epilepsy. A unifying classification of myoclonus-epilepsy across PME and ADCME is needed.