FUS-ALS presenting with myoclonic jerks in a 17-year-old man

Fused in sarcoma-related amyotrophic lateral sclerosis (FUS-ALS) accounts for 4% of all familial motor neurone disease, but has a much higher incidence in juvenile ALS. We present a case of a 17-year-old British man with rapidly progressive bulbar and respiratory failure. On examination he had weak periocular muscles, neck flexion weakness, and a wasted, fasciculating and weak tongue. There were no sensory, cerebellar, or extrapyramidal features but he had frequent myoclonic jerks of the limbs. Routine bloods were normal and an MRI of the neuroaxis as well as CT chest, abdomen and pelvis were unremarkable. NCS/EMG was consistent with anterior horn cell disorder and EEG showed multiple paroxysmal generalized spike-wave discharges. DNA sequencing demonstrated that he was heterozygous for the c.1483C>T pathogenic nonsense mutation in exon 14 of the FUS gene, consistent with ALS6. This is the first reported case of FUS-ALS presenting with prominent myoclonus.