Characterized by a rhythmic branchial myoclonus
(affecting palate, pharynx, larynx, lower face, and neck) resulting in dysphagia,
dysphonia, choking spells, spastic paraparesis (preserved, muscle strength
brisk reflexes, normal sensation), cerebellar ataxia (truncal), nystagmus,
and normal mental status. The age at onset usually is between 30 and 50 years.
The condition is progressive, leading to death or severe disability within 5
to 10 years of onset.