We report eight cases of genetically proven ULD, with the aim of reassessing the clinical characteristics and natural history of ULD in genetically characterized patients. The eight patients had their first symptoms at mean age of 10.6 years (range: 6-14 years). The main clinical features were action myoclonus, cerebellar ataxia, seizures, and mild intellectual dysfunction. We report three new clinical features of ULD; ocular motor apraxia, dystonia, and rapidly progressive dementia. All patients needed a combination of at least four antimyoclonic drugs, but despite this, all patients were severely disabled by their action myoclonus. After a mean duration of disease of 29.9 years (range: 21-37 years), four patients were walking with aids while another four were wheelchair bound. The clinical phenotypes associated with ULD are more diverse than previously recognized and even though the long term functional outcome and survival have improved, the overall efficacy of antimyoclonic drugs remains unsatisfactory.
2007 Movement Disorder Society