Cherry-red spot myoclonus syndrome and alpha-neuraminidase deficiency: neurophysiological, pharmacological and biochemical study in an adult.

A 22 year old patient with non-familial progressive myoclonus, macular cherry-red spot, moderate cerebellar syndrome and normal intelligence is described. The myoclonus began at the age of 18 years. Focal myoclonus could easily be elicited by voluntary and passive movements, and by touch and electrical stimulation of median nerve. Somatosensory evoked potentials showed a high voltage early component. Jerk-locked averaging of the EEG preceding action myoclonus detected an otherwise hidden, time-related, EEG spike. The myoclonus responded partially but clearly to L-5 hydroxytryptophan plus carbidopa treatment. Biochemical study showed an alpha-neuraminidase deficiency in cultured fibroblasts: the decrease in this enzyme activity was compared to that found in a patient affected by mucolipidosis III.