Enzyme studies in tardive dyskinesia. I. One-year biochemical follow-up.

Over a 1-year period we followed 12 female in-patients with and 13 without persistent tardive dyskinesia. Clinical signs of tardive dyskinesia as well as plasma dopamine-beta-hydroxylase and platelet monoamine oxidase activities remained stable over time in spite of medication changes. Tardive dyskinesia was associated with higher plasma dopamine-beta-hydroxylase and lower monoamine oxidase activities, both initially and at follow-up. In two patients, an apparent elevation in dopamine-beta-hydroxylase activity preceded the onset of clinical dyskinesia, suggesting that elevated plasma dopamine-beta-hydroxylase activity might be a potential risk marker for the development of tardive dyskinesia.