Reduced Plasma Dopamine-β-Hydroxylase Activity in Familial Dysautonomia

Dopamine-β-hydroxylase (DBH), the enzyme that converts dopamine to norepinephrine, was measured in the plasma of 146 normal subjects, 26 patients with familial dysautonomia and 33 parents of patients with this disease. Plasma DBH increased with age in the normal population, reached adult values in the decade from 10 to 19 years of age, and showed no change thereafter in decades up to the age of 40. Plasma DBH was significantly decreased in familial dysautonomia. About 25 per cent of patients with dysautonomia had no detectable plasma DBH activity, and the mothers of patients without plasma DBH had decreased DBH activity. These data are compatible with previous findings of a functional disorder in catecholamine biosynthesis in familial dysautonomia and raise the possibility of a subgroup of “DBH-negative” patients with this disease.