Dopa Decarboxylase in Medullary Carcinoma of the Thyroid

Abstract

Aromatic amino acid decarboxylase (dopa decarboxylase) is thought to be a constituent of the thyroid C-cell. Thyroid tumors from members of a family with a strong history of medullary thyroid carcinoma were found to have 30 to 90 times higher activity of dopa decarboxylase than in the surrounding normal thyroid tissue. The dopa decarboxylase activity in the tumor resembled that in pheochromocytoma in its behavior to various substrates and inhibitors. Other decarboxylase enzymes, histidine and ornithine decarboxylase, were not detectable in either tumor or normal thyroid. Tyrosine hydroxylase and tryptophan hydroxylase activities, although present, were not markedly elevated. Histaminase activity, which has previously been shown to be present in this tumor, was high in all samples of tumor. These results demonstrate that dopa decarboxylase may occur in a C-cell tumor as well as in thyroid C-cells. (N Engl J Med 289:545–548, 1973)