The compound 3-methoxytyramine, the O-methylated metabolite of dopamine, is useful for the diagnosis of neuroblastoma or dopamine-producing pheochromocytomas and paragangliomas [52] and elevated serum levels are associated with aromatic L-amino-acid decarboxylase deficiency [53]. This evidence concerns the gene DDC and hereditary pheochromocytoma-paraganglioma.