File:Jimd12321-fig-0001-m.webp

English: Simplified scheme of catecholamine synthesis and breakdown in DBH‐deficiency. Figure ​Figure11 depicts the simplified scheme of the biosynthesis and catabolism of catecholamines (dopamine, norepinephrine, and epinephrine), and shows the metabolic block in DBH‐deficiency (black bar). The artificial compound L‐DOPS can bypass this block because it can be converted to norepinephrine using the enzyme AADC. Breakdown of catecholamines can involve multiple steps (dashed arrows) and differs in different body compartments. HVA is the major stable end‐product of dopamine catabolism in cerebrospinal fluid, blood and urine. MHPG is the major end‐product of (nor)epinephrine catabolism in cerebrospinal fluid. NMET and MET are breakdown products of norepinephrine and epinephrine in the peripheral circulation and urine, VMA is the major common end‐product of (nor)epinephrine catabolism. AADC, aromatic l‐amino acid decarboxylase; ADH, alcohol dehydrogenase; DBH, dopamine beta hydroxylase; DHPG, dihydroxyphenylglycol; COMT: catechol‐O‐methyltransferase; HVA, homovanillic acid; L‐DOPA, L‐3,4 dihydroxyphenylalanine; L‐DOPS: l‐threo‐3,4‐dihydroxyphenylserine; MAO, monoamine oxidase; MET, metanephrine; MHPG, 3‐methoxy‐4‐hydroxyphenylglycol; NMET, normetanephrine; PNMT, phenylethanolamine N‐methyltransferase; VMA, vanillylmandelic acid