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  • Updated 05.14.2024
  • Released 03.30.1995
  • Expires For CME 05.14.2027

Monoamine oxidase deficiency



Monoamine oxidase-A deficiency is an X-linked disorder affecting the catabolism of serotonin and the catecholamines. The main symptoms are mild intellectual disability and behavioral abnormalities consisting of excessive, sometimes violent aggression. Diagnosis may be inferred from a finding of elevated urinary concentrations of the monoamine oxidase-A substrates, normetanephrine, 3-methoxytyramine, and tyramine, in combination with reduced amounts of the monoamine oxidase products, vanillylmandelic acid, homovanillic acid, 3-methoxy-4-hydroxyphenolglycol, and 5-hydroxyindoleacetic acid. Monoamine oxidase deficiency has been found as an isolated defect affecting monoamine oxidase A and, in combination with a deletion of the Norrie disease gene, as a combined deficiency of monoamine oxidase A and B or an isolated deficiency of monoamine oxidase B. Confirmation of monoamine oxidase-A deficiency is obtained by measurement of the activity of this enzyme in dexamethasone-stimulated fibroblasts. Combined monoamine oxidase-A and -B deficiency has similar biochemical consequences. Presentation is with intermittent hypotonia, stereotypic hand movements, and developmental delay.

Key points

• Monoamine oxidase deficiency is inherited as an X-linked trait.

• Monoamine oxidase exists in two distinct forms encoded by separate genes, monoamine oxidase-A and monoamine oxidase-B, and each has preferential affinities for biogenic amine and other amine substrates.

• Monoamine oxidase deficiency has been described as isolated monoamine oxidase-A deficiency, as a combined monoamine oxidase-A and B deficiency, as a combined monoamine oxidase-A and B deficiency in association with Norrie disease, and as an isolated monoamine oxidase-B deficiency in association with Norrie disease.

• Individuals with monoamine oxidase deficiency should avoid foods or drugs containing amines.

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