CASE REPORT article
Front. Neurosci.
Sec. Autonomic Neuroscience
A Possible Novel Adult-Onset, Progressive MAO-A Hypofunction
Provisionally accepted
- 1independent researcher, Edinburgh, United Kingdom
- 2Complex Autonomic Center, Mountlake Terrace, WA, United States
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We describe the clinical presentation, pathophysiology, and successful treatment of a previously undocumented adult onset, progressive form of monoamine oxidase A hypofunction. The patient experienced progressive symptoms consistent with excess intracellular noradrenaline in the sympathetic nervous system and with a reduced ability to metabolize tyramine - both associated with low monoamine oxidase A activity. The nature of the pathophysiology was then tested first by fractionated plasma catecholamine assays, performed at baseline and again using entacapone challenge to suppress catechol-O-methyltransferase function. Plasma noradrenaline levels are unaffected by entacapone in healthy adults, due to monoamine oxidase A activity. This was followed by a direct measurement of plasma catechols (specifically metabolites of norepinephrine and dopamine), to compare their respective levels and ratios to known cases of X-linked monoamine oxidase A microdeletion. Under the entacapone challenge, the patient's plasma noradrenaline increased by 89%, consistent with monoamine oxidase A hypofunction. When repeated with daily rasagiline administration, the increase fell to 14%. Further challenges showed a variable but consistent increase under entacapone. Direct measurement of catechols measurement showed that levels of dihydroxyphenylglycol, a metabolite of norepinephrine via monoamine oxidase A, and 3,4-dihydroxyphenylacetic acid, a metabolite of dopamine via monoamine oxidase A, were significantly below reference range, consistent with reduced monoamine oxidase A activity. Treatment consistent with the hypothesis consisted of rasagiline or selegiline combined with carvedilol. This treatment relieved all symptoms.
Keywords: Carvedilol, hypofunction, MAO-A, Monoamine oxidase A, Norepinephrine, plasma catechols, rasagiline
Received: 01 Dec 2025; Accepted: 03 Feb 2026.
Copyright: © 2026 Berteau and Armitano. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Stefan Berteau
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