Specific genetic deficiencies of the A and B isoenzymes of monoamine oxidase are characterized by distinct neurochemical and clinical phenotypes.

Abstract

Monoamine oxidase (MAO) exists as two isoenzymes and plays a central role in the metabolism of monoamine neurotransmitters. In this study we compared the neurochemical phenotypes of previously described subjects with genetically determined selective lack of MAO-A or a lack of both MAO-A and MAO-B with those of two subjects with a previously described X chromosome microdeletion in whom we now demonstrate selective MAO-B deficiency. Mapping of the distal deletion breakpoint demonstrates its location in intron 5 of the MAO-B gene, with the deletion extending proximally into the Norrie disease gene. In contrast to the borderline mental retardation and abnormal behavioral phenotype in subjects with selective MAO-A deficiency and the severe mental retardation in patients with combined MAO-A/MAO-B deficiency and Norrie disease, the MAO-B-deficient subjects exhibit neither abnormal behavior nor mental retardation. Distinct neurochemical profiles characterize the three groups of MAO-deficient patients. In MAO-A-deficient subjects, there is a marked decrease in deaminated catecholamine metabolites and a concomitant marked elevation of O-methylated amine metabolites. These neurochemical changes are only slightly exaggerated in patients with combined lack of MAO-A and MAO-B. In contrast, the only biochemical abnormalities detected in subjects with the MAO-B gene deletion are a complete absence of platelet MAO-B activity and an increased urinary excretion of phenylethylamine. The differences in neurochemical profiles indicate that, under normal conditions, MAO-A is considerably more important than MAO-B in the metabolism of biogenic amines, a factor likely to contribute to the different clinical phenotypes.

• Authors: J W Lenders, G Eisenhofer, N G Abeling, W Berger, D L Murphy, C H Konings, L M Wagemakers, I J Kopin, F Karoum, A H van Gennip, H G Brunner
• Journal: The Journal of clinical investigation (J Clin Invest) Vol. 97 Issue 4 Pg. 1010-9 (Feb 15 1996) ISSN: 0021-9738 [Print] United States
• PMID: 8613523 (Publication Type: Journal Article)

Chemical References

• Catecholamines
• Serotonin
• Monoamine Oxidase

Topics

• Adult
• Blindness (genetics)
• Blood Platelets (chemistry)
• Catecholamines (metabolism)
• Humans
• Intellectual Disability (genetics)
• Male
• Monoamine Oxidase (deficiency)
• Phenotype
• Sequence Deletion
• Serotonin (blood)
• X Chromosome