Extending diagnostic practices in gyrate atrophy: Enzymatic characterization and the development of an in vitro pyridoxine responsiveness assay.

Autor:	Balfoort BM; Department of Pediatrics, Emma Children's Hospital, Amsterdam UMC, University of Amsterdam, Amsterdam, the Netherlands; Laboratory Genetic Metabolic Diseases, Amsterdam UMC, University of Amsterdam, Amsterdam, the Netherlands; Amsterdam Gastroenterology, Endocrinology and Metabolism, Amsterdam, University of Amsterdam, Amsterdam, the Netherlands; United for Metabolic Diseases, the Netherlands., Pampalone G; Department of Medicine and Surgery, University of Perugia, Perugia, Italy., Ruiter JPN; Laboratory Genetic Metabolic Diseases, Amsterdam UMC, University of Amsterdam, Amsterdam, the Netherlands., Denis SW; Laboratory Genetic Metabolic Diseases, Amsterdam UMC, University of Amsterdam, Amsterdam, the Netherlands., Brands MM; Department of Pediatrics, Emma Children's Hospital, Amsterdam UMC, University of Amsterdam, Amsterdam, the Netherlands; United for Metabolic Diseases, the Netherlands., Timmer C; Department of Endocrinology and Metabolism, Amsterdam UMC, University of Amsterdam, Amsterdam, the Netherlands., Wagenmakers MAEM; Department of Internal Medicine, Center for Lysosomal and Metabolic Diseases, Erasmus MC, Erasmus University Medical Center Rotterdam, Rotterdam, the Netherlands; United for Metabolic Diseases, the Netherlands., Wanders RJA; Laboratory Genetic Metabolic Diseases, Amsterdam UMC, University of Amsterdam, Amsterdam, the Netherlands; United for Metabolic Diseases, the Netherlands., van Karnebeek CD; Department of Pediatrics, Emma Children's Hospital, Amsterdam UMC, University of Amsterdam, Amsterdam, the Netherlands; Emma Center for Personalized Medicine, Amsterdam UMC, Amsterdam, the Netherlands; Amsterdam Gastroenterology, Endocrinology and Metabolism, Amsterdam, University of Amsterdam, Amsterdam, the Netherlands; United for Metabolic Diseases, the Netherlands., Cellini B; Department of Medicine and Surgery, University of Perugia, Perugia, Italy., Houtkooper RH; Laboratory Genetic Metabolic Diseases, Amsterdam UMC, University of Amsterdam, Amsterdam, the Netherlands; Emma Center for Personalized Medicine, Amsterdam UMC, Amsterdam, the Netherlands; Amsterdam Gastroenterology, Endocrinology and Metabolism, Amsterdam, University of Amsterdam, Amsterdam, the Netherlands; United for Metabolic Diseases, the Netherlands., Ferdinandusse S; Laboratory Genetic Metabolic Diseases, Amsterdam UMC, University of Amsterdam, Amsterdam, the Netherlands; Amsterdam Gastroenterology, Endocrinology and Metabolism, Amsterdam, University of Amsterdam, Amsterdam, the Netherlands; United for Metabolic Diseases, the Netherlands. Electronic address: s.ferdinandusse@amsterdamumc.nl.
Jazyk:	angličtina
Zdroj:	Molecular genetics and metabolism [Mol Genet Metab] 2024 Sep-Oct; Vol. 143 (1-2), pp. 108542. Date of Electronic Publication: 2024 Jul 19.
DOI:	10.1016/j.ymgme.2024.108542
Abstrakt:	Gyrate atrophy of the choroid and retina (GACR) is caused by pathogenic biallelic variants in the gene encoding ornithine-δ-aminotransferase (OAT), and is characterized by progressive vision loss leading to blindness. OAT is a pyridoxal-5'-phosphate (PLP) dependent enzyme that is mainly involved in ornithine catabolism, and patients with a deficiency develop profound hyperornithinemia. Therapy is aimed at lowering ornithine levels through dietary arginine restriction and, in some cases, through enhancement of OAT activity via supraphysiological dosages of pyridoxine. In this study, we aimed to extend diagnostic practices in GACR by extensively characterizing the consequences of pathogenic variants on the enzymatic function of OAT, both at the level of the enzyme itself as well as the flux through the ornithine degradative pathway. In addition, we developed an in vitro pyridoxine responsiveness assay. We identified 14 different pathogenic variants, of which one variant was present in all patients of Dutch ancestry (p.(Gly353Asp)). In most patients the enzymatic activity of OAT as well as the rate of [ 14 C]-ornithine flux was below the limit of quantification (LOQ). Apart from our positive control, only one patient cell line showed responsiveness to pyridoxine in vitro, which is in line with the reported in vivo pyridoxine responsiveness in this patient. None of the patients harboring the p.(Gly353Asp) substitution were responsive to pyridoxine in vivo or in vitro. In silico analysis and small-scale expression experiments showed that this variant causes a folding defect, leading to increased aggregation properties that could not be rescued by PLP. Using these results, we developed a diagnostic pipeline for new patients suspected of having GACR. Adding OAT enzymatic analyses and in vitro pyridoxine responsiveness to diagnostic practices will not only increase knowledge on the consequences of pathogenic variants in OAT, but will also enable expectation management for therapeutic modalities, thus eventually improving clinical care. Competing Interests: Declaration of competing interest The authors have no conflicts of interests to declare. (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)
Databáze:	MEDLINE
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