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Am J Hum Genet. 2019 Sep 5;105(3):534-548. doi: 10.1016/j.ajhg.2019.07.015. Epub 2019 Aug 15.

Bi-allelic GOT2 Mutations Cause a Treatable Malate-Aspartate Shuttle-Related Encephalopathy.

Author information

1
Departments of Pediatrics & Clinical Genetics, Emma Children's Hospital, Amsterdam University Medical Centres, Amsterdam Gastro-enterology and Metabolism, University of Amsterdam, 1105 AZ Amsterdam, the Netherlands; Department of Pediatrics / Medical Genetics, BC Children's Hospital Research Institute, Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, BC V5Z 4H4, Canada; On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Amalia Children's Hospital, Department of Pediatrics, Radboud University Medical Centre, 6525 GA Nijmegen, the Netherlands. Electronic address: c.d.vankarnebeek@amsterdamumc.nl.
2
On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Department of Genetics, University Medical Center Utrecht, 3584 EA Utrecht, the Netherlands.
3
Zebrafish Centre for Advanced Drug Discovery, Keenan Research Centre for Biomedical Science, Li Ka Sheng Knowledge Institute, St. Michael's Hospital, Toronto, ON M5B 1T8, Canada; Department of Medicine, Physiology and LMP & Institute of Medical Science, University of Toronto, Toronto, ON M5G 2C4, Canada.
4
Departments of Biochemistry, Molecular Biology and Medical Genetics, Cumming School of Medicine, University of Calgary, Calgary, AB T2N 4N1, Canada; Alberta Children's Hospital Research Institute, University of Calgary, Calgary, AB T2N 4N1, Canada.
5
Department Neurosciences and Pediatric, Howard Hughes Medical Institute, University of California; Rady Children's Institute for Genomic Medicine, San Diego, CA 92093, USA.
6
Department of Molecular Medicine and Al Jawhara Center for Molecular Medicine, Genetics and Inherited Diseases, College of Medicine and Medical Sciences, Arabian Gulf University, Postal Code 328, Bahrain.
7
Zebrafish Centre for Advanced Drug Discovery, Keenan Research Centre for Biomedical Science, Li Ka Sheng Knowledge Institute, St. Michael's Hospital, Toronto, ON M5B 1T8, Canada.
8
Clinical Genetics Department, Human Genetics and Genome Research Division, National Research Centre, Cairo 12311, Egypt.
9
Centre for Molecular Medicine and Therapeutics, Department of Medical Genetics, BC Children's Hospital Research Institute, University of British Columbia, Vancouver, BC V5Z 4H4, Canada.
10
Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, BC V6T 1Z3, Canada; BC Children's Hospital Research Institute, Vancouver, BC V5Z 4H4, Canada.
11
Laboratory Genetic Metabolic Diseases, Department of Clinical Chemistry, Amsterdam University Medical Centres, University of Amsterdam, Amsterdam Gastro-enterology and Metabolism, 1105 AZ Amsterdam, the Netherlands.
12
CHU Sainte-Justine Research Center, Montreal, QC H3T 1C5, Canada.
13
Department of Neuroscience & Mental Health, The Hospital for Sick Children & Department of Physiology, University of Toronto, Toronto, ON M5G 1X8, Canada.
14
On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Department of Laboratory Medicine, Translational Metabolic Laboratory, Radboud University Medical Centre, 6525 GA Nijmegen, the Netherlands.
15
On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Amalia Children's Hospital, Department of Pediatrics, Radboud University Medical Centre, 6525 GA Nijmegen, the Netherlands.
16
Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, BC V6T 1Z3, Canada.
17
On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Department of Laboratory Medicine, Translational Metabolic Laboratory, Radboud University Medical Centre, 6525 GA Nijmegen, the Netherlands; Radboud Center for Mitochondrial Medicine, Department of Pediatrics, Radboud University Medical Centre, 6525 GA Nijmegen, the Netherlands.
18
On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Department of Laboratory Medicine, Translational Metabolic Laboratory, Radboud University Medical Centre, 6525 GA Nijmegen, the Netherlands; Amalia Children's Hospital, Department of Pediatrics, Radboud University Medical Centre, 6525 GA Nijmegen, the Netherlands; Radboud Center for Mitochondrial Medicine, Department of Pediatrics, Radboud University Medical Centre, 6525 GA Nijmegen, the Netherlands.
19
On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Laboratory Genetic Metabolic Diseases, Department of Clinical Chemistry, Amsterdam University Medical Centres, University of Amsterdam, Amsterdam Gastro-enterology and Metabolism, 1105 AZ Amsterdam, the Netherlands.
20
On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Department of Laboratory Medicine, Translational Metabolic Laboratory, Radboud University Medical Centre, 6525 GA Nijmegen, the Netherlands. Electronic address: ron.wevers@radboudumc.nl.

Abstract

Early-infantile encephalopathies with epilepsy are devastating conditions mandating an accurate diagnosis to guide proper management. Whole-exome sequencing was used to investigate the disease etiology in four children from independent families with intellectual disability and epilepsy, revealing bi-allelic GOT2 mutations. In-depth metabolic studies in individual 1 showed low plasma serine, hypercitrullinemia, hyperlactatemia, and hyperammonemia. The epilepsy was serine and pyridoxine responsive. Functional consequences of observed mutations were tested by measuring enzyme activity and by cell and animal models. Zebrafish and mouse models were used to validate brain developmental and functional defects and to test therapeutic strategies. GOT2 encodes the mitochondrial glutamate oxaloacetate transaminase. GOT2 enzyme activity was deficient in fibroblasts with bi-allelic mutations. GOT2, a member of the malate-aspartate shuttle, plays an essential role in the intracellular NAD(H) redox balance. De novo serine biosynthesis was impaired in fibroblasts with GOT2 mutations and GOT2-knockout HEK293 cells. Correcting the highly oxidized cytosolic NAD-redox state by pyruvate supplementation restored serine biosynthesis in GOT2-deficient cells. Knockdown of got2a in zebrafish resulted in a brain developmental defect associated with seizure-like electroencephalography spikes, which could be rescued by supplying pyridoxine in embryo water. Both pyridoxine and serine synergistically rescued embryonic developmental defects in zebrafish got2a morphants. The two treated individuals reacted favorably to their treatment. Our data provide a mechanistic basis for the biochemical abnormalities in GOT2 deficiency that may also hold for other MAS defects.

KEYWORDS:

EC 2.6.1.1.; GOT2; aspartate aminotransferase; encephalopathy; inborn error of metabolism; malate-aspartate shuttle; mitochondriopathy; pyridoxine responsive epilepsy; redox imbalance; treatment

PMID:
31422819
PMCID:
PMC6732527
[Available on 2020-03-05]
DOI:
10.1016/j.ajhg.2019.07.015

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