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Knerr I, Colombo R, Urquhart J, Morais A, Merinero B, Oyarzabal A, Pérez B, Jones SA, Perveen R, Preece MA, Rogers Y, Treacy EP, Mayne P, Zampino G, MacKinnon S, Wassmer E, Yue WW, Robinson I, Rodríguez-Pombo P, Olpin SE, Banka S. Expanding the genetic and phenotypic spectrum of branched-chain amino acid transferase 2 deficiency. J Inherit Metab Dis 2019; 42:809-817. [PMID: 31177572 DOI: 10.1002/jimd.12135] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/14/2019] [Revised: 06/04/2019] [Accepted: 06/07/2019] [Indexed: 12/15/2022]
Abstract
The first step in branched-chain amino acid (BCAA) catabolism is catalyzed by the two BCAA transferase isoenzymes, cytoplasmic branched-chain amino acid transferase (BCAT) 1, and mitochondrial BCAT2. Defects in the second step of BCAA catabolism cause maple syrup urine disease (MSUD), a condition which has been far more extensively investigated. Here, we studied the consequences of BCAT2 deficiency, an ultra-rare condition in humans. We present genetic, clinical, and functional data in five individuals from four different families with homozygous or compound heterozygous BCAT2 mutations which were all detected following abnormal biochemical profile results or familial mutation segregation studies. We demonstrate that BCAT2 deficiency has a recognizable biochemical profile with raised plasma BCAAs and, in contrast with MSUD, low-normal branched-chain keto acids (BCKAs) with undetectable l-allo-isoleucine. Interestingly, unlike in MSUD, none of the individuals with BCAT2 deficiency developed acute encephalopathy even with exceptionally high BCAA levels. We observed wide-ranging clinical phenotypes in individuals with BCAT2 deficiency. While one adult was apparently asymptomatic, three individuals had presented with developmental delay and autistic features. We show that the biochemical characteristics of BCAT2 deficiency may be amenable to protein-restricted diet and that early treatment may improve outcome in affected individuals. BCAT2 deficiency is an inborn error of BCAA catabolism. At present, it is unclear whether developmental delay and autism are parts of the variable phenotypic spectrum of this condition or coincidental. Further studies will be required to explore this.
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Affiliation(s)
- Ina Knerr
- National Centre for Inherited Metabolic Disorders, Temple Street Children's University Hospital, Dublin, Ireland
| | - Roberto Colombo
- Institute of Clinical Biochemistry, Faculty of Medicine, Catholic University of the Sacred Heart, Rome, Italy
- Policlinico Agostino Gemelli, Rome, Italy
- Center for the Study of Rare Hereditary Diseases, Niguarda Ca' Granda Metropolitan Hospital, Milan, Italy
| | - Jill Urquhart
- Manchester Centre for Genomic Medicine, St Mary's Hospital, Manchester University NHS Foundation Trust, Health Innovation Manchester, Manchester, UK
| | - Ana Morais
- Centro de Diagnostico de Enfermedades Moleculares, Departamento de Biologia Molecular, Centro de Biologia Molecular Severo Ochoa, Centro de Investigacion Biomedica en Red de Enfermedades Raras, Universidad Autonoma de Madrid, Spain
| | - Begona Merinero
- Centro de Diagnostico de Enfermedades Moleculares, Departamento de Biologia Molecular, Centro de Biologia Molecular Severo Ochoa, Centro de Investigacion Biomedica en Red de Enfermedades Raras, Universidad Autonoma de Madrid, Spain
| | - Alfonso Oyarzabal
- Centro de Diagnostico de Enfermedades Moleculares, Departamento de Biologia Molecular, Centro de Biologia Molecular Severo Ochoa, Centro de Investigacion Biomedica en Red de Enfermedades Raras, Universidad Autonoma de Madrid, Spain
| | - Belén Pérez
- Centro de Diagnostico de Enfermedades Moleculares, Departamento de Biologia Molecular, Centro de Biologia Molecular Severo Ochoa, Centro de Investigacion Biomedica en Red de Enfermedades Raras, Universidad Autonoma de Madrid, Spain
| | - Simon A Jones
- Manchester Centre for Genomic Medicine, St Mary's Hospital, Manchester University NHS Foundation Trust, Health Innovation Manchester, Manchester, UK
- Division of Evolution and Genomic Sciences, School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK
| | - Rahat Perveen
- Division of Evolution and Genomic Sciences, School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK
| | - Mary A Preece
- Children's Hospital, Birmingham Women's and Children's NHS Foundation Trust, Birmingham, UK
| | - Yvonne Rogers
- National Centre for Inherited Metabolic Disorders, Temple Street Children's University Hospital, Dublin, Ireland
| | - Eileen P Treacy
- National Centre for Inherited Metabolic Disorders, Temple Street Children's University Hospital, Dublin, Ireland
- Adult Metabolic Service, Mater Misericordiae University Hospital, Dublin, Ireland
| | - Philip Mayne
- Department of Biochemistry, Temple Street Children's University Hospital, Dublin, Ireland
| | - Giuseppe Zampino
- Department of Paediatrics, Catholic University of the Sacred Heart, and Center for Rare Diseases, Policlinico Agostino Gemelli, Rome, Italy
| | - Sabrina MacKinnon
- Structural Genomics Consortium, Nuffield Department of Medicine, University of Oxford, Oxford, UK
| | - Evangeline Wassmer
- Children's Hospital, Birmingham Women's and Children's NHS Foundation Trust, Birmingham, UK
| | - Wyatt W Yue
- Structural Genomics Consortium, Nuffield Department of Medicine, University of Oxford, Oxford, UK
| | - Ian Robinson
- Department of Radiology, Temple Street Children's University Hospital, Dublin, Ireland
| | - Pilar Rodríguez-Pombo
- Centro de Diagnostico de Enfermedades Moleculares, Departamento de Biologia Molecular, Centro de Biologia Molecular Severo Ochoa, Centro de Investigacion Biomedica en Red de Enfermedades Raras, Universidad Autonoma de Madrid, Spain
| | - Simon E Olpin
- Department of Clinical Chemistry, Sheffield Children's NHS Foundation Trust, Sheffield Children's Hospital, Sheffield, UK
| | - Siddharth Banka
- Manchester Centre for Genomic Medicine, St Mary's Hospital, Manchester University NHS Foundation Trust, Health Innovation Manchester, Manchester, UK
- Division of Evolution and Genomic Sciences, School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK
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