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Biallelic variants in LARS2 and KARS cause deafness and (ovario)leukodystrophy
Marjo S van der Knaap1, Marianna Bugiani2, Marisa I Mendes2
1From the Departments of Child Neurology (M.S.v.d.K., M. Breur) and Neuropathology (M. Bugiani, M. Breur), and Metabolic Unit, Department of Clinical Chemistry (M.I.M., D.E.C.S., G.S.S.), Amsterdam University Medical Centers and Amsterdam Neuroscience; Department of Functional Genomics (M.S.v.d.K.), Center for Neurogenomics and Cognitive Research, VU University, Amsterdam, the Netherlands; Genetic Metabolic Disorders Research Unit (L.G.R., J. Christodoulou), The Children's Hospital at Westmead, and Discipline of Child and Adolescent Health, Sydney Medical School, University of Sydney, NSW, Australia; Architecture et Réactivité de l'ARN (J.R.-T., M.F.), UPR 9002, Université de Strasbourg, CNRS, Strasbourg, France; Institute for Molecular Bioscience (J. Crawford, C.S.), University of Queensland, St. Lucia, Queensland, Australia; Department of Neurology (J.v.G.), Radboud University Medical Center, Donders Institute for Brain, Cognition and Behaviour, Nijmegen; Department of Clinical Genetics (M.S.), Radboud University Medical Center, Nijmegen, the Netherlands; Departement Génétique Médicale (M.W.), Maladies Rares et Médecine Personnalisée, Hôpital Arnaud de Villeneuve, CHRU de Montpellier, France; Department of Clinical Genetics (Q.W.), Amsterdam University Medical Centers, the Netherlands; UF Innovation en Diagnostic Génomique des Maladies Rares (F.T.M.-T.), Centre Hospitalier Universitaire de Dijon, France; Radboud Center for Mitochondrial Medicine (R.J.R.), Translational Metabolic Laboratory, Department of Pediatrics, Radboud University Medical Center, Nijmegen, the Netherlands; Illumina Inc. (R.J.T.), San Diego, CA; AP-HP (B.K., F.M.), La Pitié-Salpêtrière University Hospital, Department of Genetics, Paris; INSERM U 1127 (B.K., C.D., F.M.), CNRS UMR 7225, Sorbonne Universités, UPMC Univ Paris 06 UMR S 1127, Institut du Cerveau et de la Moelle épinière, ICM, Paris, France; Murdoch Children's Research Institute (J. Christodoulou, C.S.), Parkville, Victoria, Australia; Department of Paediatrics (J. Christodoulou), University of Melbourne, Australia; Institute of Human Genetics (C.D.), University Hospital Essen, University Duisburg-Essen, Germany; and Sorbonne Universités (F.M.), Neurometabolic Clinical Research Group, Paris, France. ms.vanderknaap@vumc.nl.
Objective:
To describe the leukodystrophy caused by pathogenic variants in LARS2 and KARS, encoding mitochondrial leucyl transfer RNA (tRNA) synthase and mitochondrial and cytoplasmic lysyl tRNA synthase, respectively.
Methods:
We composed a group of 5 patients with leukodystrophy, in whom whole-genome or whole-exome sequencing revealed pathogenic variants in LARS2 or KARS. Clinical information, brain MRIs, and postmortem brain autopsy data were collected. We assessed aminoacylation activities of purified mutant recombinant mitochondrial leucyl tRNA synthase and performed aminoacylation assays on patients' lymphoblasts and fibroblasts.
Results:
Patients had a combination of early-onset deafness and later-onset neurologic deterioration caused by progressive brain white matter abnormalities on MRI. Female patients with LARS2 pathogenic variants had premature ovarian failure. In 2 patients, MRI showed additional signs of early-onset vascular abnormalities. In 2 other patients with LARS2 and KARS pathogenic variants, magnetic resonance spectroscopy revealed elevated white matter lactate, suggesting mitochondrial disease. Pathology in one patient with LARS2 pathogenic variants displayed evidence of primary disease of oligodendrocytes and astrocytes with lack of myelin and deficient astrogliosis. Aminoacylation activities of purified recombinant mutant leucyl tRNA synthase showed a 3-fold loss of catalytic efficiency. Aminoacylation assays on patients' lymphoblasts and fibroblasts showed about 50% reduction of enzyme activity.
Conclusion:
This study adds LARS2 and KARS pathogenic variants as gene defects that may underlie deafness, ovarian failure, and leukodystrophy with mitochondrial signature. We discuss the specific MRI characteristics shared by leukodystrophies caused by mitochondrial tRNA synthase defects. We propose to add aminoacylation assays as biochemical diagnostic tools for leukodystrophies.
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