Anna-Kaisa Anttonen1, Taru Hilander1, Tarja Linnankivi1, Pirjo Isohanni1, Rachel L French1, Yuchen Liu1, Miljan Simonović1, Dieter Söll1, Mirja Somer1, Dorota Muth-Pawlak1, Garry L Corthals1, Anni Laari1, Emil Ylikallio1, Marja Lähde1, Leena Valanne1, Tuula Lönnqvist1, Helena Pihko1, Anders Paetau1, Anna-Elina Lehesjoki1, Anu Suomalainen1, Henna Tyynismaa2. 1. From the Department of Medical Genetics, Haartman Institute (A.-K.A., H.T.), Folkhälsan Institute of Genetics and Neuroscience Center (A.-K.A., A.L., A.-E.L.), Research Programs Unit, Molecular Neurology, Biomedicum Helsinki (T.H., P.I., A.L., E.Y., A.-E.L.), University of Helsinki; Departments of Clinical Genetics (A.-K.A.) and Neurology (A.S.), Helsinki University Central Hospital; Department of Pediatric Neurology (T. Linnankivi, P.I., T. Lönnqvist, H.P.), Children's Hospital, University of Helsinki and Helsinki University Central Hospital, Finland; Department of Biochemistry and Molecular Genetics (R.L.F., M. Simonović), University of Illinois at Chicago; Department of Molecular Biophysics and Biochemistry (Y.L., D.S.), Yale University, New Haven, CT; Norio Centre (M. Somer), Department of Medical Genetics, Helsinki, Finland; Turku Centre for Biotechnology (D.M.-P., G.L.C.), University of Turku and Åbo Akademi University; Department of Pediatric Neurology (M.L.), South Karelia Central Hospital, Lappeenranta; Department of Radiology (L.V.), HUS Medical Imaging Center, Helsinki; and Department of Pathology (A.P.), HUSLAB and University of Helsinki, Finland. G.L.C. is currently affiliated with Van't Hoff Institute for Molecular Sciences, University of Amsterdam, the Netherlands. 2. From the Department of Medical Genetics, Haartman Institute (A.-K.A., H.T.), Folkhälsan Institute of Genetics and Neuroscience Center (A.-K.A., A.L., A.-E.L.), Research Programs Unit, Molecular Neurology, Biomedicum Helsinki (T.H., P.I., A.L., E.Y., A.-E.L.), University of Helsinki; Departments of Clinical Genetics (A.-K.A.) and Neurology (A.S.), Helsinki University Central Hospital; Department of Pediatric Neurology (T. Linnankivi, P.I., T. Lönnqvist, H.P.), Children's Hospital, University of Helsinki and Helsinki University Central Hospital, Finland; Department of Biochemistry and Molecular Genetics (R.L.F., M. Simonović), University of Illinois at Chicago; Department of Molecular Biophysics and Biochemistry (Y.L., D.S.), Yale University, New Haven, CT; Norio Centre (M. Somer), Department of Medical Genetics, Helsinki, Finland; Turku Centre for Biotechnology (D.M.-P., G.L.C.), University of Turku and Åbo Akademi University; Department of Pediatric Neurology (M.L.), South Karelia Central Hospital, Lappeenranta; Department of Radiology (L.V.), HUS Medical Imaging Center, Helsinki; and Department of Pathology (A.P.), HUSLAB and University of Helsinki, Finland. G.L.C. is currently affiliated with Van't Hoff Institute for Molecular Sciences, University of Amsterdam, the Netherlands. henna.tyynismaa@helsinki.fi.
Abstract
OBJECTIVE: We aimed to decipher the molecular genetic basis of disease in a cohort of children with a uniform clinical presentation of neonatal irritability, spastic or dystonic quadriplegia, virtually absent psychomotor development, axonal neuropathy, and elevated blood/CSF lactate. METHODS: We performed whole-exome sequencing of blood DNA from the index patients. Detected compound heterozygous mutations were confirmed by Sanger sequencing. Structural predictions and a bacterial activity assay were performed to evaluate the functional consequences of the mutations. Mass spectrometry, Western blotting, and protein oxidation detection were used to analyze the effects of selenoprotein deficiency. RESULTS: Neuropathology indicated laminar necrosis and severe loss of myelin, with neuron loss and astrogliosis. In 3 families, we identified a missense (p.Thr325Ser) and a nonsense (p.Tyr429*) mutation in SEPSECS, encoding the O-phosphoseryl-tRNA:selenocysteinyl-tRNA synthase, which was previously associated with progressive cerebellocerebral atrophy. We show that the mutations do not completely abolish the activity of SEPSECS, but lead to decreased selenoprotein levels, with demonstrated increase in oxidative protein damage in the patient brain. CONCLUSIONS: These results extend the phenotypes caused by defective selenocysteine biosynthesis, and suggest SEPSECS as a candidate gene for progressive encephalopathies with lactate elevation.
OBJECTIVE: We aimed to decipher the molecular genetic basis of disease in a cohort of children with a uniform clinical presentation of neonatal irritability, spastic or dystonic quadriplegia, virtually absent psychomotor development, axonal neuropathy, and elevated blood/CSFlactate. METHODS: We performed whole-exome sequencing of blood DNA from the index patients. Detected compound heterozygous mutations were confirmed by Sanger sequencing. Structural predictions and a bacterial activity assay were performed to evaluate the functional consequences of the mutations. Mass spectrometry, Western blotting, and protein oxidation detection were used to analyze the effects of selenoprotein deficiency. RESULTS: Neuropathology indicated laminar necrosis and severe loss of myelin, with neuron loss and astrogliosis. In 3 families, we identified a missense (p.Thr325Ser) and a nonsense (p.Tyr429*) mutation in SEPSECS, encoding the O-phosphoseryl-tRNA:selenocysteinyl-tRNA synthase, which was previously associated with progressive cerebellocerebral atrophy. We show that the mutations do not completely abolish the activity of SEPSECS, but lead to decreased selenoprotein levels, with demonstrated increase in oxidative protein damage in the patient brain. CONCLUSIONS: These results extend the phenotypes caused by defective selenocysteine biosynthesis, and suggest SEPSECS as a candidate gene for progressive encephalopathies with lactate elevation.
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