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Selenoprotein biosynthesis defect causes progressive encephalopathy with elevated lactate.

Anna-Kaisa Anttonen1, Taru Hilander1, Tarja Linnankivi1

  • 1From 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.

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Genetic mutations in SEPSECS cause severe neurological disorders in children, leading to decreased selenoprotein levels and increased oxidative stress. This research identifies SEPSECS as a key gene for progressive encephalopathies with elevated lactate.

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Area of Science:

  • Neurogenetics
  • Biochemistry
  • Molecular Biology

Background:

  • Neonatal neurological disorders present with severe symptoms like irritability, quadriplegia, and developmental delay.
  • Elevated lactate levels in blood and cerebrospinal fluid (CSF) can indicate mitochondrial dysfunction or metabolic disorders.

Purpose of the Study:

  • To investigate the molecular genetic underpinnings of a rare pediatric neurological condition.
  • To identify the specific gene mutations responsible for the observed clinical phenotype and neuropathology.

Main Methods:

  • Whole-exome sequencing (WES) was employed to identify genetic variants in affected children.
  • Sanger sequencing confirmed identified mutations.
  • Functional assays, including structural predictions and activity assays, assessed the impact of mutations on SEPSECS protein function.
  • Mass spectrometry and Western blotting analyzed selenoprotein levels and oxidative damage in patient brain tissue.

Main Results:

  • Neuropathological findings revealed severe brain abnormalities, including myelin loss and neuronal damage.
  • Compound heterozygous mutations (p.Thr325Ser and p.Tyr429*) in the SEPSECS gene were identified in three families.
  • These mutations impaired O-phosphoseryl-tRNA:selenocysteinyl-tRNA synthase activity, reducing selenoprotein levels and increasing oxidative protein damage in the brain.

Conclusions:

  • The study expands the known spectrum of diseases linked to defects in selenocysteine biosynthesis.
  • SEPSECS is implicated as a candidate gene for progressive encephalopathies characterized by elevated lactate levels.
  • Understanding these genetic defects is crucial for diagnosing and potentially treating severe pediatric neurological conditions.