Mutations in MDH2, Encoding a Krebs Cycle Enzyme, Cause Early-Onset Severe Encephalopathy.

Abstract

MDH2 encodes mitochondrial malate dehydrogenase (MDH), which is essential for the conversion of malate to oxaloacetate as part of the proper functioning of the Krebs cycle. We report bi-allelic pathogenic mutations in MDH2 in three unrelated subjects presenting with early-onset generalized hypotonia, psychomotor delay, refractory epilepsy, and elevated lactate in the blood and cerebrospinal fluid. Functional studies in fibroblasts from affected subjects showed both an apparently complete loss of MDH2 levels and MDH2 enzymatic activity close to null. Metabolomics analyses demonstrated a significant concomitant accumulation of the MDH substrate, malate, and fumarate, its immediate precursor in the Krebs cycle, in affected subjects' fibroblasts. Lentiviral complementation with wild-type MDH2 cDNA restored MDH2 levels and mitochondrial MDH activity. Additionally, introduction of the three missense mutations from the affected subjects into Saccharomyces cerevisiae provided functional evidence to support their pathogenicity. Disruption of the Krebs cycle is a hallmark of cancer, and MDH2 has been recently identified as a novel pheochromocytoma and paraganglioma susceptibility gene. We show that loss-of-function mutations in MDH2 are also associated with severe neurological clinical presentations in children.

• Authors: Samira Ait-El-Mkadem, Manal Dayem-Quere, Mirjana Gusic, Annabelle Chaussenot, Sylvie Bannwarth, Bérengère François, Emmanuelle C Genin, Konstantina Fragaki, Catharina L M Volker-Touw, Christelle Vasnier, Valérie Serre, Koen L I van Gassen, Françoise Lespinasse, Susan Richter, Graeme Eisenhofer, Cécile Rouzier, Fanny Mochel, Anne De Saint-Martin, Marie-Thérèse Abi Warde, Monique G M de Sain-van der Velde, Judith J M Jans, Jeanne Amiel, Ziga Avsec, Christian Mertes, Tobias B Haack, Tim Strom, Thomas Meitinger, Penelope E Bonnen, Robert W Taylor, Julien Gagneur, Peter M van Hasselt, Agnès Rötig, Agnès Delahodde, Holger Prokisch, Sabine A Fuchs, Véronique Paquis-Flucklinger
• Journal: American journal of human genetics (Am J Hum Genet) Vol. 100 Issue 1 Pg. 151-159 (Jan 05 2017) ISSN: 1537-6605 [Electronic] United States
• PMID: 27989324 (Publication Type: Journal Article)
• Copyright: Copyright © 2017 The Author(s). Published by Elsevier Inc. All rights reserved.

Chemical References

• Fumarates
• Malates
• malic acid
• fumaric acid
• MDH2 protein, human
• Malate Dehydrogenase

Topics

• Age of Onset
• Alleles
• Amino Acid Sequence
• Brain Diseases (genetics)
• Child
• Child, Preschool
• Citric Acid Cycle (genetics)
• Fibroblasts (enzymology, metabolism)
• Fumarates (metabolism)
• Genetic Complementation Test
• Humans
• Infant
• Infant, Newborn
• Malate Dehydrogenase (chemistry, genetics, metabolism)
• Malates (metabolism)
• Male
• Metabolomics
• Models, Molecular
• Mutation