An RMND1 Mutation Causes Encephalopathy Associated With Multiple Oxidative Phosphorylation Complex Deficiencies and a Mitochondrial Translation Defect

Am J Hum Genet. 2012 Oct 5;91(4):737-43. doi: 10.1016/j.ajhg.2012.08.020. Epub 2012 Sep 27.

Abstract

Mutations in the genes composing the mitochondrial translation apparatus are an important cause of a heterogeneous group of oxidative phosphorylation (OXPHOS) disorders. We studied the index case in a consanguineous family in which two children presented with severe encephalopathy, lactic acidosis, and intractable seizures leading to an early fatal outcome. Blue native polyacrylamide gel electrophoretic (BN-PAGE) analysis showed assembly defects in all of the OXPHOS complexes with mtDNA-encoded structural subunits, and these defects were associated with a severe deficiency in mitochondrial translation. Immunoblot analysis showed reductions in the steady-state levels of several structural subunits of the mitochondrial ribosome. Whole-exome sequencing identified a homozygous missense mutation (c.1250G>A) in an uncharacterized gene, RMND1 (required for meiotic nuclear division 1). RMND1 localizes to mitochondria and behaves as an integral membrane protein. Retroviral expression of the wild-type RMND1 cDNA rescued the biochemical phenotype in subject cells, and siRNA-mediated knockdown of the protein recapitulated the defect. BN-PAGE, gel filtration, and mass spectrometry analyses showed that RMND1 forms a high-molecular-weight and most likely homopolymeric complex (∼240 kDa) that does not assemble in subject fibroblasts but that is rescued by expression of RMND1 cDNA. The p.Arg417Gln substitution, predicted to be in a coiled-coil domain, which is juxtaposed to a transmembrane domain at the extreme C terminus of the protein, does not alter the steady-state level of RMND1 but might prevent protein-protein interactions in this complex. Our results demonstrate that the RMND1 complex is necessary for mitochondrial translation, possibly by coordinating the assembly or maintenance of the mitochondrial ribosome.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Cycle Proteins / genetics*
  • Consanguinity
  • DNA, Mitochondrial / genetics
  • Exome
  • Female
  • Genetic Predisposition to Disease
  • Homozygote
  • Humans
  • Infant, Newborn
  • Intellectual Disability / genetics*
  • Lennox Gastaut Syndrome
  • Membrane Proteins / genetics
  • Mitochondria / genetics*
  • Mitochondrial Diseases / genetics*
  • Mitochondrial Proteins / genetics*
  • Mutation, Missense*
  • Phenotype
  • Protein Biosynthesis*
  • Protein Interaction Domains and Motifs / genetics
  • Ribosomes / genetics
  • Spasms, Infantile / genetics*

Substances

  • Cell Cycle Proteins
  • DNA, Mitochondrial
  • Membrane Proteins
  • Mitochondrial Proteins
  • RMND1 protein, human

Supplementary concepts

  • Epileptic encephalopathy, Lennox-Gastaut type