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Mitochondrial Complex III Deficiency Caused by a Homozygous UQCRC2 Mutation Presenting with Neonatal-Onset Recurrent Metabolic Decompensation

Authors


  • Communicated by Daniel Nebert

  • Contract grant sponsors: Ministry of Health, Labor, and Welfare; the Japan Science and Technology Agency; the Strategic Research Program for Brain Sciences; Ministry of Education, Culture, Sports, Science, and Technology of Japan; the Japan Society for the Promotion of Science; 2011 Strategic Research Promotion of Yokohama City University; the Japan Epilepsy Research Foundation; and the Takeda Science Foundation.

Correspondence to: Noriko Miyake, Department of Human Genetics, Yokohama City University Graduate School of Medicine, 3-9 Fukuura, Kanazawa-ku, Yokohama 236-0004, Japan. E-mail: Noriko Miyake: nmiyake@yokohama-cu.ac.jp; or Naomichi Matsumoto, Department of Human Genetics, Yokohama City University Graduate School of Medicine, 3-9 Fukuura, Kanazawa-ku, Yokohama 236-0004, Japan. E-mail: naomat@yokohama-cu.ac.jp

ABSTRACT

Mitochondrial complex III (CIII) deficiency is a relatively rare disease with high clinical and genetic heterogeneity. CIII comprises 11 subunits encoded by one mitochondrial and 10 nuclear genes. Abnormalities of the nuclear genes such as BCS1L and TTC19 encoding mitochondrial assembly factors are well known, but an explanation of the majority of CIII deficiency remains elusive. Here, we report three patients from a consanguineous Mexican family presenting with neonatal onset of hypoglycemia, lactic acidosis, ketosis, and hyperammonemia. We found a homozygous missense mutation in UQCRC2 that encodes mitochondrial ubiquinol–cytochrome c reductase core protein II by whole-exome sequencing combined with linkage analysis. On the basis of structural modeling, the mutation (p.Arg183Trp) was predicted to destabilize the hydrophobic core at the subunit interface of the core protein II homodimer. In vitro studies using fibroblasts from the index patient clearly indicated CIII deficiency, as well as impaired assembly of the supercomplex formed from complexes I, III, and IV. This is the first described human disease caused by a core protein abnormality in mitochondrial CIII.

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