Exercise intolerance and developmental delay associated with a novel mitochondrial ND5 mutation.

Hezhi Fang,Yanling Yang,Bin Li,Hao Shi,Jianxin Lu,Yuan Ding,Yao Zhang,Yidong Bai,Xiyuan Li,Dayan Sun,Yanyan Ma,Yupeng Liu,Lijun Shen,Fengjie Li

doi:10.1038/srep10480

Abstract

The aim of this study was to evaluate the contribution of mitochondrial DNA (mtDNA) mutations in oxidative phosphorylation (OXPHOS) deficiency. The complete mitochondrial genomes of 41 families with OXPHOS deficiency were screened for mutations. Mitochondrial functional analysis was then performed in primary and cybrid cells containing candidate mutations identified during the screening. A novel mitochondrial NADH dehydrogenase 5 (ND5) m.12955A > G mutation was identified in a patient with exercise intolerance and developmental delay. A biochemical analysis revealed deficiencies in the activity of complex I (NADH:quinone oxidoreductase) and IV (cytochrome c oxidase) of this patient. Defects in complexes I and IV were confirmed in transmitochondrial cybrid cells containing the m.12955A > G mutation, suggesting that this mutation impairs complex I assembly, resulting in reduced stability of complex IV. Further functional investigations revealed that mitochondria with the m.12955A > G mutation exhibited lower OXPHOS coupling respiration and adenosine triphosphate (ATP) generation. In addition, the cytotoxic effects, determined as reactive oxygen species (ROS) and lactate levels in the present study, increased in the cells carrying a higher m.12955A > G mutant load. In conclusion, we identified m.12955A > G as a mitochondrial disease-related mutation. Therefore, screening of m.12955A > G is advised for the diagnosis of patients with mitochondrial disease.

Highlights

Long-term survey of mitochondrial respiratory chain disorders in Australian children showed that oxidative phosphorylation (OXPHOS) disorders were frequently observed in newborns, with an estimated incidence of 1 in 5,000 and complex I defects accounted for approximately 25–35%3,4 of these cases
Recent studies have shown that approximately 20% of cases of isolated complex I deficiency were caused by mitochondrial DNA (mtDNA) mutations in mitochondrially encoded NADH dehydrogenase (MTND) genes[8]
Samples from 41 patients diagnosed with OXPHOS deficiency and their maternal family members were obtained from Peking University First Hospital (China)

Summary

Introduction

Long-term survey of mitochondrial respiratory chain disorders in Australian children showed that OXPHOS disorders were frequently observed in newborns, with an estimated incidence of 1 in 5,000 and complex I defects accounted for approximately 25–35%3,4 of these cases. All seven mtDNA encoded hydrophobic subunits [mitochondrially encoded NADH dehydrogenase 1–6 and 4L (ND1-ND6 and ND4L)] are core subunits of complex I and form the major complex I membrane arm. Recent studies have shown that approximately 20% of cases of isolated complex I deficiency were caused by mtDNA mutations in mitochondrially encoded NADH dehydrogenase (MTND) genes[8]. Elucidation of the functional effects of pathogenic mtDNA mutations will aid in the genetic diagnosis of patients with complex I deficiency. The reported pathogenic mtDNA mutations m.3697G > A and m.14487T > C were identified in two patients with MELAS and Leigh syndrome, respectively[12,13]. The effects of the m.12955A > G mutation on OXPHOS deficiency was analyzed by assessing mitochondrial respiration, adenosine triphosphate (ATP) content, reactive oxygen species (ROS) levels, and lactate acid levels in addition to complex I assembly and activity

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Conclusion