title: New MT-ND6 and NDUFA1 mutations in mitochondrial respiratory chain disorders.
abstract: OBJECTIVE
  Mitochondrial respiratory chain disorder (MRCD) is an intractable disease of infants with variable clinical symptoms. Our goal was to identify the causative mutations in MRCD patients.
  
  
  METHODS
  The subjects were 90 children diagnosed with MRCD by enzyme assay. We analyzed whole mitochondrial DNA (mtDNA) sequences. A cybrid study was performed in two patients. Whole exome sequencing was performed for one of these two patients whose mtDNA variant was confirmed as non-pathogenic.
  
  
  RESULTS
  Whole mtDNA sequences identified 29 mtDNA variants in 29 patients (13 were previously reported, the other 13 variants and three deletions were novel). The remaining 61 patients had no pathogenic mutations in their mtDNA. Of the 13 patients harboring unreported mtDNA variants, we excluded seven variants by manual curation. Of the remaining six variants, we selected two Leigh syndrome patients whose mitochondrial enzyme activity was decreased in their fibroblasts and performed a cybrid study. We confirmed that m.14439G>A (MT-ND6) was pathogenic, while m.1356A>G (mitochondrial 12S rRNA) was shown to be a non-pathogenic polymorphism. Exome sequencing and a complementation study of the latter patient identified a novel c.55C>T hemizygous missense mutation in the nuclear-encoded gene NDUFA1.
  
  
  CONCLUSIONS
  Our results demonstrate that it is important to perform whole mtDNA sequencing rather than only typing reported mutations. Cybrid assays are also useful to diagnose the pathogenicity of mtDNA variants, and whole exome sequencing is a powerful tool to diagnose nuclear gene mutations as molecular diagnosis can provide a lead to appropriate genetic counseling.
authors.affiliation: Division of Functional Genomics & Systems Medicine, Research Center for Genomic Medicine, Saitama Medical University Hidaka, Japan ; Department of Otolaryngology-Head and Neck Surgery, Kobe University Graduate School of Medicine Kobe, Japan.
authors.forename: Natsumi
authors.initials: N
authors.lastname: Uehara
authors.affiliation: Department of Pediatrics, Jichi Medical University Shimotsuke, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Mori
authors.affiliation: Division of Functional Genomics & Systems Medicine, Research Center for Genomic Medicine, Saitama Medical University Hidaka, Japan.
authors.forename: Yoshimi
authors.initials: Y
authors.lastname: Tokuzawa
authors.affiliation: Division of Functional Genomics & Systems Medicine, Research Center for Genomic Medicine, Saitama Medical University Hidaka, Japan.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Mizuno
authors.affiliation: Division of Functional Genomics & Systems Medicine, Research Center for Genomic Medicine, Saitama Medical University Hidaka, Japan.
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Tamaru
authors.affiliation: Division of Functional Genomics & Systems Medicine, Research Center for Genomic Medicine, Saitama Medical University Hidaka, Japan ; Division of Translational Research, Research Center for Genomic Medicine, Saitama Medical University Hidaka, Japan.
authors.forename: Masakazu
authors.initials: M
authors.lastname: Kohda
authors.affiliation: Division of Functional Genomics & Systems Medicine, Research Center for Genomic Medicine, Saitama Medical University Hidaka, Japan.
authors.forename: Yohsuke
authors.initials: Y
authors.lastname: Moriyama
authors.affiliation: Division of Functional Genomics & Systems Medicine, Research Center for Genomic Medicine, Saitama Medical University Hidaka, Japan ; Division of Translational Research, Research Center for Genomic Medicine, Saitama Medical University Hidaka, Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Nakachi
authors.affiliation: Division of Translational Research, Research Center for Genomic Medicine, Saitama Medical University Hidaka, Japan.
authors.forename: Nana
authors.initials: N
authors.lastname: Matoba
authors.affiliation: Department of Pediatrics, Faculty of Medicine, Saitama Medical University Moroyama-machi, Japan.
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Sakai
authors.affiliation: Department of Pediatrics, Faculty of Medicine, Saitama Medical University Moroyama-machi, Japan.
authors.forename: Taro
authors.initials: T
authors.lastname: Yamazaki
authors.affiliation: Department of Pediatrics, Faculty of Medicine, Saitama Medical University Moroyama-machi, Japan.
authors.forename: Hiroko
authors.initials: H
authors.lastname: Harashima
authors.affiliation: Department of Metabolism, Chiba Children's Hospital Chiba, Japan.
authors.forename: Kei
authors.initials: K
authors.lastname: Murayama
authors.affiliation: Faculty of Life and Environmental Sciences, University of Tsukuba Tsukuba, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Hattori
authors.affiliation: Faculty of Life and Environmental Sciences, University of Tsukuba Tsukuba, Japan.
authors.forename: Jun-Ichi
authors.initials: J
authors.lastname: Hayashi
authors.affiliation: Department of Pediatrics, Jichi Medical University Shimotsuke, Japan.
authors.forename: Takanori
authors.initials: T
authors.lastname: Yamagata
authors.affiliation: Research Team for Mechanism of Aging, Tokyo Metropolitan Institute of Gerontology Itabashi, Japan.
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Fujita
authors.affiliation: Research Team for Mechanism of Aging, Tokyo Metropolitan Institute of Gerontology Itabashi, Japan.
authors.forename: Masafumi
authors.initials: M
authors.lastname: Ito
authors.affiliation: Department of Genomics for Longevity and Health, Tokyo Metropolitan Institute of Gerontology Itabashi, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Tanaka
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Kobe University Graduate School of Medicine Kobe, Japan.
authors.forename: Ken-Ichi
authors.initials: K
authors.lastname: Nibu
authors.affiliation: Department of Pediatrics, Faculty of Medicine, Saitama Medical University Moroyama-machi, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Ohtake
authors.affiliation: Division of Functional Genomics & Systems Medicine, Research Center for Genomic Medicine, Saitama Medical University Hidaka, Japan ; Division of Translational Research, Research Center for Genomic Medicine, Saitama Medical University Hidaka, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Okazaki