Mutations in COA7 cause spinocerebellar ataxia with axonal neuropathy

Yujiro Higuchi, Ryuta Okunushi, Taichi Hara, Akihiro Hashiguchi, Junhui Yuan, Akiko Yoshimura, Kei Murayama, Akira Ohtake, Masahiro Ando, Yu Hiramatsu, Satoshi Ishihara, Hajime Tanabe, Yuji Okamoto, Eiji Matsuura, Takehiro Ueda, Tatsushi Toda, Sumimasa Yamashita, Kenichiro Yamada, Takashi Koide, Hiroaki YaguchiJun Mitsui, Hiroyuki Ishiura, Jun Yoshimura, Koichiro Doi, Shinichi Morishita, Ken Sato, Masanori Nakagawa, Masamitsu Yamaguchi, Shoji Tsuji, Hiroshi Takashima*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

30 Citations (Scopus)


Several genes related to mitochondrial functions have been identified as causative genes of neuropathy or ataxia. Cytochrome c oxidase assembly factor 7 (COA7) may have a role in assembling mitochondrial respiratory chain complexes that function in oxidative phosphorylation. Here we identified four unrelated patients with recessive mutations in COA7 among a Japanese case series of 1396 patients with Charcot-Marie-Tooth disease (CMT) or other inherited peripheral neuropathies, including complex forms of CMT. We also found that all four patients had characteristic neurological features of peripheral neuropathy and ataxia with cerebellar atrophy, and some patients showed leukoencephalopathy or spinal cord atrophy on MRI scans. Validated mutations were located at highly conserved residues among different species and segregated with the disease in each family. Nerve conduction studies showed axonal sensorimotor neuropathy. Sural nerve biopsies showed chronic axonal degeneration with a marked loss of large and medium myelinated fibres. An immunohistochemical assay with an anti-COA7 antibody in the sural nerve from the control patient showed the positive expression of COA7 in the cytoplasm of Schwann cells. We also observed mildly elevated serum creatine kinase levels in all patients and the presence of a few ragged-red fibres and some cytochrome c oxidase-negative fibres in a muscle biopsy obtained from one patient, which was suggestive of subclinical mitochondrial myopathy. Mitochondrial respiratory chain enzyme assay in skin fibroblasts from the three patients showed a definitive decrease in complex I or complex IV. Immunocytochemical analysis of subcellular localization in HeLa cells indicated that mutant COA7 proteins as well as wild-type COA7 were localized in mitochondria, which suggests that mutant COA7 does not affect the mitochondrial recruitment and may affect the stability or localization of COA7 interaction partners in the mitochondria. In addition, Drosophila COA7 (dCOA7) knockdown models showed rough eye phenotype, reduced lifespan, impaired locomotive ability and shortened synaptic branches of motor neurons. Our results suggest that loss-of-function COA7 mutation is responsible for the phenotype of the presented patients, and this new entity of disease would be referred to as spinocerebellar ataxia with axonal neuropathy type 3.

Original languageEnglish
Pages (from-to)1622-1636
Number of pages15
Issue number6
Publication statusPublished - 2018 Jun 1


  • COA7
  • genetics
  • neuropathy
  • spinocerebellar ataxia
  • whole-exome sequencing

ASJC Scopus subject areas

  • Clinical Neurology


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