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FB2026_01
,
released March 12, 2026
This report describes spinocerebellar ataxia, autosomal recessive, with axonal neuropathy 3 (SCAN3). In the course of genomic analyses, including whole exome sequencing (WES), of a cohort of patients with neurologic features typically observed in mitochondrial diseases (including ataxia, spasticity and neuropathy), variants in the cytochrome c oxidase assembly factor 7 (COA7) gene were identified in four unrelated patients. The COA7 gene encodes a protein that localizes to the mitochondria and is involved in the assembly of mitochondrial complex IV and possibly mitochondrial complex I. There is a single orthologous gene in Drosophila, Dmel\Coa7, for which RNAi targeting constructs have been generated.
The human COA7 gene has not been introduced into flies.
Pan-neuronal knockdown of Dmel\Coa7, effected by RNAi, results in reduced adult lifespan, progressive impairment in locomotive ability in adults, and shortened synaptic branches of motor neurons in larval neuromuscular junctions.
[updated Apr. 2019 by FlyBase; FBrf0222196]
Spinocerebellar ataxia with axonal neuropathy is an autosomal recessive neuromuscular disorder typically characterized by onset in the first or second decade of gait disturbance, slowly progressive distal muscle weakness, and axonal sensorimotor neuropathy with distal sensory impairment. [from MIM:218387, MIM:607250; 2020.07.14]
[SPINOCEREBELLAR ATAXIA, AUTOSOMAL RECESSIVE, WITH AXONAL NEUROPATHY 3; SCAN3](https://omim.org/entry/618387)
[CYTOCHROME C OXIDASE ASSEMBLY FACTOR 7; COA7](https://omim.org/entry/615623)
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 (Higuchi et al., 2018; pubmed:29718187; FBrf0238967).
Recessive inheritance was exhibited (Higuchi et al., 2018; pubmed:29718187; FBrf0238967).
Autosomal recessive spinocerebellar ataxia with axonal neuropathy-3 (SCAN3) is caused by homozygous or compound heterozygous mutation in the COA7 gene. [from MIM:618387; 2019.04.24]
Nerve conduction studies showed axonal sensorimotor neuropathy. Sural nerve biopsies showed chronic axonal degeneration with a marked loss of large and medium myelinated fibers (Higuchi et al., 2018; pubmed:29718187; FBrf0238967).
Cytochrome c oxidase assembly factor 7 (COA7) is required for assembly of mitochondrial respiratory chain complex I and complex IV. [Gene Cards, COA7; 2018.09.14]
The COA7 gene encodes a protein that localizes to the mitochondria and is involved in the assembly of mitochondrial complex IV, which is the terminal component of the mitochondrial respiratory chain (summary by Martinez Lyons et al., 2016; pubmed:27683825). [from MIM:615623; 2018.09.14]
One to one: 1 human to 1 Drosophila.
High-scoring ortholog of human COA7 (1 Drosophila to 1 human). Dmel\Coa7 shares 32% identity and 50% similarity with the human gene.