Genetic and Clinical Investigations of C12orf65 Gene Mutations in Three Chinese Pedigrees.

Background: C12orf65 (chromosome 12 open reading frame 65) gene encodes a mitochondrial matrix protein essential for the release of newly synthesized proteins from mitochondrial ribosomes. Biallelic pathogenic variants result in loss of function in the protein complex necessary for oxidative phosphorylation. Pathogenic C12orf65 variants have been associated with various inherited neurological diseases, including Behr syndrome, Leigh syndrome, combined oxidative phosphorylation deficiency 7, and hereditary spastic paraplegia.

Methods: This was a retrospective case series of 4 children with C12orf65 mutation from 3 unrelated pedigrees of Chinese descent. Clinical and diagnostic data were collected via retrospective medical record review. The phenotypic manifestations were systematically documented, and the genotypic data were analyzed in conjunction with previous reports.

Results: Four subjects exhibited optic nerve atrophy, strabismus, progressive lower limb dystonia, and abnormal gait. Whole exome sequencing revealed the c.394C>T variant in C12orf65 in all 4 patients. Three of the patients had coexisting novel MT-ND4 (m.11696 G>A) and OPA1 (c.1817G>A) variants.

Conclusions: We analyzed the gene-phenotypic associations of 4 patients in conjunction with previous reports which added to the current understanding of C12orf65-related neurodegenerative disorders. The superimposed mutations in 2 of these patients suggest that the heterogeneity of optic neuropathy and the systemic features associated with C12orf65 pathogenic variants may be altered by the genetic background of mitochondrial or nuclear genes that influence mitochondrial function. We recommend genetic evaluation of C12ORF65-related diseases, including other genes responsible for optic neuropathy, and not just limited to Sanger sequencing.