Background: We observed a 90-member family with a rare combination of multiple neurodegenerative-disease phenotypes and performed a genetic study to identify the causative gene. Methods: We performed physical and neurological examinations with International Rating Scales to assess signs of ataxia, parkinsonism, and cognitive function, as well as brain magnetic resonance imaging (MRI) scans with seven sequences. We performed whole-genome sequencing on four affected and three unaffected members to identify the genetic cause of the phenotypes in the affected members. We searched for co-segregations of abnormal repeat-expansion loci, pathogenic mutations in known SCA-related genes, and novel rare mutations. Subsequently, a novel co-segregating missense mutation in CARS gene was validated by Sanger sequencing in an additional five affected and four unaffected members. Additionally, we generated Cars+/- knockout mice using CRISPR/Cas9 technology to investigate the functional role of the CARS gene. Findings: We found a novel late-onset parkinsonism/spinocerebellar-ataxia complex in this pedigree, which presented core characteristics (i.e., cerebellar ataxia, parkinsonism, and pyramidal signs) in all nine affected members and non-core neurodegenerative characteristics that differed across different posterity's families. Brain MRI showed cerebellar/pons atrophy, pontine-midline linear hyperintensity, decreased rCBF in the bilateral basal ganglia and cerebellar dentate nucleus, and hypointensities of the cerebellar dentate nuclei, basal ganglia, mesencephalic red nuclei, and substantia nigra, all of which suggested neurodegeneration with iron accumulation. We identified a heterozygous mutation in CARS (E795V) that significantly co-segregated in the pedigree. Remarkably, balance-related deficits and gait disturbances were observed in Cars+/− mice. In addition, pathological findings further revealed that CARS knockout induced dopaminergic neuronal loss in the substantia nigra and reduced parkin levels in the cerebellum. Interpretation: All family members carrying the CARS mutation had the same clinical manifestations of parkinsonism and spinocerebellar-ataxia, which corresponded to neuropathologic changes revealed via brain MRI that were replicated in transgenic animals with similar behavioral changes and pathological manifestations. Funding: This study was funded by the following: NIH-NIA Research Project; The National Key RD The Natural Science Foundation of China; CAMS Innovation Fund for Medical Sciences; Shenzhen Municipal of Government of China; The Strategic Priority Research Program of the Chinese Academy of Science. Declaration of Interest: The authors declare no competing interests. Ethical Approval: The animal experiments were approved by the Ethical Committee of the University of Science and Technology of China (USTC). The genetic data sharing was approved (2020BAT0031) by the Human Genetic Resources Administration of China (HGRAC).
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Jan 13, 2021
Song Shen + 5
Open Access
