<i>C9ORF72</i> expansion is not a significant cause of sporadic spinocerebellar ataxia

Hexanucleotide expansions within the first intron of the C9ORF72 gene are a significant cause of familial frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS), alone or in combination, as well as sporadic ALS worldwide.1-3 Several recent reports have described cases that broaden the clinical phenotype to include behavioral-variant FTD with or without early psychiatric presentations and parkinsonian features4, 5 and primary progressive aphasia.6 There is also a report of a patient with a family history of ALS and cerebellar ataxia,5 an intriguing finding as neuroimaging of C9ORF72 patients shows cerebellar atrophy, which is not typically observed with other FTD-related mutations such as MAPT or GRN.7 Cerebellar neuronal cytoplasmic inclusions have also been observed in multiple studies,6, 7 yet clinical cerebellar ataxia has not been detected in any large cohorts of C9ORF72 patients with FTD and/or ALS.1-3, 7 Because a majority of adult-onset ataxia cases are of unknown etiology, these observations raise the possibility that C9ORF72 may contribute to the development of sporadic spinocerebellar ataxia. To address this question, we examined 209 adult-onset sporadic ataxia patients for C9ORF7 hexanucleotide expansion (Table 1). All patients were screened for common genetic spinocerebellar ataxias including SCA1, SCA2, SCA3, SCA6, SCA7, and/or Friedreich ataxia. Most patients (40%) had pure cerebellar ataxia, but given the known C9ORF72 phenotypes, cases associated with upper motor neuron signs, dementia, and parkinsonism were also included. Approximately one third of these patients met possible or probable criteria for multiple system atrophy. Testing was performed as previously described,3 and only 1 positive case was identified (1 of 209, 0.5%). This patient, currently age 53, developed slowly progressive cerebellar dysfunction in her early 20s with falls by age 25. Upper motor neuron features of increased lower extremity tone and hyperreflexia were present, but annual assessments have shown no lower motor neuron involvement or cognitive decline. MRI has shown cerebellar atrophy with no frontal or temporal involvement. Evaluation for other genetic causes involving the APTX, ATN1, ATXN1, ATXN2, ATXN3, ATXN7, ATXN8, ATXN10, CACNA1A, FMR1, FXN, KCNC3, PRKCG, PP2R2B, SACS, SETX, SPTBN2, and TBP genes was unremarkable. She is white with French-Canadian ancestry. As with the prior reported C9ORF72 ataxia case,5 family history was notable for her father and paternal uncle being diagnosed with ALS and dying within 2 years of symptom onset. There were no other affected family members. We speculate that the clinical findings seen in our patient represent a rare (<1%) C9ORF72 phenotype5; however, given the lack of other affected family members or unrelated cases, we cannot confirm this. C9ORF72 penetrance varies by age, with full penetrance occurring by the ninth decade,1 and it is possible that our patient will still develop a more classic phenotype. Regardless, this study does not support genetic testing for C9ORF72 expansion in sporadic spinocerebellar ataxia, although, as our study only examined sporadic-onset cases, it remains possible that C9ORF72 may contribute more significantly to dominant familial forms. For now, C9ORF72 testing would only be indicated for ataxia patients with a family history of ALS and/or FTD. We thank all the patients and their families who contributed to this project. Brent L. Fogel and Giovanni Coppola were responsible for the conception and design of the research project. Mochtar Pribadi and Sarah Pi were responsible for project execution. Susan L. Perlman and Daniel H. Geschwind supervised the clinical phenotyping and the molecular aspects of the project, respectively. Brent L. Fogel wrote the manuscript, and Brent L. Fogel, Giovanni Coppola, Susan L. Perlman, and Daniel H. Geschwind were responsible for its review and critique. Financial Disclosures: Mochtar Pribadi and Sarah Pi have nothing to disclose. Brent L. Fogel has received funding from the National Institutes of Health (NIH) and the National Ataxia Foundation. Susan L. Perlman has received support from Santhera Pharmaceuticals to conduct a phase 3 idebenone study. Daniel H. Geschwind has received royalty payments from Yale University and Chemicon for antibody sales and funding from the NIH and private foundations. Giovanni Coppola has received funding from the NIH, the Muscular Dystrophy Association, and private foundations. Brent L. Fogel MD, PhD*, Mochtar Pribadi PhD*, Sarah Pi*, Susan L. Perlman MD*, Daniel H. Geschwind MD, PhD* , Giovanni Coppola MD* , * Program in Neurogenetics, Department of Neurology David Geffen School of Medicine, University of California Los Angeles Los Angeles, California, USA, Department of Psychiatry, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA, Department of Human Genetics, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA.

Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.