CCG•CGG interruptions in high-penetrance SCA8 families increase RAN translation and protein toxicity.

EMBO molecular medicine 2021 Nov 08

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Spinocerebellar ataxia type 8 (SCA8), a dominantly inherited neurodegenerative disorder caused by a CTG•CAG expansion, is unusual because most individuals that carry the mutation do not develop ataxia. To understand the variable penetrance of SCA8, we studied the molecular differences between highly penetrant families and more common sporadic cases (82%) using a large cohort of SCA8 families (n = 77). We show that repeat expansion mutations from individuals with multiple affected family members have CCG•CGG interruptions at a higher frequency than sporadic SCA8 cases and that the number of CCG•CGG interruptions correlates with age at onset. At the molecular level, CCG•CGG interruptions increase RNA hairpin stability, and in cell culture experiments, increase p-eIF2α and polyAla and polySer RAN protein levels. Additionally, CCG•CGG interruptions, which encode arginine interruptions in the polyGln frame, increase toxicity of the resulting proteins. In summary, SCA8 CCG•CGG interruptions increase polyAla and polySer RAN protein levels, polyGln protein toxicity, and disease penetrance and provide novel insight into the molecular differences between SCA8 families with high vs. low disease penetrance. © 2021 The Authors. Published under the terms of the CC BY 4.0 license.

Citation

Barbara A Perez, Hannah K Shorrock, Monica Banez-Coronel, Tao Zu, Lisa El Romano, Lauren A Laboissonniere, Tammy Reid, Yoshio Ikeda, Kaalak Reddy, Christopher M Gomez, Thomas Bird, Tetsuo Ashizawa, Lawrence J Schut, Alfredo Brusco, J Andrew Berglund, Lis F Hasholt, Jorgen E Nielsen, S H Subramony, Laura Pw Ranum. CCG•CGG interruptions in high-penetrance SCA8 families increase RAN translation and protein toxicity. EMBO molecular medicine. 2021 Nov 08;13(11):e14095