Somatic instability of the FGF14-SCA27B GAA•TTC repeat reveals a marked expansion bias in the cerebellum.

TitleSomatic instability of the FGF14-SCA27B GAA•TTC repeat reveals a marked expansion bias in the cerebellum.
Publication TypeJournal Article
Year of Publication2024
AuthorsPellerin D, Méreaux J-L, Boluda S, Danzi MC, Dicaire M-J, Davoine C-S, Genis D, Spurdens G, Ashton C, Hammond JM, Gerhart BJ, Chelban V, Le PU, Safisamghabadi M, Yanick C, Lee H, Nageshwaran SK, Matos-Rodrigues G, Jaunmuktane Z, Petrecca K, Akbarian S, Nussenzweig A, Usdin K, Renaud M, Bonnet C, Ravenscroft G, Saporta MA, Napierala JS, Houlden H, Deveson IW, Napierala M, Brice A, Porcel LMolina, Seilhean D, Züchner S, Durr A, Brais B
JournalBrain
Date Published2024 Oct 08
ISSN1460-2156
Abstract

Spinocerebellar ataxia 27B (SCA27B) is a common autosomal dominant ataxia caused by an intronic GAA•TTC repeat expansion in FGF14. Neuropathological studies have shown that neuronal loss is largely restricted to the cerebellum. Although the repeat locus is highly unstable during intergenerational transmission, it remains unknown whether it exhibits cerebral mosaicism and progressive instability throughout life. We conducted an analysis of the FGF14 GAA•TTC repeat somatic instability across 156 serial blood samples from 69 individuals, fibroblasts, induced pluripotent stem cells, and post-mortem brain tissues from six controls and six patients with SCA27B, alongside methylation profiling using targeted long-read sequencing. Peripheral tissues exhibited minimal somatic instability, which did not significantly change over periods of more than 20 years. In post-mortem brains, the GAA•TTC repeat was remarkably stable across all regions, except in the cerebellar hemispheres and vermis. The levels of somatic expansion in the cerebellar hemispheres and vermis were, on average, 3.15 and 2.72 times greater relative to other examined brain regions, respectively. Additionally, levels of somatic expansion in the brain increased with repeat length and tissue expression of FGF14. We found no significant difference in methylation of wild-type and expanded FGF14 alleles in post-mortem cerebellar hemispheres between patients and controls. In conclusion, our study revealed that the FGF14 GAA•TTC repeat exhibits a cerebellar-specific expansion bias, which may explain the pure cerebellar involvement in SCA27B.

DOI10.1093/brain/awae312
Alternate JournalBrain
PubMed ID39378335
Grant ListR01 NS081366 / NS / NINDS NIH HHS / United States