Background: Spinocerebellar ataxia type 27B (SCA27B), caused by a GAA repeat expansion in FGF14, is a recently described genetic etiology of idiopathic late-onset cerebellar ataxia (ILOCA). Downbeat nystagmus (DBN) is increasingly recognized as a clinical hallmark of this condition. We aimed to assess the diagnostic value of video-oculography (VOG) in detecting SCA27B and its role in monitoring response to 4-aminopyridine (4-AP) in a real-world clinical setting.
Methods: We retrospectively analyzed patients with ILOCA referred to Fondation Rothschild Hospital (Paris, France) from February 2023 to January 2024. All underwent clinical, MRI, and VOG assessments, with genetic testing for FGF14-GAA expansions. Clinical and oculomotor features of carriers (≥ 200 repeats) and non-carriers were compared. A subset of symptomatic carriers received 4-AP and were evaluated at baseline, 2 months, and 8 months using the Scale for the Assessment and Rating of Ataxia (SARA) and VOG.
Results: Twelve of 34 tested patients (35%) were FGF14-GAA expansion carriers. DBN was significantly more frequent in carriers than in non-carriers (92% vs. 33%, p = 0.003), often associated with gaze-evoked nystagmus (75% vs. 19%, p = 0.005). MRI did not distinguish carriers from non-carriers. Of the nine patients treated, all reported enhanced balance, which is corroborated by the improvement in the SARA score from a median of 5.5-3 at 2 months (p = 0.015), with sustained benefit at 8 months.
Conclusions: VOG is a key diagnostic tool for detecting DBN, which is strongly associated with SCA27B, facilitating targeted genetic testing. 4-AP is an effective symptomatic treatment.
Keywords: SCA27B; cerebellar ataxia; downbeat nystagmus; movement disorders; neurogenetics; video‐oculography.
© 2025 The Author(s). European Journal of Neurology published by John Wiley & Sons Ltd on behalf of European Academy of Neurology.