Video-Oculography as a Key Diagnostic Tool for SCA27B: A Real-Life Experience.

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.