Objective:

Not applicable

Background:

Spinocerebellar ataxia type 27B (SCA27B) due to GAA trinucleotide repeats in the fibroblast growth factor 14 (FGF14) gene, newly discovered in 2022, is emerging as a common cause of late-onset ataxia, as well as neuro-ophthalmologic presentations. We aim to familiarize the neurologist with this new diagnosis and to delineate the causes of diplopia, which have not yet been described.

Design/Methods:

Not applicable

Results:

Retrospective analysis of 12 patients [mean age at symptom onset 64 (range 44-73) years] with genetically confirmed SCA27B. Seven patients had episodic or persistent oscillopsia or diplopia at symptom onset, neurologically isolated for several years in 3. Eight of 11 treated patients experienced improvement in oscillopsia and/or imbalance on 4-aminopyridine. All patients had downbeat nystagmus detectable on exam, though it was clinically obvious in only 3. Diplopia was present in 9 patients: vertical due to skew deviation (static or alternating on lateral gaze) (n=6) and/or horizontal due to vergence dysfunction (n=8), including convergence insufficiency (n=4) and divergence insufficiency with cerebellar esotropia (n=3). One patient had saccadic slowing, confirmed with oculography.

Conclusions:

SCA27B is a newly discovered diagnosis that is evolving as a common cause of late-onset episodic or slowly progressive ataxia and idiopathic downbeat nystagmus. Patients often present with oscillopsia or diplopia, including unique features such as hours-long discrete episodes, and exam features can be subtle; thus, it is important that neurologists become familiar with this condition and its neuro-ophthalmic manifestations, particularly given its uniquely responsivity to 4-aminopyridine.