Eye-tracking-aided characterization of saccades and antisaccades in SYNE1 ataxia patients: a pilot study

SYNE1 ataxia is an autosomal recessive hereditary condition, the main characteristic features of which are gait and limb ataxia and cerebellar dysarthria. Reports have revealed that the clinical phenotype of SYNE1 ataxia is more complex than the first published cases with pure cerebellar signs indicated. The aim of this study was to characterize eye movement alterations in the first diagnosed Hungarian SYNE1 ataxia patients.

Saccades and antisaccades were examined with an eye tracker device in 3 SYNE1 (one patient has two frameshift mutations [c.8515_8516insA, p.Met2839Asnfs*53 and c.11594_11595insG, p.Glu3866*] in a compound heterozygous state, whereas two subjects have a splicing variant [c.23146-2A > G] in a homozygous state), 6 Friedreich ataxia (FA) patients and 12 healthy controls. Besides that, detailed clinical phenotyping and comprehensive neuropsychological assessment were carried out in all patients with ataxia. In addition to the characteristic cerebellar alterations, pyramidal signs and polyneuropathy were observed at least in 2 SYNE1 ataxia patients, for which no other underlying reason was found. The eye tracking assessment revealed hypometric saccades in the longer amplitude (18.4°) saccadic paradigm in all SYNE1 patients, whereas 2 out of 3 SYNE1 subjects performed slow saccades as well. In the antisaccade task, higher incorrect ratios of antisaccades were demonstrated in SYNE1 patients compared to healthy controls, showing inverse correlation with working memory test results. The corresponding data of FA patients was dispersed over a wide range, partially overlapping with control data.

The current study draws attention to the presence of eye movement disorders in patients with SYNE1 ataxia and demonstrates that alterations in the antisaccade paradigm may be related to working memory deficits.