Saccades velocity is strongly influenced by polyglutamine size in spinocerebellar ataxia type 2

Background: Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominant inherited disorder which is clinically characterized by progressive cerebellar ataxia, dysarthria, neuropathy and early slowing of horizontal saccadic eye movements. The underlying mutation is an unstable expansion of a polyglutamine domain within the protein ataxin-2. The prevalence of SCA2 is particulary high in Holguín province, Cuba. Methods: We measured the horizontal saccade velocity of 82 Cuban SCA2 patients with genetically tested polyglutamine repeat size ranging from 34 to 50 (mean 40, SD 3) and disease duration from 1 to 42 years (mean 13.3, SD 7.9). The clinical assessment (ataxia score) was carried out using the International Cooperative Ataxia Rating Scale. 80 healthy non-paid volunteers served as control group. Horizontal saccades with amplitudes of 10°, 20°, 30° and 60° were recorded binocularly with silver-silver electrodes and a 2-channel Otoscreen AC electronystagmograph (Jaeger-Toennies, Höchberg, Germany) and analysed by MATLAB software and statistical tests. Results: Maximum saccadic velocity (MSV) showed significant differences at 10°, 20°, 30° and 60° (p