Comparison of vertical and horizontal saccade measures and their relation to gray matter changes in premanifest and manifest Huntington disease.

Saccades are a potentially important biomarker of Huntington disease (HD) progression, as saccadic abnormalities can be detected both cross-sectionally and longitudinally. Although vertical saccadic impairment was reported decades ago, recent studies have focused on horizontal saccades. This study investigated antisaccade (AS) and memory guided saccade (MG) impairment in both the horizontal and vertical directions in individuals with the disease-causing CAG expansion (CAG+; n = 74), using those without the expansion (CAG-; n = 47) as controls. Percentage of errors, latency, and variability of latency were used to measure saccadic performance. We evaluated the benefits of measuring saccades in both directions by comparing effect sizes of horizontal and vertical measures, and by investigating the correlation of saccadic measures with underlying gray matter loss. Consistent with previous studies, AS and MG impairments were detected prior to the onset of manifest disease. Furthermore, the largest effect sizes were found for vertical saccades. A subset of participants (12 CAG-, 12 premanifest CAG+, 7 manifest HD) underwent magnetic resonance imaging, and an automated parcellation and segmentation procedure was used to extract thickness and volume measures in saccade-generating and inhibiting regions. These measures were then tested for associations with saccadic impairment. Latency of vertical AS was significantly associated with atrophy in the left superior frontal gyrus, left inferior parietal lobule, and bilateral caudate nuclei. This study suggests an important role for measuring vertical saccades. Vertical saccades may possess more statistical power than horizontal saccades, and the latency of vertical AS is associated with gray matter loss in both cortical and subcortical regions important in saccade function.