Saccadometry of conditional rules in presymptomatic Huntington's disease.

The promise of new treatments for Huntington's disease (HD) has intensified interest in markers of preclinical onset and progression. Recent research has shown that elementary saccadic tasks may exhibit subtle preclinical abnormalities. Other studies have shown cognitive dysfunction to be a major component of early-HD phenotype. It was hypothesized that the synergistic combination of an oculomotor response with a cognitively demanding paradigm might therefore offer a functional marker that could be superior both to simpler saccadic paradigms and to conventional cognitive tests. The performance of 12 early-symptomatic HD patients and 17 presymptomatic gene carriers on three saccadic paradigms were studied: prosaccades, color-cued centrally triggered saccades and a second-order conditional rule task on which the direction of the saccade was cued by the combination of central and peripheral cues. Eye movements were recorded using a highly portable, patient-friendly infrared recording device. The analysis of the latency distributions showed that the second-order conditional rule task could discriminate between clinical groups, had a predictive potential within the presymptomatic group and appeared to be more sensitive than easier tasks. The simplicity of portable saccadometry, combined with the sensitivity of a complex oculomotor task, may therefore offer a promising functional marker in HD.