Oculomotor deficits indicate the progression of Huntington's disease.

The oculomotor deficits associated with Huntington's Disease (HD) are one of the earliest signs of disease onset. They include a marked delay in executing voluntary saccades and a difficulty inhibiting saccades to task-irrelevant stimuli. In addition, HD patients develop a deficit in task-switching, which can be demonstrated by the continued adherence to a rule after it has been recently changed. These deficits are likely to be the result of a progressive neural degeneration of the fronto-striatal system, which is a distinguishing feature of HD neuropathology. It is predicted that as the disease progresses the magnitude of these specific deficits should increase. We tested a cohort of early HD patients and presymptomatic HD gene carriers on a series of oculomotor tasks designed to measure saccade initiation, inhibition and rule switch cost. Saccadic latencies and error rates in early HD patients were found to be systematically higher than controls. Presymptomatic HD subjects showed small increases in saccadic latencies and error rates that were in proportion to the predicted age of disease onset. These results suggest that saccadometry and a cognitively demanding oculomotor task may be useful as an indicator of function in HD.