Walsh & Hoyt: Huntington's Disease

Huntingtons disease produces disturbances of voluntary gaze, particularly saccades. It is caused by a genetic defect of the IT15 gene (the ""Huntington"" gene) on chromosome 4, producing a CAG triplet repeat. Initiation of saccades in patients with Huntingtons disease may be difficult. Such patients show prolonged latencies, especially when the saccade is to be made on command, in anticipation of a target moving in a predictable fashion, or in a self-paced fashion. An obligatory blink or head turn may be used to start the eye moving. Saccades may be slow in the horizontal or vertical plane; this deficit can often be detected early in the disease if eye movements are measured, but it may not be evident clinically until late in the course. Saccades may be slower in patients who become symptomatic at an earlier age, and such persons are more likely to have inherited the disease from their father. The slowing of vertical saccades in Huntingtons disease probably does not occur in patients with chorea from nondegenerative conditions or tardive dyskinesia. Longitudinal studies of saccades can be used to quantify the progression of the disease.