HD is known to attack the basal ganglia, a deep-brain cluster of nerve cells at the base of the cerebrum. Huntington's disease, also known as Huntington's chorea, is an inherited condition caused by a genetic mutation in the Huntington gene that causes certain nerve cells in the cerebrum to deteriorate and die. It is a progressive degenerative disease marked by involuntary, jerky movements in the arms, neck, trunk and face. Other symptoms include a wide, prancing gait, hesitant speech and intellectual deterioration. Symptoms appear in the fourth or fifth decade of life, and then progress steadily during the succeeding 10 to 20 years.
Death follows, and there are no effective treatments available.
A second, similar study included six control subjects with cerebellar injuries. Researchers asked the subjects to reach quickly for targets while grasping a robotic arm. Results were then analyzed by a computer. While initial aiming was not dramatically disturbed in HD patients, all HD patients and several of the asymptomatic HD gene-carrier patients made movements with unusual jerkiness as the movement progressed. These results suggest, Smith says, that HD movements often begin normally, but become jerky and irregular at some point during their course because of impaired error feedback.