Huntington's disease is a disease characterized by minor coordination problems, jerking eye movements, and uncontrollable movement of peripheral limbs. Symptoms generally occur at the age of 40, and are often accompanied by depression and psychosis. The disease is caused by a mutation in the Huntingtin gene, on chromosome 4, which causes abnormally large numbers of glutamate residues in the protein. Via an unknown mechanism, this accumulation leads to neurodegeneration in the caudate nucleus and putamen, selectively destroying GABAergic neurons which project to the globus pallidus. There is also significant necrosis in the thalamus and cerebral cortex. Cholinergic interneurons and dopaminergic neurons in the midbrain are largely unaffected. 
Treatment for Huntington's disease is extremely limited due to the lack of knowledge concerning the pathogenesis of protein accumulation, though drugs used include dopamine receptor antagonists to minimize tremors and antidepressants to ameliorate symptoms of psychosis and depression.