HD is a classic neurodegenerative disease with dominant inheritance. It manifests as prominent degeneration of the striatum (caudate and putamen) in addition to involvement of the cortex, brainstem and cerebellum. The genetic basis of HD is a tri-nucleotide repeat (CAG) in the huntington protein. The number of triplet repeats influences the age of onset (the more repeats, the earlier age of onset) and the severity of the disorder. Patients with HD develop movement disorders (most often chorea early in the course), dementia and psychiatric disorders (most often mood disorders).