Hereditary degenerative disorder of the nervous system, associated with dementia and uncontrollable dance-like movements. The disease affects adults, and is a dominant hereditary disorder, that is, on average half the children of the affected person will suffer from it. The disordered movement and dementia may occur at the same time, or one after the other. The movements are involuntary and abrupt, and accompanied by grimaces and twisting movements of trunk and shoulders; sometimes the limbs are thrown out, hence the dance-like walking pattern. After a few years the chorea is so dominant that normal daily activity and possibly speech as well can be affectea. Emotion worsens the involuntary movements. Dementia is often preceded by character changes and disturbed behaviour, and the condition is sometimes associated with psychiatric disorders such as delusions. The speed at which the patient deteriorates varies, but the pattern is often the same within a particular family. Finally the patient is reduced to complete helplessness by dementia and disability. There is no treatment; certain medicines can reduce the severity of the symptoms, but cannot influence the course of the disease.