Tremor is an unintentional (involuntary), rhythmical alternating movement that may affect the muscles of any part of the body. Tremor is caused by the rapid alternating contraction and relaxation of muscles and is a common symptom of diseases of the nervous system (neurologic disease). Occasional tremor is felt by almost everyone, usually as a result of fear or excitement. However, uncontrollable tremor or shaking is a common symptom of disorders that destroy nerve tissue such as Parkinson's disease or multiple sclerosis. Tremor may also occur after stroke or head injury. Other tremor appears without any underlying illness.

The cause of essential tremor not linked to any other problem, is not known, although it is an inherited problem in more than half of all cases. The genetic condition has an autosomal dominant inheritance pattern, which means that any children of an affected parent will have a 50% chance of developing...