Essential tremor

Essential tremor is a disorder of the nervous system that causes involuntary, rhythmic shaking (tremor), especially in the hands. It involves tremor without any other signs or symptoms, and is distinguished from tremor that results from other disorders or known causes, such as tremors seen with Parkinson disease or head trauma.

Essential tremor usually occurs when the muscles are opposing gravity, such as when the hands are extended, and worsens with movement. This type of tremor is usually not evident at rest.

In addition to the hands and arms, muscles of the trunk, face, head and neck may also exhibit tremor in this disorder; the legs and feet are not usually involved. Head tremor may appear as a "yes-yes" or "no-no" movement while the affected individual is seated or standing. In some people with essential tremor, voice quality may be affected.

Essential tremor is not considered a dangerous or debilitating condition, and it does not shorten the lifespan. If severe, however, it may interfere somewhat with fine motor skills such as using eating utensils, writing, shaving, or applying makeup. Symptoms of essential tremor may be aggravated by emotional stress, fatigue, hunger, caffeine, cigarette smoking, or extremes of temperature.

Essential tremor may appear at any age, but is most common in the elderly. Some studies have suggested that people with essential tremor may have a higher than average risk of developing Parkinson disease, sensory problems such as hearing loss, or other neurological conditions, while others suggest that essential tremor may be associated with increased longevity.

Essential tremor is a common disorder, affecting millions of people in the United States. Estimates of its prevalence vary widely because several other disorders, as well as certain medications and other factors, can result in similar tremors. Essential tremor may affect as many as 14 percent of people over the age of 65.

Essential tremor is a complex disorder. Several genes are believed to help determine an individual's risk of developing this condition. Environmental factors may also be involved.

Some studies have found the DRD3 gene to be associated with essential tremor. The DRD3 gene provides instructions for making a protein called dopamine receptor D3, which is found in the brain. This protein responds to a chemical messenger (neurotransmitter) called dopamine to trigger signals within the nervous system, including signals involved in producing physical movement. A DRD3 variant seen in some families affected by essential tremor may cause the corresponding dopamine receptor D3 protein to respond more strongly to the neurotransmitter, possibly causing the involuntary shaking seen in this condition.

In other studies, the gene HS1BP3 has also been associated with essential tremor. The HS1BP3 gene provides instructions for making a protein called hematopoietic-specific protein 1 binding protein 3. This protein is believed to help regulate chemical signaling in the brain region involved in coordinating movements (the cerebellum) and in specialized nerve cells in the brain and spinal cord that control the muscles (motor neurons). An HS1BP3 variant has been identified in some families affected by essential tremor, but it has also been found in unaffected people. It is unknown what relationship, if any, this genetic change may have to the signs and symptoms of this condition.

Essential tremor can be passed through generations in families, but the inheritance pattern varies. In most affected families, essential tremor appears to be inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In other families, the inheritance pattern is unclear. Essential tremor may also appear in people with no previous history of the disorder in their family.