Essential tremor (ET) is a condition in which there is abnormal rhythmic involuntary movement, or tremor, of one or more parts of the body, especially the hands. It has no known pathology and its cause has not yet been identified. It is usually an isolated movement disorder, but may progress with age. Though it is the most frequently encountered movement disorder, there is a scarcity of research on ET.
Features of essential tremor
Affected subjects also have a higher risk of Parkinson disease, or of sensory loss in one or more areas. In addition, one or more family members of individuals with the condition may have it as well, or may have dystonic movement disorders. Gait, speech, or posture disturbances may coexist with it.
Essential tremor usually appears over the age of 40, and typically over 65 years. Both men and women have equal rates. Onset over the age of 65 is associated with a higher chance of developing neurological disorders such as Parkinson disease.
The cause of this condition is as yet unknown. Studies in twins have shown a high rate of genetic heritability, while other population studies have shown a very high rate of familial incidence. It is now thought that both genetic and environmental factors interact before the condition manifests.
Issues for which research is required include:
- Determining the pathophysiology of ET, and how it is responsible for the variation in clinical features. This will, in turn, help to devise effective therapies.
- The low incidence of true positive reporting makes population studies challenging in the absence of direct examination of the study subjects and their families.
- The determination of the genetic markers for this condition, based on the fact that there is an established familial component to it. An autosomal dominant inheritance is already a foregone conclusion in many cases of essential tremor.
- Again, some researchers are studying the possibility that epigenetic changes, rather than single gene changes, are responsible for ET. Epigenetics refers to the occurrence of mechanisms that alter a gene’s expression or its activity, without causing any structural change in the actual sequence of nucleotides - such as methylation. These changes are heritable, and may underlie ET, especially as they are not detectable by the usual genome sequencing techniques. New advanced procedures are being developed to deal with this possibility, such as methylome analysis.
- Another research avenue is the potential of essential tremor to be a complex trait. This requires high-throughput sequencing, which is a developing technology. Structure variants including variations in copy number is also a field which may contribute to a better understanding of ET.
A new area of exploration is based on the intriguing fact that a small amount of alcohol reduces the severity of ET. Thus other substances, namely, octanic acid and 1-octanol, are being studied for their effectiveness in the treatment of this condition. They produce a similar effect but do not result in intoxication.
Well-designed cost-benefit studies and clinical trials are required to find the best treatment options, especially comparing drug-based and surgical regimens.
Neuroprotective approaches are yet to be developed.
Reviewed by Afsaneh Khetrapal BSc (Hons)