Diann Shaddox Foundation for Essential Tremor
What Causes Essential Tremor?
The true cause of essential tremor is still not understood, but it is thought that the abnormal electrical brain activity that causes tremor is processed through the thalamus. The thalamus is a structure deep in the brain that coordinates and controls muscle activity.
Genetics is responsible for causing ET in half of all people with the condition. A child born to a parent with ET will have up to a 50% chance of inheriting the responsible gene, but may never actually experience symptoms. Although ET is more common in the elderly -- and symptoms become more pronounced with age -- it is not a part of the natural aging process.
Essential tremor is known to be familial condition, meaning that it runs in families. At least 5-7 out of 10 people with essential tremor have other members of the family with the same condition. Genes are passed on to a child from each parent and determine what we look like, how our body functions and even what diseases we get. Particular genes have been shown to have certain changes present in families with essential tremor.
It is not clearly understood how this genetic change leads to essential tremor. However, it is likely that it somehow affects some parts of the brain that are responsible for controlling movement.
What is tremor?
Tremor is an unintentional, rhythmic muscle movement involving to-and-fro movements (oscillations) of one or more parts of the body. It is the most common of all involuntary movements and can affect the hands, arms, head, face, voice, trunk, and legs. Most tremors occur in the hands. In some people, tremor is a symptom of a neurological disorder or appears as a side effect of certain drugs. The most common form of tremor, however, occurs in otherwise largely healthy people. Although tremor is not life-threatening, it can be embarrassing to some people and make it harder to perform daily tasks.
What are the characteristics of tremor? Characteristics may include a rhythmic shaking in the hands, arms, head, legs, or trunk; shaky voice; difficulty writing or drawing; or problems holding and controlling utensils, such as a fork. Some tremors may be triggered by or become exaggerated during times of stress or strong emotion, when the individual is physically exhausted, or during certain postures or movements.
Tremor may occur at any age but is most common in middle-aged and older persons. It may be occasional, temporary, or occur intermittently. Tremor affects men and women equally.
A useful way to understand and describe tremors is to define them according to the following types. Resting tremoroccurs when the muscle is relaxed, such as when the hands are lying on the lap or hanging next to the trunk while standing or walking. It may be seen as a shaking of the limb, even when the person is at rest. Often, the tremor affects only the hand or fingers. This type of tremor is often seen in patients with Parkinson’s disease. An action tremor occurs during any type of movement of an affected body part. There are several subclassifications of action tremor. Postural tremor occurs when the person maintains a position against gravity, such as holding the arms outstretched. Kinetictremor appears during movement of a body part, such as moving the wrists up and down, while intention tremor is present during a purposeful movement toward a target, such as touching a finger to one’s nose during a medical exam. Task-specific tremor appears when performing highly skilled, goal-oriented tasks such as handwriting or speaking. Isometric tremor occurs during a voluntary muscle contraction that is not accompanied by any movement.
How common is essential tremor?
Essential tremor is a common disorder, affecting up to 10 million people in the United States. Estimates of its prevalence vary widely because several other disorders, as well as other factors such as certain medications, can result in similar tremors. In addition, mild cases are often not brought to medical attention, or may not be detected in clinical exams that do not include the particular circumstances in which an individual's tremor occurs. Severe cases are often misdiagnosed as Parkinson disease.
What genes are related to essential tremor?The causes of essential tremor are unknown. Researchers are studying several areas (loci) on particular chromosomes that may be linked to essential tremor, but no specific genetic associations have been confirmed. Several genes as well as environmental factors likely help determine an individual's risk of developing this complex condition. The specific changes in the nervous system that account for the signs and symptoms of essential tremor are unknown.
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