There are several inherited disorders that have similar symptoms. These overlapping symptoms can make it difficult to distinguish between disorders. Essential tremor is often caused by a genetic mutation, which is a familial tremor. However, all cases of essential tremor are not inherited and the cause is unclear. The focus of this paper will be on familial essential tremor (Plumb and Bain, 2007). Essential tremor is often mistaken as Parkinson's disease, a well known genetic disease that affects the nervous system, due to their similar symptoms of tremors. Although essential tremor is not as well known as Parkinson's disease, it affects more humans than Parkinson's disease. Essential tremor is a common inherited involuntary movement disorder that is not related to Parkinson's disease (Essential tremor, 2010).
Essential tremor is characterized by an involuntary rhythmic tremor of the hands. Tremor may also occur in the arms, head and voice (Essential tremor, 2009).
The biological consequence of essential tremor is embarrassment, annoyance, and impedes consuming food and beverages (Essential Tremor, 2009).
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The pattern of inheritance of essential tremor is an autosomal dominant trait (Essential Tremor, 1998).
Only one abnormal gene from one parent is necessary to develop essential tremor. (Essential tremor, 2011). The offspring of a parent with essential tremor has a 50 percent chance of inheriting the disorder (Essential Tremor, 1998).
It is estimated that 1 percent of the population is affected with essential tremor (Plumb and Bain, 2007).
The screening process of essential tremor is a physical exam, family history and an elimination of other causes of tremor (Essential tremor, 2009).
The two main medications used to treat the tremors are Propranolol and Primidone. Other beta-blockers and anticonvulsive drugs are also used and surgery may be used in severe cases (Essential tremor, 2009).
Essential tremor is not life threatening but can interfere with everyday life tasks (Essential tremor, 2009).
Age of onset can be at any age, but usually happens in the teen years or at 45 years of age. Tremors normally worsen with age (Plumb and Bain, 2007).
Essential tremor (ET) and Parkinson's disease (PD) have several differences. Although both disorders are associated with tremors, there is a difference in the tremors. The tremors associated with PD occur when the hands are resting and disappear during movement. ET is the opposite, with involuntary shaking occurring during movement and disappearing with rest. ET can cause nodding of the head and voice tremors, unlike PD which normally does not (Essential tremor, 2010). PD changes walking patterns and posture causing loss of balance unlike ET which does not (Parkinson disease, 1998).
Research has shown that both of these disorders show changes in the brain. Dopamine is a chemical messenger that allows the body to move normally. There is a loss of brain cells that produce this chemical messenger in PD. The brains of ET show a loss of cells that produce GABA, which is a major inhibitory neurotransmitter in the brain (Essential tremor and how to manage it, 2010). Lewy bodies (abnormal protein) occur in both PD and ET, however in different areas of the brain (Brody, 2009).
In the Early stages of these disorders, they are sometimes misdiagnosed for one another. The misdiagnosis rate in PD is as high as 20% to 30%. And one of three ET patients is misdiagnosed. Transcranial sonography is now being used to distinguish between the two disorders. It has been discovered that an increase in echogenicity (reflect sound wave and produce echoes) in an area in the midbrain called the substantia nigra, is present in PD. Substantia nigra hyperechogenicity is not involved in ET. Transcranial sonography can detect hyperechogenicity allowing for a correct diagnosis and distinguish between ET and PD (Budisic, Trkanjec et al, 2009). Another way to distinguish between these two disorders is the effects of alcohol on the tremors. A small amount of alcohol will decrease the tremors in ET but has no effect on PD tremors (Plumb and Bain, 2007).
Both ET and PD are inherited disorders but different genes are related to each disorder. ET is inherited in an autosomal dominant pattern (Essential Tremor, 1998). PD can be inherited in an autosomal dominant pattern or an autosomal recessive pattern, depending on the genes that are mutated (Parkinson Disease, 2011). A mutation of gene ETM1, also known as FET1, mapped to chromosome 3 and gene ETM2 mapped to chromosome 2 is the cause of ET (Essential Tremor, 1998). Mutations in the LRRK2 or SNCA gene cause PD to be inherited in an autosomal dominant pattern. PARK2, PARK7, or PINK1 gene being mutated causes PD to be inherited in an autosomal recessive pattern (Parkinson Disease, 2011). These genes are mapped to chromosome 4 (Parkinson disease, 1998).
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Due to the ongoing controversy as to whether ET and PD are related, studies have been performed. One study evaluated families with ET and found that PD was not dominant in their family history. These findings support the fact that ER and PD are two separate inherited disorders (Marttila, Rautakorpi et al, 1984).
Essential tremor and Parkinson's disease can be easily mistaken for one another, but looking a little deeper one can see that they are individual disorders. Symptoms resemble each other but have their differences. Both diseases are inherited but the mutated genes affected are different in both disorders. Essential tremor is an inherited movement disorder that is more common than Parkinson's disease, but they are not related (Plumb and Bain, 2007).
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