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SLC1A2 variant associated with essential tremor but not Parkinson disease in Chinese subjects.

From the Departments of Neurology (E.-K.T.) and Clinical Research (E.-K.T., Y.Z.), Singapore General Hospital
Neurology (Impact Factor: 8.3). 04/2013; 80(17). DOI: 10.1212/WNL.0b013e31828f1903
Source: PubMed
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    ABSTRACT: Essential tremor (ET) is a prevalent neurological disorder of unknown etiology characterized by the presence of an action tremor that occurs during voluntary motion and affects primarily the upper limbs. The worldwide prevalence of the disease in the general population is 0.9%, increasing to 4.6% in individuals ≥ 65 years old. Standard pharmaceutical treatments are only moderately effective, reducing tremor amplitudes in ∼ 50% of patients, a phenomenon partly explained by the fact that the diagnosis of ET is based solely on clinical findings rather than biological markers. Furthermore, the pathophysiological origin of ET remains controversial, leading to heated debates as to whether it should be considered a neurodegenerative disorder or as a dynamic oscillatory disturbances of neurologic origin. Progress has been made in the understanding of its etiology as it is now accepted that genetic components must at least explain the familial cases of ET, and the evidence implicating the olivocerebellar and cerebello-thalamo-cortical pathways is strong. However, a strong disconnection between human genetics, pathophysiological, and mouse genetics studies exists in the field of ET, with little use of all the knowledge gathered from the different research disciplines. This review highlights our current knowledge on ET from both a human population and mouse genetics perspective hoping to reconcile evidence from both fields and leading to novel clues guiding future studies. We argue that better communication between researchers of different fields is warranted to define the biological origin of ET in the hope of leading to the development of better treatments.
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    ABSTRACT: Essential tremor (ET) is one of the most common movement disorders. The prevalence of ET varies substantially among studies. In Korea, there is no well-designed epidemiological study of the prevalence of ET. Thus, we investigated the prevalence of ET in a community in Korea. Standardized interviews and in-person neurological examinations were performed in a random sample of the elderly aged 65 yr or older. Next, movement specialists attempted to diagnose ET clinically. People who showed equivocal parkinsonian features underwent dopamine transporter imaging using [(123)I]-FP-CIT SPECT, to differentiate ET from parkinsonism. A total of 714 subjects participated in this population-based study. Twenty six of these subjects were diagnosed as having ET. The crude prevalence of ET was 3.64 per 100 persons. Age, gender, or education period were not different between the ET patients and the non-ET subjects. The prevalence of ET was slightly lower than those reported in previous studies. Further studies including more subjects are warranted.
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    ABSTRACT: Genetic polymorphisms in Solute carrier family 1 (glial high affinity glutamate transporter), member 2 (SLC1A2) have been linked with essential tremor. SLC1A2 encodes excitatory amino acid transporter type 2 (EAAT2), which clears glutamate from the synaptic cleft. One postulated mechanism for essential tremor is the over-excitation of glutamatergic olivo-cerebellar climbing fibers, leading to excitotoxic death of Purkinje cells. Other glutamatergic excitatory signals are transmitted to Purkinje cells via parallel fibers of cerebellar granule neurons. Therefore, the expression level of glutamate transporters could be important in essential tremor pathogenesis. Using Western blotting, we compared the expression levels of the two main glutamate transporters in the cerebellar cortex, EAAT1 and EAAT2, in postmortem tissue from 16 essential tremor cases and 13 age-matched controls. We also studied the localization of EAAT1 and EAAT2 using immunohistochemistry in 10 essential tremor cases and 12 controls. EAAT1 protein levels were similar in cases and controls (1.12 ± 0.83 vs. 1.01 ± 0.69, p =0.71) whereas EAAT2 protein levels in essential tremor cases were only 1/3 of that in controls (0.35 ± 0.23 vs. 1.00 ± 0.62, p < 0.01). Interestingly, EAAT2, but not EAAT1, was expressed in astrocytic processes surrounding the Purkinje cell axon initial segment, a region of previously observed pathological changes in essential tremor. Our main finding, a significant reduction in cerebellar cortical EAAT2 protein levels in essential tremor, suggests that Purkinje cells in essential tremor might be more vulnerable to excitotoxic damage than those of controls. Electronic supplementary material The online version of this article (doi:10.1186/s40478-014-0157-z) contains supplementary material, which is available to authorized users.
    11/2014; 2(1):157. DOI:10.1186/s40478-014-0157-z

Jia Nee Foo