Essential tremor (ET) is the most common tremor disorder, twenty times more prevalent than Parkinson's disease. The disease is most prevalent among individuals > 65 years of age where prevalence may be as high as 23 percent. In most clinical series, sporadic forms of the disease account for > 50 percent of the ET cases, arguing for the presence of non-genetic (environmental or occupational) causes of ET. During a previous study, which was a community-based study of the familial aggregation of ET, we developed reliable and valid methods to study ET, including questionnaires, clinical rating scales, and diagnostic criteria. Because it was not known to what extent ET clustered within families, we estimated the familial aggregation of ET. A first-degree relative of an ET case was only 3.73 times more likely to develop ET than a relative of a control subject, suggesting that non-genetic factors may contribute to the etiology of ET. However, at present, there are no studies of environmental or occupational risk factors for ET. Therefore, despite the fact that it is one of the most prevalent neurological disorders, and many of the cases appear to be non-genetic, almost nothing is known about the environmental factors which influence the risk for ET. Epidemiological data suggest that age is a risk factor for ET. Other etiologic possibilities include organochlorine pesticides (OCPs), lead, beta-carboline alkaloids. manganese, and organic solvents. We propose to further investigate the ET cases identified in our previous studies. Using a 1:1 matched case-control design, we will compare 300 ET cases receiving care for their ET at Columbia-Presbyterian Medical Center, Manhattan N.Y. to 300 normal control subjects matched by age, gender, ethnicity, and telephone exchange. Our primary aim is to evaluate the associations between three environmental or occupational exposures (OCPS, lead, beta-carboline alkaloids) and ET using biological measures and/or a lifetime Occupational History. In addition, we will evaluate the associations between manganese, organic solvents and ET using a lifetime Occupational History.
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