Essential tremor in twins

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Abstract
Objective: To determine the relative contribution of genetics and environment to essential tremor using a twin study method. Methods: Twins with postural or kinetic tremor were identified by movement disorders specialists during the conduct of a study investigating PD in members of the National Academy of Sciences and National Research Council World War II Veteran Twins Registry. The diagnosis of essential tremor was made by consensus using established diagnostic criteria. Results: A total of 196 twins had postural or kinetic tremor on examination. Of these, 137 had PD or had a twin with PD and were excluded from this study. Thirty-three others were excluded because of incomplete data for their twin. Sixteen twin pairs were identified in which at least one twin had essential tremor. Pairwise concordance in monozygotic twins was approximately two times that in dizygotic twins (0.60 monozygotic, 0.27 dizygotic). Conclusion: This pattern is consistent with a genetic cause of essential tremor. Because monozygotic concordance is not 100%, environmental factors may also play a role in the cause of the disease.