Essential tremor in twins - An assessment of genetic vs environmental determinants of etiology

Objective: To determine the relative contribution of genetics and environme nt to essential tremor using a twin study method. Methods: Twins with postu ral or kinetic tremor were identified by movement disorders specialists dur ing the conduct of a study investigating PD in members of the National Acad emy of Sciences and National Research Council World War II Veteran Twins Re gistry. The diagnosis of essential tremor was made by consensus using estab lished diagnostic criteria. Results: A total of 196 twins had postural or k inetic tremor on examination. Of these, 137 had PD or had a twin with PD an d were excluded from this study. Thirty-three others were excluded because of incomplete data for their twin. Sixteen twin pairs were identified in wh ich at least one twin had essential tremor. Pairwise concordance in monozyg otic twins was approximately two times that in dizygotic twins (0.60 monozy gotic, 0.27 dizygotic). Conclusion: This pattern is consistent with a genet ic cause of essential tremor. Because monozygotic concordance is not 100%, environmental factors may also play a role in the cause of the disease.