Essential tremor in twins: an assessment of genetic vs environmental determinants of etiology.
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).


CONCLUSIONS
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.
Tanner
C M
CM
Parkinson's Institute, Sunnyvale, CA 94089, USA. ctanner@parkinsoninstitute.org
Goldman
S M
SM
Lyons
K E
KE
Aston
D A
DA
Tetrud
J W
JW
Welsh
M D
MD
Langston
J W
JW
Koller
W C
WC
D004777:Environment; D020329:Essential Tremor / Q000453:epidemiology* / Q000209:etiology / Q000235:genetics*; D020022:Genetic Predisposition to Disease; D006801:Humans; D012042:Registries; D014429:Twins, Dizygotic / Q000706:statistics & numerical data; D014430:Twins, Monozygotic / Q000706:statistics & numerical data