ATXN8OS and Tremor: In this study, we investigated a cohort of 515 familial ET cases and 300 healthy controls with tremor-associated STR genes: ATXN1 (SCA1), ATXN2 (SCA2), ATXN3 (SCA3), CACNA1A (SCA6), ATXN7 (SCA7), ATXN8OS (SCA8), ATXN10 (SCA10), PPP2R2B (SCA12), TBP (SCA17), BEAN1 (SCA31), NOP56 (SCA36), DAB1 (SCA37), ATN1 (DRPLA), SADM12 (FAME1) and FMR1 (FXS/FXTAS), to determine whether familial ET are associated with these genes expansions, and assess the impact of expansions on these patients.