Prevalence of asymptomatic tremor in relatives of patients with essential tremor

Background: The extent to which essential tremor (ET) clusters within families (ie, the familial aggregation of ET) is not precisely known. In part, this is because studies assign disease status in relatives of patients with ET based solely on interviews without conducting physical examinations. This may lead to underascertainment of affected relatives with mild asymptomatic ET. Objective: To determine the prevalence of asymptomatic ET among relatives of patients with ET. Methods: Interview and examination of 25 patients with ET and 58 of their relatives. The interview included 12 questions that screened the patients for ET. Two neurologists who specialize in movement disorders reviewed the videotaped examinations. Based on standardized criteria, diagnoses included ET (definite, probable, or possible) or normal. Results: Of the 8 relatives who received diagnoses of ET, 5 (62.5%) had asymptomatic ET. Hence, 5 (8.6%) of the 58 relatives (95% confidence interval, 1.4%-15.8%) had asymptomatic ET. In those with asymptomatic ET, there was a preponderance of young individuals with mild tremor in the nondominant band. Conclusions: The prevalence of asymptomatic ET in relatives of patients with ET was similar to that of symptomatic ET. Family studies that do not perform both an interview and a physical examination will underascertain the number of affected relatives. Therefore, future family studies should evaluate relatives of patients with ET with an interview supplemented by a physical examination.