Tremor and longevity in relatives of patients with Parkinson's disease, essential tremor, and control subjects.

To study the relation between essential tremor (ET) and Parkinson's disease (PD), we compared the frequency of familial tremor in relatives of patients with PD (N = 391), ET (N = 140), and the combination of ET and PD (N = 125) with the frequency in patients with progressive supranuclear palsy (PSP) (N = 99) and normal age-matched controls (N = 104). Tremor was present in 96 (5.1%) of 1,874 parents and siblings of patients with PD, 152 of 650 (23.4%) relatives of patients with ET, 91 (20.7%) of 439 relatives of patients with ET-PD, 12 of 462 (2.6%) relatives of patients with PSP, and 10 of 448 (2.2%) relatives of normal controls. The high frequency of familial tremor among relatives of patients with PD, and especially those with the ET-PD combination, compared with relatives of patients with PSP or of normal controls suggests that there is an association of PD and familial tremor. Since the most common form of familial tremor is ET, our study provides support for the notion that ET and PD are pathogenetically related. We also found that parents with tremor lived on the average 9.2 years longer than those without tremor. The association of familial tremor with significantly increased longevity suggests that familial tremor confers some anti-aging influence. Alternatively, tremor may be a simple byproduct of the aging process.