Familial versus Sporadic Essential Tremor: What Patterns Can One Decipher in Age of Onset?

Background: Essential tremor (ET) is a very prevalent neurological disease. Although familial and sporadic ET cases are assumed to have different age at onset distributions, no detailed study of this question has been carried out. Methods: Using a carefully characterized sample of 376 ET cases (232 (61.7%) familial) enrolled in a clinical-epidemiological study, we contrasted the age of onset distributions in familial versus sporadic ET. Results: Familial ET had a lower age at onset distribution, regardless of the current age. The majority (71 (86.6%) of 82) of ET cases that appeared during childhood were familial rather than sporadic. Additionally, the onset of ET occurred after age 40 in a majority of cases (125 (53.9%) of 232 with familial ET and 118 (81.9%) of 144 with sporadic ET), and in approximately one-quarter to one-half of cases, after age 60. Conclusions: The age of onset of ET differs between familial and sporadic ET and furthermore, is variable within each of these groups. The onset of ET during childhood is usually familial, and the small number of identified exceptions could be due to de novo mutations. Understanding the heterogeneity in onset age will provide insights into the nature of underlying etiological and patho-biological processes about which little is presently known.