Predicting age of onset in familial essential tremor: How much does age of onset run in families?

Background: The extent to which age of onset of essential tremor (ET) aggregates in families is unknown; hence, it is unclear whether information about the age of onset in one family member can be used to predict the age of onset in others. Methods: ET probands and relatives were enrolled in a genetic study at Columbia University. Results: Data from 26 probands and 52 relatives were analyzed. The probands' age of onset correlated significantly with their relatives' age of onset (r = 0.50, p = 0.001). In 57.7% of cases, the relative's age of onset was within 10 years of the proband's onset (i.e. a 20-year age range). The proportion of affected relatives with age at onset <20 years was 64.7% in the families of probands with onset younger than 20 years, but only 7.7% in the families of probands with onset ≥20 years (p < 0.001). There was little evidence for genetic anticipation; 9/18 (50.0%) children reported a younger age of onset than the proband. Conclusions: In families containing multiple individuals with ET, the age at onset of probands and relatives was significantly correlated. Age of onset may be most tightly linked in families in which the proband had a young age of onset.