Risk of tremor and impairment from tremor in relatives of patients with essential tremor: A community-based family study

Essential tremor (ET) is a common condition that is present in as many as 2 3% of elderly individuals. Our objective was to determine the risk of ET an d to study the impairment resulting from ET among relatives of ET cases com pared to relatives of controls. ET cases and matched controls from the Wash ington Heights-Inwood community, New York, and their first- and second-degr ee relatives underwent a standardized tremor examination. The risk of havin g ET in relatives of cases vs relatives of controls was compared using Cox proportional hazards models. Five hundred ninety-one subjects were examined (59 ET cases, 72 controls, 234 case relatives, and 226 control relatives). ET was present in 25 (22.5%) of the 111 first-degree relatives of cases co mpared to 6 (5.6%) of 107 first-degree relatives of controls [relative risk (RR) = 4.67, 95% confidence interval (CI) = 1.90-11.49, p 0.0008]. RRs wer e higher in relatives of cases with onset less than or equal to 50 years th an in those with later onset (RR = 10.38 vs 4.82). Sixteen (64%) of twenty- five affected first-degree case relatives exhibited moderate tremor while p erforming tasks such as writing, drinking, or pouring. Relatives of ET pati ents are five times more likely to develop the disease than are members of the population and ten times more likely if the proband's tremor began at a n early age. The majority of the affected relatives can expect to experienc e impairment resulting from tremor.