More unaffected first-degree relatives of essential tremor cases have mild cognitive deficits than age-matched controls

Background: In numerous case-control studies, essential tremor (ET) has been associated with cognitive impairment. ET is often familial. However, cognitive impairment has not been studied in family members of ET cases. Endophenotypes are measurable clinical characteristics that may be present in individuals with increased risk for disease; as such, they may be present before disease onset. We administered a global cognitive screen to first-degree relatives of ET cases (FD-ET) and age-matched controls (Co). Methods: We administered the Montreal Cognitive Assessment (MoCA) to 156 FD-ET and 73 Co, none of whom were diagnosed with ET or reported tremor. MoCA < 26 was considered suggestive of cognitive impairment. Results: FD-ET and Co were similar with respect to age (60.1 +/- 8.3 vs. 60.9 +/- 7.4 years) and numerous demographic factors. FD-ET and Co also had similar MoCA scores; however, 34 of 156 (21.8%) FD-ET had a MoCA score < 26 vs only 5 (6.9%) of 73 Co (p = 0.004). In a univariate logistic regression model, FD-ET were 3.79 times more likely to have a low (< 26) MoCA than were Co (odds ratio = 3.79, p = 0.008). In a multivariate logistic regression model, adjusting for age and other covariates, FD-ET were 4.83 times more likely to have a low MoCA than were Co (odds ratio = 4.83, p = 0.003). Conclusion: More FD-ET had low MoCA scores when compared with Co. These data provide additional support for the scientific notions that (1) cognitive difficulties are a disease-associated feature of ET and (2) there may be a pre-tremor phase of illness in ET.