REM sleep behavior disorder (RBD) represents a major and relatively specific prodromal marker for synucleinopathies such as Parkinson's disease (PD), dementia with Lewy bodies, and multisystem atrophy. Because PD patients primarily suffer from executive dysfunction, we hypothesized that individuals with RBD show an impairment in the nonamnestic executive domain rather than in amnestic domains. To address this question, we investigated a cohort of 1145 healthy elderly (183 with RBD) cross-sectionally and a subgroup of 544 of them longitudinally (144 with RBD) over 6 years. Assessments included the RBD screening questionnaire, the extended Consortium to Establish a Registry for Alzheimer's Disease test battery, and genetic testing for the risk variant rs356219 in the alpha-synuclein gene. In the cross-sectional analysis, the RBD subgroup showed worse performance in the Trail Making Test (TMT) part B and the delta-TMT_B-A when compared to non-RBD subjects. Longitudinal observation revealed a deterioration of TMT-B and delta-TMT_B-A in RBD subjects, a phenomenon that was not observed in the group of non-RBD subjects. These data argue for an early and progressive deterioration of executive dysfunction associated with RBD. Of the total cohort, 18 developed Parkinsonism including 16 with sporadic PD after a mean follow-up of 4.6 years. Of the sporadic PD cases, 4.4% were from the probable RBD group and 0.8% of the non-RBD group. The potential of this dynamic for the detection of prodromal synucleinopathies seems relevant, but has to be determined in studies including converters.
Keywords: Aging; Cognition; Cohort study; Neurodegeneration; RBD.
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