Prodromal Markers of First-degree Relatives of Patients With Psychiatric Disorders Comorbid With RBD

Plain-language summary

REM sleep behavior disorder (typical or 'idiopathic' RBD, iRBD) is a novel and distinct parasomnia characterized by recurrent dream enactment behaviours and polysomnographic features of loss of normal REM-sleep related muscle atonia, with a male predominance commonly occurring at the age of 60's. A majority of the patients with iRBD will eventually develop α-synucleinopathy (e.g., Parkinson's disease). On the other hand, growing evidence reveals a specific group of psychiatric patients demonstrating comparable clinical RBD features (pRBD) (e.g., abnormal REM-related electromyographic (EMG) activities) as found in typical iRBD, but with less male predominance occurring at the age of mid 40's to early 50's. Although recent findings from both cross-sectional and prospective studies have suggested that pRBD is likely to be a persistent parasomnia with close association with clinical and neuroimaging biomarkers related to neurodegeneration, the nosology of the development of RBD symptoms among patients with psychiatric disorders, notably major depressive disorder, remains unclear as to whether they are simply antidepressants related, or represent a part of the early phase of α-synucleinopathy neurodegeneration. Family studies on iRBD have confirmed a significant familial aggregation of iRBD with a higher rate of RBD cases and presence of prodromal neurodegenerative biomarkers (e.g. tonic EMG activity during REM sleep, constipation, and motor function impairments) of α-synucleinopathy neurodegeneration among first-degree relatives (FDRs) of patients with iRBD. Thus, the investigators propose this family study to examine the following hypotheses: 1) FDRs of patients with pRBD have a higher rate of RBD symptoms and its core features when compared to FDRs of controls with and without psychiatric disorders; 2) FDRs of pRBD are more likely to exhibit the features associated with prodromal markers of α-synucleinopathy neurodegeneration when compared with FDRs of controls with and without psychiatric disorders; 3) FDRs of patients with pRBD have a higher rate of α-synucleinopathy neurodegeneration when compared with FDRs of controls with and without psychiatric disorders. A total of 176 FDRs from each group (e.g., pRBD cases, psychiatric controls, and healthy controls) will be recruited to undergo a face-to-face clinical interview and a series of assessments on prodromal markers of Parkinson's diseases (as according to the International Parkinson and Movement Disorder Society research criteria) respectively. All FDRs with possible RBD and a subset of FDRs without possible RBD will be invited to undergo one-night video-polysomnographic assessment to confirm the clinical diagnosis of RBD and to assess the abnormal REM-related EMG muscle activities.

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