Rapid eye movement (REM) sleep behavior disorder (RBD) is a parasomnia characterized by dream-enactment behaviors that emerge during a loss of REM sleep atonia. RBD-related dream enactment ranges in severity from benign hand gestures to violent thrashing, punching, and kicking. In spontaneously occurring cases, RBD is a prodromal syndrome of alpha-synuclein neurodegeneration. Thus, the vast majority of RBD patients will eventually demonstrate signs and symptoms of Parkinson disease (PD) or a related disorder (e.g., multiple system atrophy or dementia with Lewy bodies), often after a prolonged interval. REM sleep without atonia (RSWA) is the hallmark of RBD and a required criterion of its diagnosis, in agreement with the International Classification of Sleep Disorders-3rd revision; however, RSWA has been reported also in subjects without RBD, as an 'incidental' finding or as an effect of antidepressants. There is preliminary observational evidence that this "isolated" RSWA might indicate an increased risk for the future development of RBD, and its occurrence with antidepressants has been interpreted as a possible indication of an acceleration of a possible underlying neurodegeneration. The scientific community is actively seeking for effective neuroprotective agents, and the very early identification of subjects at risk, years or even decades before the occurrence of a clear neurodegeneration is crucially important. The cohort constituted with this study will be able to provide extremely useful answers to this problem.

With the exception of Unit 1, which will be in charge of the implementation of the web-based electronic Clinical Report Form for the storage of data collected by all Units, the clinical work-up of all Units will be harmonized during the first 6 months of the project in order to collect, for all subjects recruited, after obtaining their informed consent, a common core of clinical and instrumental features. Unit 1 will also be in charge of the Ethics Committee procedure for the approval of the protocol, which will be accomplished during the first 3 months of activity. Particular attention will be paid to the privacy and data protection aspects of the project by involving the experts with the appropriate competences available for the activities of Unit 1 at the Oasi Research Institute (Data Protection Officer and information technology expert, in particular). Beside the definition of the inclusion/exclusion criteria and of the common core of data to collect, the recruitment of subjects will be carried-out in a period of at least 18 months by all Units, which are equipped with all necessary tools for the recording, scoring and storage of polysomnography (PSG) exams. PSG exams will be used for the identification of subjects with RSWA by means of the computation of the REM atonia index (RAI). In addition to the PSG recording, which will be performed in all subjects recruited, and in agreement with previous preliminary data produced by our groups on the possible detection of early subtle changes by means of other neurophysiological parameters , Unit 1 will also perform a transcranial magnetic stimulation (TMS) study for the evaluation of the cortical excitability of subjects found having RSWA and in an adequate group of subjects without RSWA. Similarly, Unit 2 will perform a complete Vestibular Evoked Myogenic Potentials (VEMPs) study of subjects found having RSWA and in an adequate group of subjects without RSWA, whereas Units 3 and 4 will ensure the recording of the Brainstem Auditory Evoked Potentials (BAEPs), which both evaluate the brainstem functioning. Additional instrumental exams, such as brain imaging (magnetic resonance imaging/computerized tomography scan), dopamine transporter (DAT) scan, etc., will be performed on the basis of the clinical needs of the subjects, as a part of their clinical diagnostic work-up. Finally, whenever possible and especially for subjects with RSWA, blood samples will be adequately stored for a final proteomic and metabolomic analysis in order to establish if omics signatures are expressed in them similar to those that we have already found in RBD patients .