A 7-year Prospective Study of Idiopathic REM Sleep Behavior Disorder Cohort in Chinese Population: Determining the Optimal Characteristics of Biomarkers to Predict Neurodegenerative Diseases

REM sleep behavior disorder (RBD) is a parasomnia characterized by dream enactment behaviors and REM sleep without muscle atonia (excessive EMG activity) during REM sleep.Increasing studies revealed that iRBD eventually converts to α-synucleinopathy, such as Parkinson's disease (PD), dementia with Lewy Bodies (DLB), and multiple system atrophy (MSA). Recent studies reported that over 80% of patients with iRBD eventually developed neurodegeneration at a mean interval of 14 years after iRBD onset or diagnosed. Thus, iRBD is regarded as a precursor of α-synucleinopathies. In addition to iRBD, a large series of other non-motor symptoms also present before the emergence of typical motor symptoms of PD, including autonomic dysfunction, olfactory loss, color vision impairment, neurocognitive impairment,neuroimaging of dopamine dysfunction, daytime sleepiness, and psychiatric disorders. In recent years, several longitudinal studies have found that patients with iRBD with a higher rate of these markers may have a faster progression of neurodegeneration. On the other hand, a variety of external risk factors of PD including environmental toxic exposure, lifestyle factors, and some medications have long been recognized, which affect numerous fundamental cellular processes by interaction with genetic predisposition.

However, several knowledge gaps still need further studies to uncover. First, few studies have explored the predictive value of dynamic change of biomarkers in prodromal stage of PD. Second, few previous prospective studies also employed a control group to compare the change of these prodromal markers between patients and healthy controls over time. Third, as some of previous studies employed a retrospective study design, potential recall bias may contaminate the results. Moreover, the sample sizes of most previous studies investigating biomarkers were relative small (n < 80) and follow-up durations in most study are relatively short, which may have limited the statistical power to detect the risk factors with mild to moderate effect size. Finally, as previous reported longitudinal studies of iRBD mainly focused on Caucasian or other ethnic groups, there is only limited data about neurodegenerative biomarkers in Chinese iRBD. In conclusion, prospective longitudinal studies with larger sample size, regular follow-up, and relative long follow-up duration are needed to better map the progression of neurodegeneration.