Clinical neurophysiology of REM parasomnias: Diagnostic aspects and insights into pathophysiology

A Narrative Review on Biochemical Markers and Emerging Treatments in Prodromal Synucleinopathies

Alpha-synuclein has been associated with neurodegeneration, especially in Parkinson's disease (PD). This study aimed to review clinical, biochemical, and neuroimaging markers and management of prodromal synucleinopathies. The prodromal state of synucleinopathies can be better understood with PD pathophysiology, and it can be separated into premotor and pre-diagnostic phases. The incidence of PD in patients with prodromal phase symptoms ranges from 0.07 to 14.30, and the most frequently studied pathology is the REM behavioral disorder (RBD). Neuroimaging markers are related to dopamine denervation, brain perfusion changes, gross anatomy changes, and peripheral abnormalities. α-synuclein assays (SAA) in CSF revealed high sensitivity (up to 97%) and high specificity (up to 92%); in the last decade, there was the development of other matrices (blood, skin, and olfactory mucosa) for obtaining quantitative and qualitative α-synuclein. Other biomarkers are neurofilament light chain, DOPA decarboxylase, and multiplexed mass spectrometry assay. Regarding genetic counseling in α-synucleinopathies, it is an important topic in clinical practice to discuss with patients with high-risk individuals and should involve basic principles of autonomy, beneficence, and non-maleficence. Some of the themes that should be reviewed are the involvement of physical activity, diet (including alcohol, coffee, and vitamin supplementation), smoking, sleep, and stress in the pathophysiology of synucleinopathies. The number of trials related to prodromal symptoms is still scarce, and the number of studies evaluating intervention is even lower.

Prediction of phenoconversion into alpha-synucleinopathy in patients with isolated REM sleep behavior disorder using event-related potentials during visuospatial attention tasks

STUDY OBJECTIVES

Isolated rapid eye movement sleep behavior disorder (iRBD) is recognized as a prodromal stage of alpha-synucleinopathies. Predicting phenoconversion in iRBD patients remains a key challenge. We aimed to investigate whether event-related potentials (ERPs) recorded during visuospatial attention tasks can serve as predictors of phenoconversion in iRBD patients.

METHODS

We conducted a longitudinal study with 126 iRBD patients (aged 67.1 ± 6.4, 77 males) and 41 healthy controls (aged 66.1 ± 6.9, 29 males). Among the patients, those who further developed synucleinopathies during the follow-up period (average 6.3 years) were classified as converters (iRBD-CV), while the others were non-converters (iRBD-NC). Posner's visuospatial cueing task was performed at baseline. The N2 and P3 components were acquired for both the cue and target (valid and invalid) stimuli. Based on group comparisons, Kaplan-Meier survival analysis was performed.

RESULTS

Twenty-nine patients converted to alpha-synucleinopathies (aged 69.4 ± 7.1, 14 males). iRBD patients exhibited overall reductions in N2 components for cue, valid, and invalid stimuli compared to HC (p = 0.012, 0.047, and 0.001, respectively). iRBD-CV patients displayed a significant increase in cue-elicited P3 (p < 0.001) and a decreasing trend in cue-elicited N2 (p = 0.079) compared to iRBD-NC. These ERP alterations were strongly associated with faster rate of phenoconversion (p < 0.001 for both components).

CONCLUSION

Our findings suggest that altered cue-elicited ERPs could serve as early biomarkers for predicting phenoconversion in iRBD patients, likely reflecting attention-related neurodegeneration pathways. These biomarkers potentially enable the detection of preclinical phenotypes in alpha-synucleinopathies, facilitating timely intervention.

From mechanisms to future therapy: a synopsis of isolated REM sleep behavior disorder as early synuclein-related disease

Parkinson disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy are synucleinopathies, characterized by neuronal loss, gliosis and the abnormal deposition of α-synuclein in vulnerable areas of the nervous system. Neurodegeneration begins however several years before clinical onset of motor, cognitive or autonomic symptoms. The isolated form of REM sleep behavior disorder (RBD), a parasomnia with dream enactment behaviors and excessive muscle activity during REM sleep, is an early stage synucleinopathy. The neurophysiological hallmark of RBD is REM sleep without atonia (RWSA), i.e. the loss of physiological muscle atonia during REM sleep. RBD pathophysiology is not fully clarified yet, but clinical and basic science suggest that ɑ-syn pathology begins in the lower brainstem where REM atonia circuits are located, including the sublaterodorsal tegmental/subcoeruleus nucleus and the ventral medulla, then propagates rostrally to brain regions such as the substantia nigra, limbic system, cortex. Genetically, there is only a partial overlap between RBD, PD and DLB, and individuals with iRBD may represent a specific subpopulation. A genome-wide association study identified five loci, which all seem to revolve around the GBA1 pathway. iRBD patients often show subtle motor, cognitive, autonomic and/or sensory signs, neuroimaging alterations as well as biofluid and tissue markers of neurodegeneration (in particular pathologic α-synuclein aggregates), which can be useful for risk stratification. Patients with iRBD represent thus the ideal population for neuroprotective/neuromodulating trials. This review provides insights into these aspects, highlighting and substantiating the central role of iRBD in treatment development strategies for synucleinopathies.

Sleep and circadian disturbances in children with neurodevelopmental disorders

Sleep is essential for brain development and overall health, particularly in children with neurodevelopmental disorders (NDDs). Sleep disruptions can considerably impact brain structure and function, leading to dysfunction of neurotransmitter systems, metabolism, hormonal balance and inflammatory processes, potentially contributing to the pathophysiology of NDDs. This Review examines the prevalence, types and mechanisms of sleep disturbances in children with NDDs, including autism spectrum disorder, attention-deficit hyperactivity disorder and various genetic syndromes. Common sleep disorders in these populations include insomnia, hypersomnia, circadian rhythm disorders, sleep-related breathing disorders and parasomnias, with underlying factors often involving genetic, neurobiological, environmental and neurophysiological influences. Sleep problems such as insomnia, night awakenings and sleep fragmentation are closely linked to both internalizing symptoms such as anxiety and depression, and externalizing behaviours such as hyperactivity and aggression. Assessment of sleep in children with NDDs presents unique challenges owing to communication difficulties, comorbid conditions and altered sensory processing. The Review underscores the importance of further research to unravel the complex interactions between sleep and neurodevelopment, advocating for longitudinal studies and the identification of predictive biomarkers. Understanding and addressing sleep disturbances in NDDs is crucial for improving developmental outcomes and the overall quality of life for affected individuals and their families.

Associations between self-reported parasomnias and psychiatric illness in 370,000 patients with sleep disorders

AIM

To assess self-reported parasomnias in patients with sleep disorders and explore relationships with psychiatric illness, comorbidities, subjective sleep assessments, and polysomnographic study results.

METHODS

Results from intake questionnaires and polysomnographic assessments, collected from 240 sleep centers across 30 US states between 2004 and 2019, were analyzed retrospectively. Of 540,000 total patients, 371,889 who answered parasomnia-specific questions were included. Patients responding "often" or "always" to parasomnia-specific questions were considered "symptom-positive," whereas a "few times" or "never" were considered "symptom-negative" (controls).

RESULTS

The study sample was 54.5% male with mean age 54 years (range, 2-107 years). Frequencies for the different parasomnias were 16.0% for any parasomnia, 8.8% for somniloquy, 6.0% for hypnagogic hallucinations, 4.8% for sleep-related eating disorder, 2.1% for sleep paralysis, and 1.7% for somnambulism. Frequent parasomnias were highly associated with diagnosed depression (odds ratio = 2.72). All parasomnias were associated with being younger and female and with symptoms of depression, anxiety, insomnia, restless legs, pain, medical conditions, fatigue, and sleepiness. Associations with objective sleep metrics showed characteristics of consolidated sleep and differentiated weakly between nonrapid eye movement sleep and rapid eye movement sleep parasomnias. Machine learning accurately classified patients with parasomnia versus controls (balanced accuracies between 71% and 79%). Benzodiazepines, antipsychotics, and opioids increased the odds of experiencing parasomnias, while antihistamines and melatonin reduced the odds. Z-drugs were found to increase the likelihood of a sleep-related eating disorder.

CONCLUSION

Our findings suggest that parasomnias may be clinically relevant, yet understudied, symptoms of depression and anxiety. Further investigation is needed to quantify the nature of multimorbidity, including causality and implications for diagnosis and treatment.

Rapid eye movement sleep behavior disorder and its relation to Parkinson's disease: The potential of graph measures as brain biomarkers to identify the underlying physiopathology of the disorder

Rapid eye movement behavior disorder (RBD) is a parasomnia characterized by the loss of skeletal muscle atonia during the rapid eye movement (REM) sleep phase. On the other hand, idiopathic RDB (iRBD) is considered the prelude of the various α-synucleinopathies, including Parkinson's disease (PD), dementia with Lewy bodies and multiple system atrophy. Consequently, over 40% of patients eventually develop PD. Recent neuroimaging studies utilizing structural magnetic resonance imaging (s-MRI), diffusion-weighted imaging (DWI), and functional magnetic resonance imaging (fMRI) with graph theoretical analysis have demonstrated that patients with iRBD and Parkinson's disease have extensive brain abnormalities. Thus, it is crucial to identify new biomarkers that aid in determining the underlying physiopathology of iRBD group. This review was conducted systematically on the included full-text articles of s-MRI, DWI, and fMRI studies using graph theoretical analysis on patients with iRBD, per the procedures recommended by Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). The literature search was conducted through the PubMed and Google scholar databases concentrating on studies from September to January 2022. Based on the three perspectives of integration, segregation, and centrality, the reviewed articles demonstrated that iRBD is associated with segregation disorders in frontal and limbic brain regions. Moreover, this study highlighted the need for additional longitudinal and multicenter studies to better understand the potential of graph metrics as brain biomarkers for identifying the underlying physiopathology of iRBD group.