Louis EK, Forsberg LK, Fields JA, Huddleston DE, Bliwise DL, Avidan AY, Howell MJ, Schenck CH, McLeland J, Criswell SR, Videnovic A, During EH, Miglis MG, Shprecher DR, Lee‐Iannotti JK, Boeve BF, Ju YS. Baseline characteristics of the North American prodromal Synucleinopathy cohort

OBJECTIVE

Rapid eye movement (REM) sleep behavior disorder (RBD) is widely considered a prodromal synucleinopathy, as most with RBD develop overt synucleinopathy within ~10 years. Accordingly, RBD offers an opportunity to test potential treatments at the earliest stages of synucleinopathy. The North American Prodromal Synucleinopathy (NAPS) Consortium has created a multisite RBD participant, primarily clinic-based cohort to better understand characteristics at diagnosis, and in future work, identify predictors of phenoconversion, develop synucleinopathy biomarkers, and enable early stage clinical trial enrollment.

METHODS

Participants ≥18 years of age with overnight polysomnogram-confirmed RBD without Parkinson's disease, dementia, multiple system atrophy, or narcolepsy were enrolled from nine sites across North America (8/2018 to 4/2021). Data collection included family/personal history of RBD and standardized assessments of cognitive, motor, sensory, and autonomic function.

RESULTS

Outcomes are primarily reported based on sex (361 total: n = 295 male, n = 66 female), and secondarily based on history of antidepressant use (n = 200 with, n = 154 without; with correction for sex differences) and based on extent of synucleinopathy burden (n = 56 defined as isolated RBD, n = 305 defined as RBD+ [i.e., exhibiting ≥1 abnormality]). Overall, these participants commonly demonstrated abnormalities in global cognition (MoCA; 38%), motor function (alternate tap test; 48%), sensory (BSIT; 57%), autonomic function (orthostatic hypotension, 38.8%), and anxiety/depression (BAI and PHQ-9; 39.3% and 31%, respectively).

INTERPRETATION

These RBD participants, assessed with extensive history, demographic, cognitive, motor, sensory, and autonomic function demonstrated a lack of sex differences and high frequency of concomitant neurological abnormalities. These participants will be valuable for future longitudinal study and neuroprotective clinical trials.

Progression of clinical markers in prodromal Parkinson's disease and dementia with Lewy bodies: a multicentre study

The neurodegenerative synucleinopathies, including Parkinson's disease and dementia with Lewy bodies, are characterized by a typically lengthy prodromal period of progressive subclinical motor and non-motor manifestations. Among these, idiopathic REM sleep behavior disorder (iRBD) is a powerful early predictor of eventual phenoconversion, and therefore represents a critical opportunity to intervene with neuroprotective therapy. To inform the design of randomized trials, it is essential to study the natural progression of clinical markers during the prodromal stages of disease in order to establish optimal clinical endpoints. In this study, we combined prospective follow-up data from 28 centers of the International REM Sleep Behavior Disorder Study Group representing 12 countries. Polysomnogram-confirmed REM sleep behavior disorder subjects were assessed for prodromal Parkinson's disease using the Movement Disorder Society criteria and underwent periodic structured sleep, motor, cognitive, autonomic and olfactory testing. We used linear mixed-effect modelling to estimate annual rates of clinical marker progression stratified by disease subtype, including prodromal Parkinson's disease and prodromal dementia with Lewy bodies. In addition, we calculated sample size requirements to demonstrate slowing of progression under different anticipated treatment effects. Overall, 1160 subjects were followed over an average of 3.3 ± 2.2 years. Among clinical variables assessed continuously, motor variables tended to progress faster and required the lowest sample sizes, ranging from 151-560 per group (at 50% drug efficacy and 2-year follow-up). By contrast, cognitive, olfactory, and autonomic variables showed modest progression with higher variability, resulting in high sample sizes. The most efficient design was a time-to-event analysis using combined milestones of motor and cognitive decline, estimating 117 per group at 50% drug efficacy and 2-year trial duration. Finally, while phenoconverters showed overall greater progression than non-converters in motor, olfactory, cognitive, and certain autonomic markers, the only robust difference in progression between Parkinson's disease and dementia with Lewy bodies phenoconverters was in cognitive testing. This large multicenter study demonstrates the evolution of motor and non-motor manifestations in prodromal synucleinopathy. These findings provide optimized clinical endpoints and sample size estimates to inform future neuroprotective trials.

NPC1 variants are not associated with Parkinson’s disease, REM-sleep behaviour disorder or Dementia with Lewy bodies in European cohorts

NPC1 encodes a lysosomal protein involved in cholesterol transport. Biallelic mutations in this gene may lead to Niemann-Pick disease type C (NPC), a lysosomal storage disorder. The role of NPC1 in alpha synucleinopathies is still unclear, as different genetic, clinical, and pathological studies have reported contradictory results. This study aimed to evaluate the association of NPC1 variants with the synucleinopathies Parkinson's disease (PD), dementia with Lewy bodies (DLB), and rapid eye movement-sleep behavior disorder (RBD). We analyzed common and rare variants from 3 cohorts of European descent: 1084 RBD cases and 2945 controls, 2852 PD cases and 1686 controls, and 2610 DLB cases and 1920 controls. Logistic regression models were used to assess common variants while optimal sequence Kernel association tests were used to assess rare variants, both adjusted for sex, age, and principal components. No variants were associated with any of the synucleinopathies, supporting that common and rare NPC1 variants do not play an important role in alpha synucleinopathies.

Dementia Risk Prediction in a Longitudinal Geriatric Parkinson's Disease Cohort: Evaluation and Application of the Montreal Parkinson Risk of Dementia Scale

Background

Parkinson's disease (PD) increases risk for dementia and cascading adverse outcomes. The eight-item Montreal Parkinson Risk of Dementia Scale (MoPaRDS) is a rapid, in-office dementia screening tool. We examine predictive validity and other characteristics of the MoPaRDS in a geriatric PD cohort by testing a series of alternative versions and modelling risk score change trajectories.

Methods

Participants were 48 initially non-demented PD patients (Mage = 71.6 years, range = 65-84) from a three-year, three-wave prospective Canadian cohort study. A dementia diagnosis at Wave 3 was used to stratify two baseline groups: PD with Incipient Dementia (PDID) and PD with No Dementia (PDND). We aimed to predict dementia three years prior to diagnosis using baseline data for eight indicators that harmonized with the original report, plus education.

Results

Three MoPaRDS items (age, orthostatic hypotension, mild cognitive impairment [MCI]) discriminated the groups both independently and as a composite three-item scale (area under the curve [AUC] = 0.88). The eight-item MoPaRDS reliably discriminated PDID from PDND (AUC = 0.81). Education did not improve predictive validity (AUC = 0.77). Performance of the eight-item MoPaRDS varied across sex (AUCfemales = 0.91; AUCmales = 0.74), whereas the three-item configuration did not (AUCfemales = 0.88; AUCmales = 0.91). Risk scores of both configurations increased over time.

Conclusions

We report new data on the application of the MoPaRDS as a dementia prediction tool for a geriatric PD cohort. Results support the viability of the full MoPaRDS, and indicate that an empirically determined brief version is a promising complement.

Challenges in the study of individuals at risk for Parkinson disease

Identifying individuals at high risk for developing neurodegenerative disease opens the possibility of conducting clinical trials that intervene at an earlier stage of neurodegeneration than has been possible to date, and in doing so hopefully improves the odds of efficacy for interventions aimed at slowing or stopping the disease process. The long prodromal phase of Parkinson disease presents opportunities and challenges to establishing cohorts of at-risk individuals. Recruiting people with genetic variants conferring increased risk and people with REM sleep behavior disorder currently constitutes the most promising strategies, but multistage screening of the general population may also be feasible capitalizing on known risk factors and prodromal features. This chapter discusses the challenges involved in identifying, recruiting, and retaining these individuals, and provides insights into possible solutions using examples from studies to date.

Genome-wide association study of REM sleep behavior disorder identifies polygenic risk and brain expression effects

Rapid-eye movement (REM) sleep behavior disorder (RBD), enactment of dreams during REM sleep, is an early clinical symptom of alpha-synucleinopathies and defines a more severe subtype. The genetic background of RBD and its underlying mechanisms are not well understood. Here, we perform a genome-wide association study of RBD, identifying five RBD risk loci near SNCA, GBA, TMEM175, INPP5F, and SCARB2. Expression analyses highlight SNCA-AS1 and potentially SCARB2 differential expression in different brain regions in RBD, with SNCA-AS1 further supported by colocalization analyses. Polygenic risk score, pathway analysis, and genetic correlations provide further insights into RBD genetics, highlighting RBD as a unique alpha-synucleinopathy subpopulation that will allow future early intervention.

Insomnia disorder increases the risk of subjective memory decline in middle-aged and older adults: a longitudinal analysis of the Canadian Longitudinal Study on Aging

STUDY OBJECTIVES

To examine the longitudinal association between probable insomnia status and both subjective and objective memory decline in middle-aged and older adults.

METHODS

26 363 participants, ≥45 years, completed baseline and follow-up (3 years after baseline) self-reported evaluations of sleep and memory, and neuropsychological testing in the following cognitive domains: memory, executive functions, and psychomotor speed. Participants were categorized as having probable insomnia disorder (PID), insomnia symptoms only (ISO), or no insomnia symptoms (NIS), based on sleep questionnaires. Participants were further grouped based on their sleep change over time. Prospective odds of self-reported memory worsening were assessed using logistic regression, and associations between insomnia and cognitive performance were assessed via linear mixed-effects modeling, adjusted for demographic, lifestyle, and medical factors.

RESULTS

An increased odds (OR 1.70; 95% CI 1.29-2.26) of self-reported memory worsening was observed for NIS participants at baseline who developed PID at follow-up compared to those who developed ISO or remained NIS. Additionally, participants whose sleep worsened from baseline to follow-up (i.e. transitioned from NIS to ISO, ISO to PID, or NIS to PID) displayed increased odds (OR 1.22; 95% CI 1.10-1.34) of subjective memory worsening at follow-up compared to those who remained insomnia-free or improved their sleep. There were no significant associations between the development of PID or worsening sleep and performance on neuropsychological tests.

CONCLUSIONS

These findings of an increased odds for subjective memory decline in middle-aged and older adults with insomnia disorder suggest insomnia may be an important target for early interventions addressing age-related cognitive decline.

From the prodromal stage of multiple sclerosis to disease prevention

A prodrome is an early set of signs or symptoms that indicate the onset of a disease before more typical symptoms develop. Prodromal stages are well recognized in some neurological and immune-mediated diseases such as Parkinson disease, schizophrenia, type 1 diabetes mellitus and rheumatoid arthritis. Emerging evidence indicates that a prodromal stage exists in multiple sclerosis (MS), raising the possibility of intervention at this stage to delay or prevent the development of classical MS. However, much remains unclear about the prodromal stage of MS and considerable research is needed to fully characterize the prodrome and develop standardized criteria to reliably identify individuals with prodromal MS who are at high risk of progressing to a diagnosis of MS. In this Roadmap, we draw on work in other diseases to propose a disease framework for MS that incorporates the prodromal stage, and set out key steps and considerations needed in future research to fully characterize the MS prodrome, identify early disease markers and develop standardized criteria that will enable reliable identification of individuals with prodromal MS, thereby facilitating trials of interventions to slow or stop progression beyond the prodrome.

Neuroprotective Trials in REM Sleep Behavior Disorder: The Way Forward Becomes Clearer

As neuroprotective therapies continue to be advanced against neurodegenerative synucleinopathies, such as Parkinson disease (PD), dementia with Lewy bodies (DLBs), and multiple system atrophy, increasing attention is turning to the prodromal stages of disease. Treatments at the prodromal stage have the compelling advantages of being applied early enough to make a meaningful difference and can be tested without confounding by symptomatic therapies used for clinical PD/DLB. As it currently stands, patients with idiopathic/isolated REM sleep behavior disorder (iRBD) represent the only large existing cohort of untreated prodromal PD/DLB that would be ready to start a clinical trial now. Several thousand patients with RBD are currently being followed in research-based clinics, and more than 80% of them will develop a full neurodegenerative synucleinopathy. Research into RBD phenoconversion rates and predictors has advanced considerably, and we are now able to generate increasingly precise estimates of progression rates, can select stratification markers to enrich trials, and are able to understand the progression and sample size implications of different primary outcome measures. This review will outline the potential for neuroprotective trials in iRBD, including the pathophysiologic mechanisms with the most promise to target in iRBD, selection criteria for inclusion, and the optimal primary trial outcome measures to choose.

Trial of Cinpanemab in Early Parkinson's Disease

BACKGROUND

Aggregated α-synuclein plays an important role in Parkinson's disease pathogenesis. Cinpanemab, a human-derived monoclonal antibody that binds to α-synuclein, is being evaluated as a disease-modifying treatment for Parkinson's disease.

METHODS

In a 52-week, multicenter, double-blind, phase 2 trial, we randomly assigned, in a 2:1:2:2 ratio, participants with early Parkinson's disease to receive intravenous infusions of placebo (control) or cinpanemab at a dose of 250 mg, 1250 mg, or 3500 mg every 4 weeks, followed by an active-treatment dose-blinded extension period for up to 112 weeks. The primary end points were the changes from baseline in the Movement Disorder Society-sponsored revision of the Unified Parkinson's Disease Rating Scale (MDS-UPDRS) total score (range, 0 to 236, with higher scores indicating worse performance) at weeks 52 and 72. Secondary end points included MDS-UPDRS subscale scores and striatal binding as assessed on dopamine transporter single-photon-emission computed tomography (DaT-SPECT).

RESULTS

Of the 357 enrolled participants, 100 were assigned to the control group, 55 to the 250-mg cinpanemab group, 102 to the 1250-mg group, and 100 to the 3500-mg group. The trial was stopped after the week 72 interim analysis owing to lack of efficacy. The change to week 52 in the MDS-UPDRS score was 10.8 points in the control group, 10.5 points in the 250-mg group, 11.3 points in the 1250-mg group, and 10.9 points in the 3500-mg group (adjusted mean difference vs. control, -0.3 points [95% confidence interval {CI}, -4.9 to 4.3], P = 0.90; 0.5 points [95% CI, -3.3 to 4.3], P = 0.80; and 0.1 point [95% CI, -3.8 to 4.0], P = 0.97, respectively). The adjusted mean difference at 72 weeks between participants who received cinpanemab through 72 weeks and the pooled group of those who started cinpanemab at 52 weeks was -0.9 points (95% CI, -5.6 to 3.8) for the 250-mg dose, 0.6 points (95% CI, -3.3 to 4.4) for the 1250-mg dose, and -0.8 points (95% CI, -4.6 to 3.0) for the 3500-mg dose. Results for secondary end points were similar to those for the primary end points. DaT-SPECT imaging at week 52 showed no differences between the control group and any cinpanemab group. The most common adverse events with cinpanemab were headache, nasopharyngitis, and falls.

CONCLUSIONS

In participants with early Parkinson's disease, the effects of cinpanemab on clinical measures of disease progression and changes in DaT-SPECT imaging did not differ from those of placebo over a 52-week period. (Funded by Biogen; SPARK ClinicalTrials.gov number, NCT03318523.).

Trial of Prasinezumab in Early-Stage Parkinson's Disease

BACKGROUND

Aggregated α-synuclein plays an important role in the pathogenesis of Parkinson's disease. The monoclonal antibody prasinezumab, directed at aggregated α-synuclein, is being studied for its effect on Parkinson's disease.

METHODS

In this phase 2 trial, we randomly assigned participants with early-stage Parkinson's disease in a 1:1:1 ratio to receive intravenous placebo or prasinezumab at a dose of 1500 mg or 4500 mg every 4 weeks for 52 weeks. The primary end point was the change from baseline to week 52 in the sum of scores on parts I, II, and III of the Movement Disorder Society-sponsored revision of the Unified Parkinson's Disease Rating Scale (MDS-UPDRS; range, 0 to 236, with higher scores indicating greater impairment). Secondary end points included the dopamine transporter levels in the putamen of the hemisphere ipsilateral to the clinically more affected side of the body, as measured by ¹²³I-ioflupane single-photon-emission computed tomography (SPECT).

RESULTS

A total of 316 participants were enrolled; 105 were assigned to receive placebo, 105 to receive 1500 mg of prasinezumab, and 106 to receive 4500 mg of prasinezumab. The baseline mean MDS-UPDRS scores were 32.0 in the placebo group, 31.5 in the 1500-mg group, and 30.8 in the 4500-mg group, and mean (±SE) changes from baseline to 52 weeks were 9.4±1.2 in the placebo group, 7.4±1.2 in the 1500-mg group (difference vs. placebo, -2.0; 80% confidence interval [CI], -4.2 to 0.2; P = 0.24), and 8.8±1.2 in the 4500-mg group (difference vs. placebo, -0.6; 80% CI, -2.8 to 1.6; P = 0.72). There was no substantial difference between the active-treatment groups and the placebo group in dopamine transporter levels on SPECT. The results for most clinical secondary end points were similar in the active-treatment groups and the placebo group. Serious adverse events occurred in 6.7% of the participants in the 1500-mg group and in 7.5% of those in the 4500-mg group; infusion reactions occurred in 19.0% and 34.0%, respectively.

CONCLUSIONS

Prasinezumab therapy had no meaningful effect on global or imaging measures of Parkinson's disease progression as compared with placebo and was associated with infusion reactions. (Funded by F. Hoffmann-La Roche and Prothena Biosciences; PASADENA ClinicalTrials.gov number, NCT03100149.).

Reliability and validity of the Roche PD Mobile Application for remote monitoring of early Parkinson's disease

Digital health technologies enable remote and therefore frequent measurement of motor signs, potentially providing reliable and valid estimates of motor sign severity and progression in Parkinson’s disease (PD). The Roche PD Mobile Application v2 was developed to measure bradykinesia, bradyphrenia and speech, tremor, gait and balance. It comprises 10 smartphone active tests (with ½ tests administered daily), as well as daily passive monitoring via a smartphone and smartwatch. It was studied in 316 early-stage PD participants who performed daily active tests at home then carried a smartphone and wore a smartwatch throughout the day for passive monitoring (study NCT03100149). Here, we report baseline data. Adherence was excellent (96.29%). All pre-specified sensor features exhibited good-to-excellent test–retest reliability (median intraclass correlation coefficient = 0.9), and correlated with corresponding Movement Disorder Society–Unified Parkinson's Disease Rating Scale items (rho: 0.12–0.71). These findings demonstrate the preliminary reliability and validity of remote at-home quantification of motor sign severity with the Roche PD Mobile Application v2 in individuals with early PD.

Brain atrophy in prodromal synucleinopathy is shaped by structural connectivity and gene expression

Isolated REM sleep behaviour disorder (iRBD) is a synucleinopathy characterized by abnormal behaviours and vocalizations during REM sleep. Most iRBD patients develop dementia with Lewy bodies, Parkinson's disease, or multiple system atrophy over time. Patients with iRBD exhibit brain atrophy patterns that are reminiscent of those observed in overt synucleinopathies. However, the mechanisms linking brain atrophy to the underlying alpha-synuclein pathophysiology are poorly understood. Our objective was to investigate how the prion-like and regional vulnerability hypotheses of alpha-synuclein might explain brain atrophy in iRBD. Using a multicentric cohort of 182 polysomnography-confirmed iRBD patients who underwent T1-weighted MRI, we performed vertex-based cortical surface and deformation-based morphometry analyses to quantify brain atrophy in patients (67.8 years, 84% men) and 261 healthy controls (66.2 years, 75%) and investigated the morphological correlates of motor and cognitive functioning in iRBD. Next, we applied the agent-based Susceptible-Infected-Removed model (i.e., a computational model that simulates in silico the spread of pathologic alpha-synuclein based on structural connectivity and gene expression) and tested if it recreated atrophy in iRBD by statistically comparing simulated regional brain atrophy to the atrophy observed in patients. The impact of SNCA and GBA gene expression and brain connectivity was then evaluated by comparing the model fit to the one obtained in null models where either gene expression or connectivity was randomized. The results showed that iRBD patients present with cortical thinning and tissue deformation, which correlated with motor and cognitive functioning. Next, we found that the computational model recreated cortical thinning (r = 0.51, p = 0.0007) and tissue deformation (r = 0.52, p = 0.0005) in patients, and that the connectome's architecture along with SNCA and GBA gene expression contributed to shaping atrophy in iRBD. We further demonstrated that the full agent-based model performed better than network measures or gene expression alone in recreating the atrophy pattern in iRBD. In summary, atrophy in iRBD is extensive, correlates with motor and cognitive function, and can be recreated using the dynamics of agent-based modelling, structural connectivity, and gene expression. These findings support the concepts that both prion-like spread and regional susceptibility account for the atrophy observed in prodromal synucleinopathies. Therefore, the agent-based Susceptible-Infected-Removed model may be a useful tool for testing hypotheses underlying neurodegenerative diseases and new therapies aimed at slowing or stopping the spread of alpha-synuclein pathology.

Rare PSAP Variants and Possible Interaction with GBA in REM Sleep Behavior Disorder

BACKGROUND

PSAP encodes saposin C, the co-activator of glucocerebrosidase, encoded by GBA. GBA mutations are associated with idiopathic/isolated REM sleep behavior disorder (iRBD), a prodromal stage of synucleinopathy.

OBJECTIVE

To examine the role of PSAP mutations in iRBD.

METHODS

We fully sequenced PSAP and performed Optimized Sequence Kernel Association Test in 1,113 iRBD patients and 2,324 controls. We identified loss-of-function (LoF) mutations, which are very rare in PSAP, in three iRBD patients and none in controls (uncorrected p = 0.018).

RESULTS

Two variants were stop mutations, p.Gln260Ter and p.Glu166Ter, and one was an in-frame deletion, p.332_333del. All three mutations have a deleterious effect on saposin C, based on in silico analysis. In addition, the two carriers of p.Glu166Ter and p.332_333del mutations also carried a GBA variant, p.Arg349Ter and p.Glu326Lys, respectively. The co-occurrence of these extremely rare PSAP LoF mutations in two (0.2%) GBA variant carriers in the iRBD cohort, is unlikely to occur by chance (estimated co-occurrence in the general population based on gnomAD data is 0.00035%). Although none of the three iRBD patients with PSAP LoF mutations have phenoconverted to an overt synucleinopathy at their last follow-up, all manifested initial signs suggestive of motor dysfunction, two were diagnosed with mild cognitive impairment and all showed prodromal clinical markers other than RBD. Their probability of prodromal PD, according to the Movement Disorder Society research criteria, was 98% or more.

CONCLUSION

These results suggest a possible role of PSAP variants in iRBD and potential genetic interaction with GBA, which requires additional studies.

Diagnostic value of cerebrospinal fluid alpha-synuclein seed quantification in synucleinopathies

Several studies have confirmed the α-synuclein real-time quaking-induced conversion (RT-QuIC) assay to have high sensitivity and specificity for Parkinson's disease. However, whether the assay can be used as a robust, quantitative measure to monitor disease progression, stratify different synucleinopathies and predict disease conversion in patients with idiopathic REM sleep behaviour disorder remains undetermined. The aim of this study was to assess the diagnostic value of CSF α-synuclein RT-QuIC quantitative parameters in regard to disease progression, stratification and conversion in synucleinopathies. We performed α-synuclein RT-QuIC in the CSF samples from 74 Parkinson's disease, 24 multiple system atrophy and 45 idiopathic REM sleep behaviour disorder patients alongside 55 healthy controls, analysing quantitative assay parameters in relation to clinical data. α-Synuclein RT-QuIC showed 89% sensitivity and 96% specificity for Parkinson's disease. There was no correlation between RT-QuIC quantitative parameters and Parkinson's disease clinical scores (e.g. Unified Parkinson's Disease Rating Scale motor), but RT-QuIC positivity and some quantitative parameters (e.g. Vmax) differed across the different phenotype clusters. RT-QuIC parameters also added value alongside standard clinical data in diagnosing Parkinson's disease. The sensitivity in multiple system atrophy was 75%, and CSF samples showed longer T50 and lower Vmax compared to Parkinson's disease. All RT-QuIC parameters correlated with worse clinical progression of multiple system atrophy (e.g. change in Unified Multiple System Atrophy Rating Scale). The overall sensitivity in idiopathic REM sleep behaviour disorder was 64%. In three of the four longitudinally followed idiopathic REM sleep behaviour disorder cohorts, we found around 90% sensitivity, but in one sample (DeNoPa) diagnosing idiopathic REM sleep behaviour disorder earlier from the community cases, this was much lower at 39%. During follow-up, 14 of 45 (31%) idiopathic REM sleep behaviour disorder patients converted to synucleinopathy with 9/14 (64%) of convertors showing baseline RT-QuIC positivity. In summary, our results showed that α-synuclein RT-QuIC adds value in diagnosing Parkinson's disease and may provide a way to distinguish variations within Parkinson's disease phenotype. However, the quantitative parameters did not correlate with disease severity in Parkinson's disease. The assay distinguished multiple system atrophy patients from Parkinson's disease patients and in contrast to Parkinson's disease, the quantitative parameters correlated with disease progression of multiple system atrophy. Our results also provided further evidence for α-synuclein RT-QuIC having potential as an early biomarker detecting synucleinopathy in idiopathic REM sleep behaviour disorder patients prior to conversion. Further analysis of longitudinally followed idiopathic REM sleep behaviour disorder patients is needed to better understand the relationship between α-synuclein RT-QuIC signature and the progression from prodromal to different synucleinopathies.

Evolution of Prodromal Multiple System Atrophy from REM Sleep Behavior Disorder: A Descriptive Study

BACKGROUND

Prodromal multiple system atrophy (MSA) has been characterized mainly by retrospective chart reviews. Direct observation and tracking of prodromal markers in MSA have been very limitedObjective:To report the baseline characteristics and evolution of prodromal markers of MSA as they were prospectively measured in patients with idiopathic/isolated REM sleep behavior disorder (iRBD)Methods:Patients with iRBD were evaluated as part of a comprehensive protocol repeated annually. The protocol included assessment of motor, sleep, psychiatric, and autonomic symptoms supplemented by motor examination, quantitative motor testing, neuropsychological examination, orthostatic blood pressure measurement, and tests of olfaction and color vision. Patients who eventually developed MSA were described and compared with those who phenoconverted to Lewy body disease (Parkinson's disease and dementia with Lewy bodies).

RESULTS

Of 67 phenocoverters, 4 developed MSA-P and 63 developed Lewy body disease. An additional 2 MSA-C patients were seen at baseline, already with cerebellar signs. Compared to those with Lewy body disease, those with MSA-P were younger, had less severe loss of tonic REM sleep atonia, more insomnia symptoms, and better olfaction. Clinically-evident autonomic dysfunction was not invariable in prodromal stages, often developing proximate to or after motor phenoconversion. Of the autonomic symptoms, genitourinary dysfunction was the first to develop in all cases. Olfaction and cognition remained normal throughout the prodromal and clinical disease course, in clear contrast to patients with Lewy body disease.

CONCLUSION

Prodromal MSA progresses rapidly, often without substantial autonomic dysfunction, and with preserved olfaction and cognition throughout its prodromal course.

Cardiovascular Risk Factors and Phenoconversion to Neurodegenerative Synucleinopathies in Idiopathic REM Sleep Behavior Disorder

Several studies have suggested that atherosclerotic diseases and diabetes may be risk factors for α-synucleinopathies. This prospective cohort study evaluated whether cardiovascular diseases and metabolic risk factors alter the rate or type of phenoconversion from idiopathic/isolated REM sleep behavior disorder (iRBD) to parkinsonism or dementia. Polysomnography-confirmed iRBD patients recruited between 2004 and 2020 were followed annually. Baseline history of cardiovascular disorders, hypertension, hypercholesterolemia, and diabetes were compared among patients who developed outcomes versus those who remained outcome-free. No atherosclerotic risk factors were associated with development of α-synucleinopathies. Patients with hypercholesterolemia were somewhat more likely to develop dementia with Lewy bodies rather than Parkinson's disease.

Preventing amyotrophic lateral sclerosis: insights from pre-symptomatic neurodegenerative diseases

Significant progress has been made in understanding the pre-symptomatic phase of amyotrophic lateral sclerosis. While much is still unknown, advances in other neurodegenerative diseases offer valuable insights. Indeed, it is increasingly clear that the well-recognized clinical syndromes of Alzheimer's disease, Parkinson's disease, Huntington's disease, spinal muscular atrophy and frontotemporal dementia are also each preceded by a pre-symptomatic or prodromal period of varying duration, during which the underlying disease process unfolds, with associated compensatory changes and loss of inherent system redundancy. Key insights from these diseases highlight opportunities for discovery in amyotrophic lateral sclerosis. The development of biomarkers reflecting amyloid and tau has led to a shift in defining Alzheimer's disease based on inferred underlying histopathology. Parkinson's disease is unique among neurodegenerative diseases in the number and diversity of non-genetic biomarkers of pre-symptomatic disease, most notably REM sleep behaviour disorder. Huntington's disease benefits from an ability to predict the likely timing of clinically manifest disease based on age and CAG-repeat length alongside reliable neuroimaging markers of atrophy. Spinal muscular atrophy clinical trials have highlighted the transformational value of early therapeutic intervention, and studies in frontotemporal dementia illustrate the differential role of biomarkers based on genotype. Similar advances in amyotrophic lateral sclerosis would transform our understanding of key events in pathogenesis, thereby dramatically accelerating progress towards disease prevention. Deciphering the biology of pre-symptomatic amyotrophic lateral sclerosis relies on a clear conceptual framework for defining the earliest stages of disease. Clinically manifest amyotrophic lateral sclerosis may emerge abruptly, especially among those who harbour genetic mutations associated with rapidly progressive amyotrophic lateral sclerosis. However, the disease may also evolve more gradually, revealing a prodromal period of mild motor impairment preceding phenoconversion to clinically manifest disease. Similarly, cognitive and behavioural impairment, when present, may emerge gradually, evolving through a prodromal period of mild cognitive impairment or mild behavioural impairment before progression to amyotrophic lateral sclerosis. Biomarkers are critically important to studying pre-symptomatic amyotrophic lateral sclerosis and essential to efforts to intervene therapeutically before clinically manifest disease emerges. The use of non-genetic biomarkers, however, presents challenges related to counselling, informed consent, communication of results and limited protections afforded by existing legislation. Experiences from pre-symptomatic genetic testing and counselling, and the legal protections against discrimination based on genetic data, may serve as a guide. Building on what we have learned-more broadly from other pre-symptomatic neurodegenerative diseases and specifically from amyotrophic lateral sclerosis gene mutation carriers-we present a road map to early intervention, and perhaps even disease prevention, for all forms of amyotrophic lateral sclerosis.

Insomnia symptom subtypes and manifestations of prodromal neurodegeneration: a population-based study in the Canadian Longitudinal Study on Aging

STUDY OBJECTIVES

To identify the association between insomnia symptoms and signs of prodromal neurodegeneration, including an analysis of potential differences between sleep-onset and sleep-maintenance insomnia.

METHODS

We included those aged 45-85 years, living in 1 of 10 Canadian provinces between 2012 and 2015 (at the baseline), recruited via 3 population-based sampling methods. Insomnia symptoms were assessed using questions adapted/modified from the Pittsburgh Sleep Quality Index. A panel of potential prodromal neurodegenerative markers including self-reported symptoms and objective gait motor, cognitive, and autonomic variables were assessed cross sectionally. We compared those who endorsed insomnia symptoms ≥ 3 times per week to controls, adjusting for age, sex, and education via logistic regression.

RESULTS

Overall, 2,051/30,097 people screened positive for sleep-onset insomnia alone and 4,333 for sleep-maintenance insomnia alone, while 2,371 endorsed both subtypes. On objective gait tests, participants with sleep-onset insomnia, but not sleep-maintenance insomnia, had worse balance (odds ratio [OR] = 1.33, 95% confidence interval = [1.16, 1.52]) and slower gait speed (OR = 1.52 [1.34, 1.73]). Although participants with any insomnia subtype endorsed more motor symptoms, these were more severe in those with sleep-onset insomnia (OR onset vs maintenance = 1.13 [1.07, 1.18]). On objective cognitive tests, those with sleep-maintenance insomnia scored normally. However, participants with sleep-onset insomnia performed worse on tests of verbal fluency (OR = 1.24 [1.06, 1.43]), immediate memory (OR = 1.23 [1.08, 1.41]), and prospective memory task (OR = 1.29 [1.11, 1.50]). The sleep-onset insomnia group also had lower heart rate variability (OR = 1.23 [1.07, 1.43]). Secondary analyses found generally similar results in young vs older age of insomnia development.

CONCLUSIONS

Compared to maintenance insomnia, those with sleep-onset insomnia have more motor, cognitive, and autonomic signs/symptoms. When evaluating neurodegenerative risk, differentiating insomnia subtypes may increase precision.

CITATION

Yao CW, Pelletier A, Fereshtehnejad S-M, Cross N, Dang-Vu T, Postuma RB. Insomnia symptom subtypes and manifestations of prodromal neurodegeneration: a population-based study in the Canadian Longitudinal Study on Aging. J Clin Sleep Med. 2022;18(2):345-359.

Association of Essential Tremor With Novel Risk Loci: A Genome-Wide Association Study and Meta-analysis

Question

Can common genetic variants associated with essential tremor (ET) be identified?

Findings

In this genome-wide association study and meta-analysis including genetic data on 483 054 individuals, 5 genome-wide significant loci were associated with risk of ET and common variants were associated with approximately 18% of ET heritability.

Meaning

Findings of this study may help identify new genes and inform ET biology.

Importance

Essential tremor (ET) is one of the most common movement disorders, affecting 5% of the general population older than 65 years. Common variants are thought to contribute toward susceptibility to ET, but no variants have been robustly identified.

Objective

To identify common genetic factors associated with risk of ET.

Design, Setting, and Participants

Case-control genome-wide association study. Inverse-variance meta-analysis was used to combine cohorts. Multicenter samples collected from European populations were collected from January 2010 to September 2019 as part of an ongoing study. Included patients were clinically diagnosed with or reported having ET. Control individuals were not diagnosed with or reported to have ET. Of 485 250 individuals, data for 483 054 passed data quality control and were used.

Main Outcomes and Measures

Genotypes of common variants associated with risk of ET.

Results

Of the 483 054 individuals included, there were 7177 with ET (3693 [51.46%] female; mean [SD] age, 62.66 [15.12] years), and 475 877 control individuals (253 785 [53.33%] female; mean [SD] age, 56.40 [17.6] years). Five independent genome-wide significant loci and were identified and were associated with approximately 18% of ET heritability. Functional analyses found significant enrichment in the cerebellar hemisphere, cerebellum, and axonogenesis pathways. Genetic correlation (r), which measures the degree of genetic overlap, revealed significant common variant overlap with Parkinson disease (r, 0.28; P = 2.38 × 10⁻⁸) and depression (r, 0.12; P = 9.78 × 10⁻⁴). A separate fine-mapping of transcriptome-wide association hits identified genes such as BACE2, LRRN2, DHRS13, and LINC00323 in disease-relevant brain regions, such as the cerebellum.

Conclusions and Relevance

The results of this genome-wide association study suggest that a portion of ET heritability can be explained by common genetic variation and can help identify new common genetic risk factors for ET.