MicroRNA Deregulation in Blood Serum Identifies Multiple System Atrophy Altered Pathways.

BACKGROUND AND OBJECTIVES: MicroRNA (miRNA) changes are observed in PD but remain poorly explored in other α-synucleinopathies such as MSA. METHODS: By genome-wide analysis we profiled microRNA expression in serum from 20 MSA cases compared to 40 controls. By qPCR we validated top differentially expressed microRNAs in another sample of 20 MSA and 20 controls. We also assessed the expression of MSA differentially expressed microRNAs in two consecutive sets of 19 and 18 PD patients. RESULTS: In the discovery set we identified 25 differentially expressed microRNAs associated with MSA, which are related to prion disease, fatty acid metabolism, and Notch signaling. Among these, we selected nine differentially expressed microRNAs and by qPCR confirmed array findings in a second MSA sample. MicroRNA-7641 and microRNA-191 consistently differentiated between MSA and PD. CONCLUSIONS: Serum microRNA changes occur in MSA and may reflect disease-associated mechanisms. We identified two microRNAs which may differentiate MSA from PD. © 2020 International Parkinson and Movement Disorder Society.

Lack of Asymmetry of Nigrostriatal Dopaminergic Function in Healthy Subjects.

OBJECTIVE: In right-handed patients with Parkinson's disease (PD) or isolated rapid eye movement sleep behavior disorder, dopamine transporter (DAT) [(123)I]ß-carboxymethyoxy-3-ß-(4-iodophenyl) tropane single photon emission computed tomography (SPECT) shows predominant nigrostriatal deficit in the left striatum. This suggests that in PD patients, the nigrostriatal system of the dominant hemisphere is more susceptible to disease-related dysfunction. To confirm this hypothesis, we investigated whether the nigrostriatal function is symmetric in healthy controls and in patients with PD. METHODS: In 113 right-handed healthy controls and 279 right-handed early-PD patients, we examined the striatal dopaminergic terminals function in each hemisphere using DAT-SPECT. RESULTS: In the controls, DAT-SPECT showed symmetric specific binding ratios in the putamen and caudate nucleus of each hemisphere. In patients with PD, the specific binding ratio was lower in the left than in the right putamen. CONCLUSIONS: Right-handed healthy controls have symmetric nigrostriatal dopaminergic function. The left hemispheric predominance of nigrostriatal deficit seen in right-handed premotor and manifest PD represents an early pathological feature of the disease. © 2020 International Parkinson and Movement Disorder Society.

SNCA and mTOR Pathway Single Nucleotide Polymorphisms Interact to Modulate the Age at Onset of Parkinson's Disease.

BACKGROUND: Single nucleotide polymorphisms (SNPs) in the α-synuclein (SNCA) gene are associated with differential risk and age at onset (AAO) of both idiopathic and Leucine-rich repeat kinase 2 (LRRK2)-associated Parkinson's disease (PD). Yet potential combinatory or synergistic effects among several modulatory SNPs for PD risk or AAO remain largely underexplored. OBJECTIVES: The mechanistic target of rapamycin (mTOR) signaling pathway is functionally impaired in PD. Here we explored whether SNPs in the mTOR pathway, alone or by epistatic interaction with known susceptibility factors, can modulate PD risk and AAO. METHODS: Based on functional relevance, we selected a total of 64 SNPs mapping to a total of 57 genes from the mTOR pathway and genotyped a discovery series cohort encompassing 898 PD patients and 921 controls. As a replication series, we screened 4170 PD and 3014 controls available from the International Parkinson's Disease Genomics Consortium. RESULTS: In the discovery series cohort, we found a 4-loci interaction involving STK11 rs8111699, FCHSD1 rs456998, GSK3B rs1732170, and SNCA rs356219, which was associated with an increased risk of PD (odds ratio = 2.59, P < .001). In addition, we also found a 3-loci epistatic combination of RPTOR rs11868112 and RPS6KA2 rs6456121 with SNCA rs356219, which was associated (odds ratio = 2.89; P < .0001) with differential AAO. The latter was further validated (odds ratio = 1.56; P = 0.046-0.047) in the International Parkinson's Disease Genomics Consortium cohort. CONCLUSIONS: These findings indicate that genetic variability in the mTOR pathway contributes to SNCA effects in a nonlinear epistatic manner to modulate differential AAO in PD, unraveling the contribution of this cascade in the pathogenesis of the disease. © 2019 International Parkinson and Movement Disorder Society.

The Genetic Architecture of Parkinson Disease in Spain: Characterizing Population-Specific Risk, Differential Haplotype Structures, and Providing Etiologic Insight.

BACKGROUND: The Iberian Peninsula stands out as having variable levels of population admixture and isolation, making Spain an interesting setting for studying the genetic architecture of neurodegenerative diseases. OBJECTIVES: To perform the largest PD genome-wide association study restricted to a single country. METHODS: We performed a GWAS for both risk of PD and age at onset in 7,849 Spanish individuals. Further analyses included population-specific risk haplotype assessments, polygenic risk scoring through machine learning, Mendelian randomization of expression, and methylation data to gain insight into disease-associated loci, heritability estimates, genetic correlations, and burden analyses. RESULTS: We identified a novel population-specific genome-wide association study signal at PARK2 associated with age at onset, which was likely dependent on the c.155delA mutation. We replicated four genome-wide independent signals associated with PD risk, including SNCA, LRRK2, KANSL1/MAPT, and HLA-DQB1. A significant trend for smaller risk haplotypes at known loci was found compared to similar studies of non-Spanish origin. Seventeen PD-related genes showed functional consequence by two-sample Mendelian randomization in expression and methylation data sets. Long runs of homozygosity at 28 known genes/loci were found to be enriched in cases versus controls. CONCLUSIONS: Our data demonstrate the utility of the Spanish risk haplotype substructure for future fine-mapping efforts, showing how leveraging unique and diverse population histories can benefit genetic studies of complex diseases. The present study points to PARK2 as a major hallmark of PD etiology in Spain. © 2019 International Parkinson and Movement Disorder Society.

Exhaustion of mitochondrial and autophagic reserve may contribute to the development of LRRK2 G2019S -Parkinson's disease.

BACKGROUND: Mutations in leucine rich repeat kinase 2 (LRRK2) are the most common cause of familial Parkinson's disease (PD). Mitochondrial and autophagic dysfunction has been described as etiologic factors in different experimental models of PD. We aimed to study the role of mitochondria and autophagy in LRRK2 G2019S -mutation, and its relationship with the presence of PD-symptoms. METHODS: Fibroblasts from six non-manifesting LRRK2 G2019S -carriers (NM-LRRK2 G2019S ) and seven patients with LRRK2 G2019S -associated PD (PD-LRRK2 G2019S ) were compared to eight healthy controls (C). An exhaustive assessment of mitochondrial performance and autophagy was performed after 24-h exposure to standard (glucose) or mitochondrial-challenging environment (galactose), where mitochondrial and autophagy impairment may be heightened. RESULTS: A similar mitochondrial phenotype of NM-LRRK2 G2019S and controls, except for an early mitochondrial depolarization (54.14% increased, p = 0.04), was shown in glucose. In response to galactose, mitochondrial dynamics of NM-LRRK2 G2019S improved (- 17.54% circularity, p = 0.002 and + 42.53% form factor, p = 0.051), probably to maintain ATP levels over controls. A compromised bioenergetic function was suggested in PD-LRRK2 G2019S when compared to controls in glucose media. An inefficient response to galactose and worsened mitochondrial dynamics (- 37.7% mitochondrial elongation, p = 0.053) was shown, leading to increased oxidative stress. Autophagy initiation (SQTSM/P62) was upregulated in NM-LRRK2 G2019S when compared to controls (glucose + 118.4%, p = 0.014; galactose + 114.44%, p = 0.009,) and autophagosome formation increased in glucose media. Despite of elevated SQSTM1/P62 levels of PD-NM G2019S when compared to controls (glucose + 226.14%, p = 0.04; galactose + 78.5%, p = 0.02), autophagosome formation was deficient in PD-LRRK2 G2019S when compared to NM-LRRK2 G2019S (- 71.26%, p = 0.022). CONCLUSIONS: Enhanced mitochondrial performance of NM-LRRK2 G2019S in mitochondrial-challenging conditions and upregulation of autophagy suggests that an exhaustion of mitochondrial bioenergetic and autophagic reserve, may contribute to the development of PD in LRRK2 G2019S mutation carriers.

Dopamine transporter imaging deficit predicts early transition to synucleinopathy in idiopathic rapid eye movement sleep behavior disorder.

OBJECTIVE: To determine the usefulness of dopamine transporter (DAT) imaging to identify idiopathic rapid eye movement sleep behavior disorder (IRBD) patients at risk for short-term development of clinically defined synucleinopathy. METHODS: Eighty-seven patients with polysomnography-confirmed IRBD underwent 123 I-FP-CIT DAT-SPECT. Results were compared to 20 matched controls without RBD who underwent DAT-SPECT. In patients, FP-CIT uptake was considered abnormal when values were two standard deviations below controls' mean uptake. After DAT-SPECT, patients were followed up during 5.7 ± 2.2 (range, 2.6-9.9) years. RESULTS: Baseline DAT deficit was found in 51 (58.6%) patients. During follow-up, 25 (28.7%) subjects developed clinically defined synucleinopathy (Parkinson's disease in 11, dementia with Lewy bodies in 13, and multiple system atrophy in 1) with mean latency of 3.2 ± 1.9 years from imaging. Kaplan-Meier survival analysis showed increased risk of incident synucleinopathy in patients with abnormal DAT-SPECT than with normal DAT-SPECT (20% vs 6% at 3 years, 33% vs 18% at 5 years; log rank test, p = 0.006). Receiver operating characteristics curve revealed that reduction of FP-CIT uptake in putamen greater than 25% discriminated patients with DAT deficit who developed synucleinopathy from patients with DAT deficit that remained disease free after 3 years of follow-up. At 5-year follow-up, DAT-SPECT had 75% sensitivity, 51% specificity, 44% positive predictive value, 80% negative predictive value, and likelihood ratio 1.54 to predict synucleinopathy. INTERPRETATION: DAT-SPECT identifies IRBD patients at short-term risk for synucleinopathy. Decreased FP-CIT putamen uptake greater than 25% predicts synucleinopathy after 3 years' follow-up. These observations may be useful to select candidates for disease modification trials in IRBD. Ann Neurol 2017;82:419-428.

Mitochondrial DNA in CSF distinguishes LRRK2 from idiopathic Parkinson's disease.

Mitochondrial DNA regulates mitochondrial function which is altered in both idiopathic and familial forms of Parkinson's disease. To investigate whether these two disease forms exhibit an altered regulation of mitochondrial DNA we measured cell free mitochondrial DNA content in cerebrospinal fluid (CSF) from idiopathic and LRRK2-related Parkinson's disease patients. The concentration of mitochondrial DNA was measured using a digital droplet polymerase chain reaction technique in a total of 98 CSF samples from a cohort of subjects including: 20 LRRK2(G2019S) mutation carriers with Parkinson's disease, 26 asymptomatic LRRK2(G2019S) mutation carriers, 31 patients with idiopathic Parkinson's disease and 21 first-degree relatives of LRRK2 Parkinson's disease patients without the mutation. Here we report that LRRK2(G2019S) mutation carriers with Parkinson's disease exhibit a high concentration of mitochondrial DNA in CSF compared with asymptomatic LRRK2(G2019S) mutation carriers and with idiopathic Parkinson's disease patients. In addition, idiopathic, but not LRRK2 Parkinson's disease is associated with low CSF concentration of α-synuclein. These results show that high mitochondrial DNA content in CSF distinguishes idiopathic from LRRK2-related Parkinson's disease suggesting that different biochemical pathways underlie neurodegeneration in these two disorders.

Cutaneous autonomic denervation in Parkinson's disease.

Numerous studies have detailed involvement of the peripheral autonomic nervous system (PANS) in Parkinson's disease (PD). We assessed autonomic innervation of dermal annexes through quantitative fluorescence measurement from skin obtained via punch biopsies at distal leg region in PD and control subjects. We defined a ratio between the area corresponding to protein gen product (PGP) immunoreactivity and the area corresponding to blood vessel or sweat gland as a quantitative measure of autonomic innervation. Presence of alpha-synuclein (AS) deposits in dermis and hypodermis was also assessed by immunohistochemistry. Skin biopsies form six PD patients and six healthy controls were studied. Autonomic innervation scores were lower in PD than in controls in both blood vessels and sweat glands. No AS or phosphorylated AS (pAS) immunoreactivity was detected in dermis or hypodermis in any of the studied subjects. The results of this investigation suggest that autonomic innervation of dermal annexes in living patients with PD is reduced compared to controls. AS or pAS deposits were not found in dermis or hypodermis suggesting that distal leg skin study is not useful for in vivo detection of AS in PD.

Neuropathology of prodromal Lewy body disease.

BACKGROUND: Current evidence suggests that there is a prodromal stage in Parkinson disease characterized by a variety of nonmotor symptoms. METHODS AND RESULTS: A 69-year-old man presented to our sleep center with isolated rapid eye movement sleep behavior disorder. During a 10-year follow-up period, longitudinal clinical and laboratory assessments indicated the development of hyposmia, depression, mild cognitive impairment, and constipation. Parkinsonism was absent, but dopamine transporter imaging showed subclinical substantia nigra damage. Postmortem examination demonstrated neuronal loss and Lewy body pathology in the peripheral autonomic nervous system (eg, cardiac and myenteric plexus), olfactory bulb, medulla, pons, substantia nigra pars compacta (estimated cell loss, 20%-30%), nucleus basalis of Meynert, and amygdala, sparing the neocortex. CONCLUSIONS: Our observations indicate that nonmotor symptoms plus widespread peripheral and central nervous system pathological changes occur before parkinsonism and dementia onset in diseases associated with Lewy pathology. The current diagnostic criteria for Parkinson's disease miss these patients, who present only with nonmotor symptoms.

Five-year follow-up of substantia nigra echogenicity in idiopathic REM sleep behavior disorder.

Hyperechogenicity of the substantia nigra visualized by transcranial sonography occurs in most Parkinson's disease (PD) patients. Idiopathic rapid eye movement (REM) sleep behavior disorder (IRBD) subjects eventually develop PD and other synucleinopathies. This study was undertaken to evaluate whether in IRBD, transcranial sonography identifies subjects who convert to PD and other synucleinopathies, and whether substantia nigra echogenic size changes with time. It was a prospective study in which 55 IRBD patients underwent transcranial sonography at baseline and were invited to follow-up after 5 years. Patients were assessed by the same experienced sonographer who was blinded to clinical data and baseline transcranial sonography results, and used the same equipment and adjustments. Twenty-one (38.2%) subjects were diagnosed with a synucleinopathy (PD in 11, dementia with Lewy bodies in nine, and multiple system atrophy in one). Sensitivity of baseline substantia nigra hyperechogenicity for the development of a synucleinopathy was 42.1%, specificity 67.7%, positive predictive value 44.4%, negative predictive value 65.6%, and relative risk 1.29. No differences were detected between the first and second examination in mean size of the substantia nigra (0.20 ± 0.09 cm(2) vs. 0.19 ± 0.07 cm(2) ; P = 0.777) and in percentage of patients with substantia nigra hyperechogenicity (33.3% vs. 42.8%, P = 0.125). Transcranial sonography of the substantia nigra alone is not a useful tool to identify IRBD subjects at risk for the development of PD or a synucleinopathy after 5 years of follow-up. In IRBD, transcranial sonography cannot be used to monitor the degenerative process in the substantia nigra, because echogenicity size remains stable over time.

Mitochondrial DNA deletions in the cerebrospinal fluid of patients with idiopathic REM sleep behaviour disorder.

BACKGROUND: Idiopathic rapid eye movement (REM) sleep behaviour disorder (IRBD) represents the prodromal stage of Lewy body disorders (Parkinson's disease (PD) and dementia with Lewy bodies (DLB)) which are linked to variations in circulating cell-free mitochondrial DNA (cf-mtDNA). Here, we assessed whether altered cf-mtDNA release and integrity are already present in IRBD. METHODS: We used multiplex digital PCR (dPCR) to quantify cf-mtDNA copies and deletion ratio in cerebrospinal fluid (CSF) and serum in a cohort of 71 participants, including 1) 17 patients with IRBD who remained disease-free (non-converters), 2) 34 patients initially diagnosed with IRBD who later developed either PD or DLB (converters), and 3) 20 age-matched controls without IRBD or Parkinsonism. In addition, we investigated whether CD9-positive extracellular vesicles (CD9-EVs) from CSF and serum samples contained cf-mtDNA. FINDINGS: Patients with IRBD, both converters and non-converters, exhibited more cf-mtDNA with deletions in the CSF than controls. This finding was confirmed in CD9-EVs. The high levels of deleted cf-mtDNA in CSF corresponded to a significant decrease in cf-mtDNA copies in CD9-EVs in both IRBD non-converters and converters. Conversely, a significant increase in cf-mtDNA copies was found in serum and CD9-EVs from the serum of patients with IRBD who later converted to a Lewy body disorder. INTERPRETATION: Alterations in cf-mtDNA copy number and deletion ratio known to occur in Lewy body disorders are already present in IRBD and are not a consequence of Lewy body disease conversion. This suggests that mtDNA dysfunction is a primary molecular mechanism of the pathophysiological cascade that precedes the full clinical motor and cognitive manifestation of Lewy body disorders. FUNDING: Funded by Michael J. Fox Foundation research grant MJFF-001111. Funded by MICIU/AEI/10.13039/501100011033 "ERDF A way of making Europe", grants PID2020-115091RB-I00 (RT) and PID2022-143279OB-I00 (ACo). Funded by Instituto de Salud Carlos III and European Union NextGenerationEU/PRTR, grant PMP22/00100 (RT and ACo). Funded by AGAUR/Generalitat de Catalunya, grant SGR00490 (RT and ACo). MP has an FPI fellowship, PRE2018-083297, funded by MICIU/AEI/10.13039/501100011033 "ESF Investing in your future".

Progressive changes in a recognition memory network in Parkinson's disease.

BACKGROUND: In a previous functional MRI (fMRI) study, we found that patients with Parkinson's disease (PD) presented with dysfunctions in the recruitment of recognition memory networks. We aimed to investigate the changes in these networks over time. METHODS: We studied 17 PD patients and 13 age and sex matched healthy subjects. In both groups fMRI (recognition memory paradigm) and neuropsychological assessments were obtained at baseline and at follow-up. To analyse changes over time in functional networks, model free (independent component analysis) analyses of the fMRI data were carried out. Then, a cross correlation approach was used to assess the changes in the strength of functional connectivity. RESULTS: At follow-up, patients showed reduced recruitment of one network, including decreased activation in the orbitofrontal cortices, middle frontal gyri, frontal poles, anterior paracingulate cortex, superior parietal lobes and left middle temporal gyrus, as well as decreased deactivation in the anterior paracingulate gyrus and precuneus. Cross correlation analyses over time showed a decrease in the strength of functional connectivity between the middle frontal gyrus and the superior parietal lobe in PD patients. CONCLUSIONS: Model free fMRI and cross correlation connectivity analyses were able to detect progressive changes in functional networks involved in recognition memory in PD patients at early disease stages and without overt clinical deterioration. Functional connectivity analyses could be useful to monitor changes in brain networks underlying neuropsychological deficits in PD.

Microarray expression analysis in idiopathic and LRRK2-associated Parkinson's disease.

LRRK2 mutations are the most common genetic cause of Parkinson's disease (PD). We performed a whole-genome RNA profiling of putamen tissue from idiopathic PD (IPD), LRRK2-associated PD (G2019S mutation), neurologically healthy controls and one asymptomatic LRRK2 mutation carrier, by using the Genechip Human Exon 1.0-ST Array. The differentially expressed genes found in IPD revealed an alteration of biological pathways related to long-term potentiation (LTP), GABA receptor signalling, and calcium signalling pathways, among others. These pathways are mainly related with cell signalling cascades and synaptic plasticity processes. They were also altered in the asymptomatic LRRK2 mutation carrier but not in the LRRK2-associated PD group. The expression changes seen in IPD might be attributed to an adaptive consequence of a dysfunction in the dopamine transmission. The lack of these altered molecular pathways in LRRK2-associated PD patients suggests that these cases could show a different molecular response to dopamine transmission impairment.

Magnetic resonance imaging abnormalities as a marker of multiple system atrophy in isolated rapid eye movement sleep behavior disorder.

STUDY OBJECTIVES: Patients with isolated rapid eye movement (REM) sleep behavior disorder (IRBD) develop Parkinson disease (PD), dementia with Lewy bodies (DLB), or multiple system atrophy (MSA). Magnetic resonance imaging (MRI) is abnormal in MSA showing abnormalities in the putamen, cerebellum, and brainstem. Our objective was to evaluate the usefulness of MRI to detect MRI abnormalities in IRBD and predict development of MSA and not PD and DLB. METHODS: In IRBD patients that eventually developed PD, DLB, and MSA, we looked for the specific structural MRI abnormalities described in manifest MSA (e.g. hot cross-bun sign, putaminal rim, and cerebellar atrophy). We compared the frequency of these MRI changes among groups of converters (PD, DLB, and MSA) and analyzed their ability to predict development of MSA. The clinical and radiological features of the IRBD patients that eventually converted to MSA are described in detail. RESULTS: A total of 61 IRBD patients who underwent MRI phenoconverted to PD (n = 30), DLB (n = 26), and MSA (n = 5) after a median follow-up of 2.4 years from neuroimaging. MRI changes typical of MSA were found in four of the five (80%) patients who converted to MSA and in three of the 56 (5.4%) patients who developed PD or DLB. MRI changes of MSA had sensitivity of 80.0%, specificity of 94.6%, positive likelihood ratio of 14.9 (95% CI 4.6-48.8), and negative likelihood ratio of 0.2 (95% CI 0.04-1.2) to predict MSA. CONCLUSIONS: In IRBD, conventional brain MRI is helpful to predict conversion to MSA. The specific MRI abnormalities of manifest MSA may be detected in its premotor stage.

Detection of α-synuclein in CSF by RT-QuIC in patients with isolated rapid-eye-movement sleep behaviour disorder: a longitudinal observational study.

BACKGROUND: Isolated rapid-eye-movement (REM) sleep behaviour disorder (IRBD) can be part of the prodromal stage of the α-synucleinopathies Parkinson's disease and dementia with Lewy bodies. Real-time quaking-induced conversion (RT-QuIC) analysis of CSF has high sensitivity and specificity for the detection of misfolded α-synuclein in patients with Parkinson's disease and dementia with Lewy bodies. We investigated whether RT-QuIC could detect α-synuclein in the CSF of patients with IRBD and be used as a biomarker of prodromal α-synucleinopathy. METHODS: In this longitudinal observational study, CSF samples were obtained by lumbar puncture from patients with video polysomnography-confirmed IRBD recruited at a specialised sleep disorders centre in Barcelona, Spain, and from controls free of neurological disease. CSF samples were stored until analysed using RT-QuIC. After lumbar puncture, participants were assessed clinically for neurological status every 3-12 months. Rates of neurological disease-free survival were estimated using the Kaplan-Meier method. Disease-free survival rates were assessed from the date of lumbar puncture to the date of diagnosis of any neurodegenerative disease, or to the last follow-up visit for censored observations. FINDINGS: 52 patients with IRBD and 40 healthy controls matched for age (p=0·20), sex (p=0·15), and duration of follow-up (p=0·27) underwent lumbar puncture between March 23, 2008, and July 16, 2017. The CSF α-synuclein RT-QuIC assay was positive in 47 (90%) patients with IRBD and in four (10%) controls, resulting in a sensitivity of 90·4% (95% CI 79·4-95·8) and a specificity of 90·0% (95% CI 76·9-96·0). Mean follow-up from lumbar puncture until the end of the study (July 31, 2020) was 7·1 years (SD 2·8) in patients with IRBD and 7·7 years (2·9) in controls. During follow-up, 32 (62%) patients were diagnosed with Parkinson's disease or dementia with Lewy bodies a mean 3·4 years (SD 2·6) after lumbar puncture, of whom 31 (97%) were α-synuclein positive at baseline. Kaplan-Meier analysis showed that patients with IRBD who were α-synuclein negative had lower risk for developing Parkinson's disease or dementia with Lewy bodies at 2, 4, 6, 8, and 10 years of follow-up than patients with IRBD who were α-synuclein positive (log-rank test p=0·028; hazard ratio 0·143, 95% CI 0·019-1·063). During follow-up, none of the controls developed an α-synucleinopathy. Kaplan-Meier analysis showed that participants who were α-synuclein negative (ie, five patients with IRBD plus 36 controls) had lower risk of developing Parkinson's disease or dementia with Lewy bodies at 2, 4, 6, 8 and 10 years after lumbar puncture than participants who were α-synuclein positive (ie, 47 patients with IRBD plus four controls; log-rank test p<0·0001; hazard ratio 0·024, 95% CI 0·003-0·177). INTERPRETATION: In patients with IRBD, RT-QuIC detects misfolded α-synuclein in the CSF with both sensitivity and specificity of 90%, and α-synuclein positivity was associated with increased risk of subsequent diagnosis of Parkinson's disease or dementia with Lewy bodies. Detection of α-synuclein in the CSF represents a potential prodromal marker of Parkinson's disease and dementia with Lewy bodies. If these findings are replicated in additional cohorts, detection of CSF α-synuclein by RT-QuIC could be used to enrich IRBD cohorts in neuroprotective trials, particularly when assessing interventions that target α-synuclein. FUNDING: Department of Health and Social Care Policy Research Programme, the Scottish Government, and the Weston Brain Institute.

Exome-wide rare variant analysis in familial essential tremor.

INTRODUCTION: Essential tremor (ET) is one of the most common movement disorders. Despite its high prevalence and heritability, its genetic etiology remains elusive with only a few susceptibility genes identified and poorly replicated. Our aim was to find novel candidate genes involved in ET predisposition through whole exome sequencing. METHODS: We studied eight multigenerational families (N = 40 individuals) with an autosomal-dominant inheritance using a comprehensive strategy combining whole exome sequencing followed by case-control association testing of prioritized variants in a separate cohort comprising 521 ET cases and 596 controls. We further performed gene-based burden analyses in an additional dataset comprising 789 ET patients and 770 healthy individuals to investigate whether there was an enrichment of rare deleterious variants within our candidate genes. RESULTS: Fifteen variants co-segregated with disease status in at least one of the families, among which rs749875462 in CCDC183, rs535864157 in MMP10 and rs114285050 in GPR151 showed a nominal association with ET. However, we found no significant enrichment of rare variants within these genes in cases compared with controls. Interestingly, MMP10 protein is involved in the inflammatory response to neuronal damage and has been previously associated with other neurological disorders. CONCLUSIONS: We prioritized a set of promising genes, especially MMP10, for further genetic and functional studies in ET. Our study suggests that rare deleterious coding variants that markedly increase susceptibility to ET are likely to be found in many genes. Future studies are needed to replicate and further infer biological mechanisms and potential disease causality for our identified genes.

Left-hemispheric predominance of nigrostriatal deficit in isolated REM sleep behavior disorder.

OBJECTIVE: Unilateral onset of parkinsonism due to nigrostriatal damage of the contralateral hemisphere is frequent in Parkinson disease (PD). There is evidence for a left-hemispheric bias of motor asymmetry in right-handed patients with PD indicating a hemispheric dominance. Isolated REM sleep behavior disorder (IRBD) constitutes the prodromal stage of PD and other synucleinopathies. To test the hypothesis that right-handed patients with IRBD exhibit left-hemispheric predominance of subclinical nigrostriatal dysfunction, we evaluated this aspect using neuroimaging instruments. METHODS: In 167 right-handed patients with IRBD without parkinsonism, we evaluated in each hemisphere the integrity of the striatal dopaminergic terminals by dopamine transporter (DAT)-SPECT and the substantia nigra echogenicity by transcranial sonography. RESULTS: DAT-SPECT showed lower specific binding ratio (SBR) in the left striatum and left caudate nucleus than in the right striatum and right caudate nucleus. The percentage of patients with lower SBR was greater in the left striatum and left caudate nucleus than in the right striatum and right caudate nucleus. In those who developed a synucleinopathy in <5 years from DAT-SPECT, there was a lower SBR in the left putamen and left caudate nucleus than in the right putamen and right caudate nucleus. Substantia nigra echogenic size was greater in the left than in the right side in patients with hyperechogenicity and among individuals who phenoconverted in <5 years from transcranial sonography. CONCLUSION: Right-handed patients with IRBD exhibit left-hemispheric predominance of subclinical nigrostriatal dysfunction. In premotor PD, the neurodegenerative process begins asymmetrically, initially impairing the nigrostriatal system of the dominant hemisphere.

Olfaction in LRRK2 Linked Parkinson's Disease: Is It Different from Idiopathic Parkinson's Disease?

BACKGROUND: Studies on olfaction in LRRK2-associated Parkinson's disease (LRRK2-PD) have yielded variable results. The impact of smell dysfunction upon daily life activities have been rarely assessed in PD. OBJECTIVE: To characterize the olfactory deficit in LRRK2-PD and its impact on daily life activities. METHODS: Twenty-four LRRK2-PD, 40 idiopathic PD (IPD), and 49 age-sex-matched controls were interviewed about olfactory characteristics and the impact of smell on daily life activities. The Barcelona Smell Identification test (BAST-24) and the Spanish-version of the 40-item University of Pennsylvania smell test (UPSIT) were applied. RESULTS: Nineteen (79.2%) LRRK2-PD patients reported subjective smell impairment with a low impact upon daily living activities. UPSIT score was higher in LRRK2-PD than in IPD (22.54±7.98 vs 18.84±6.03; p = 0.042). All IPD and 95.8% LRRK2-PD patients had hyposmia/anosmia, assessed by means of the UPSIT. No differences were found between LRRK2-PD and IPD regarding smell detection, memory or forced-choice identification. CONCLUSION: Most LRRK2-PD patients reported subjective smell impairment and presented hyposmia, according to validated smell tests, with a low impact of the smell dysfunction on daily life activities.