LRRK2 Inhibition by BIIB122 in Healthy Participants and Patients with Parkinson's Disease.

BACKGROUND: Leucine-rich repeat kinase 2 (LRRK2) inhibition is a promising therapeutic approach for the treatment of Parkinson's disease (PD). OBJECTIVE: The aim of this study was to evaluate the safety, tolerability, pharmacokinetics, and pharmacodynamics of the potent, selective, CNS-penetrant LRRK2 inhibitor BIIB122 (DNL151) in healthy participants and patients with PD. METHODS: Two randomized, double-blind, placebo-controlled studies were completed. The phase 1 study (DNLI-C-0001) evaluated single and multiple doses of BIIB122 for up to 28 days in healthy participants. The phase 1b study (DNLI-C-0003) evaluated BIIB122 for 28 days in patients with mild to moderate PD. The primary objectives were to investigate the safety, tolerability, and plasma pharmacokinetics of BIIB122. Pharmacodynamic outcomes included peripheral and central target inhibition and lysosomal pathway engagement biomarkers. RESULTS: A total of 186/184 healthy participants (146/145 BIIB122, 40/39 placebo) and 36/36 patients (26/26 BIIB122, 10/10 placebo) were randomized/treated in the phase 1 and phase 1b studies, respectively. In both studies, BIIB122 was generally well tolerated; no serious adverse events were reported, and the majority of treatment-emergent adverse events were mild. BIIB122 cerebrospinal fluid/unbound plasma concentration ratio was ~1 (range, 0.7-1.8). Dose-dependent median reductions from baseline were observed in whole-blood phosphorylated serine 935 LRRK2 (≤98%), peripheral blood mononuclear cell phosphorylated threonine 73 pRab10 (≤93%), cerebrospinal fluid total LRRK2 (≤50%), and urine bis (monoacylglycerol) phosphate (≤74%). CONCLUSIONS: At generally safe and well-tolerated doses, BIIB122 achieved substantial peripheral LRRK2 kinase inhibition and modulation of lysosomal pathways downstream of LRRK2, with evidence of CNS distribution and target inhibition. These studies support continued investigation of LRRK2 inhibition with BIIB122 for the treatment of PD. © 2023 Denali Therapeutics Inc and The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Cerebral Expression of Metabotropic Glutamate Receptor Subtype 5 in Idiopathic Autism Spectrum Disorder and Fragile X Syndrome: A Pilot Study.

Multiple lines of evidence suggest that dysfunction of the metabotropic glutamate receptor subtype 5 (mGluR5) plays a role in the pathogenesis of autism spectrum disorder (ASD). Yet animal and human investigations of mGluR5 expression provide conflicting findings about the nature of dysregulation of cerebral mGluR5 pathways in subtypes of ASD. The demonstration of reduced mGluR5 expression throughout the living brains of men with fragile X syndrome (FXS), the most common known single-gene cause of ASD, provides a clue to examine mGluR5 expression in ASD. We aimed to (A) compare and contrast mGluR5 expression in idiopathic autism spectrum disorder (IASD), FXS, and typical development (TD) and (B) show the value of positron emission tomography (PET) for the application of precision medicine for the diagnosis and treatment of individuals with IASD, FXS, and related conditions. Two teams of investigators independently administered 3-[18F]fluoro-5-(2-pyridinylethynyl)benzonitrile ([18F]FPEB), a novel, specific mGluR5 PET ligand to quantitatively measure the density and the distribution of mGluR5s in the brain regions, to participants of both sexes with IASD and TD and men with FXS. In contrast to participants with TD, mGluR5 expression was significantly increased in the cortical regions of participants with IASD and significantly reduced in all regions of men with FXS. These results suggest the feasibility of this protocol as a valuable tool to measure mGluR5 expression in clinical trials of individuals with IASD and FXS and related conditions.

Clinical and Imaging Progression in the PARS Cohort: Long-Term Follow-up.

BACKGROUND AND OBJECTIVES: The PARS (Parkinson Associated Risk Syndrome) study was designed to test whether screening for hyposmia followed by dopamine transporter imaging can identify risk for conversion to clinical PD, and to evaluate progression markers during the prodromal period. METHODS: Subjects with hyposmia completed annual clinical evaluations and biennial [123 I]ß-CIT single-photon emission computed tomography scans. Subjects were categorized as normal (>80% age-expected tracer uptake; n = 134), indeterminate (>65-80%; n = 30), and dopamine transporter deficit (≤65%; n = 21) by their baseline scan, and survival analysis was used to compare risk of conversion to motor PD. Progressing to a scan with a dopamine transporter deficit was assessed for those subjects with either normal or indeterminate baseline imaging. RESULTS: Over a mean of 6.3 [standard deviation: 2.2] years of follow-up, 67% (n = 14) of dopamine transporter deficit subjects, 20% (n = 6) of dopamine transporter indeterminate subjects, and 4% (n = 6) of dopamine transporter normal subjects converted to a PD diagnosis (P < 0.0001). Among subjects without dopamine transporter deficit at baseline, a reduction to ≤65% age-expected uptake occurred in 12 of 30 (40%) with indeterminate dopamine transporter and 7 of 134 (5%) with no dopamine transporter DAT deficit (P < 0.0001). Imaging conversion during follow-up was associated with subsequent clinical conversion (hazard ratio: 9.6; P = 0.0157). DISCUSSION AND CONCLUSIONS: Long-term follow-up of the PARS cohort demonstrated a high rate of conversion to clinical PD in subjects who either had abnormal dopamine transporter imaging at baseline or developed abnormal imaging during follow-up. These data extend the earlier PARS findings and present new results showing the sequence of incident imaging deficit, imaging progression, and clinical changes that occur in prodromal PD. © 2020 International Parkinson and Movement Disorder Society.

Plasma α-synuclein and cognitive impairment in the Parkinson's Associated Risk Syndrome: A pilot study.

Plasma total and nervous system derived exosomal (NDE) α-synuclein have been determined as potential biomarkers of Parkinson's disease (PD). To explore the utility of plasma α-synuclein in the prodromal phase of PD, plasma total and NDE α-synuclein were evaluated in baseline and 2-year follow-up samples from 256 individuals recruited as part of the Parkinson's Associated Risk Syndrome (PARS) study. The results demonstrated that baseline and longitudinal increases in total α-synuclein predicted progression of cognitive decline in hyposmic individuals with dopamine transporter (DAT) binding reduction. On the other hand, a longitudinal decrease in NDE α-synuclein predicted worsening cognitive scores in hyposmic individuals with DAT binding reduction. Finally, in individuals with faster DAT progression, decreasing NDE/total α-synuclein ratio was associated with a larger reduction in DAT from baseline to follow-up. These results suggest that, though underlying mechanisms remain to be defined, alterations in plasma total and NDE α-synuclein concentrations are likely associated with PD progression, especially in the aspect of cognitive impairment, at early stages of the disease.

Baseline prevalence and longitudinal evolution of non-motor symptoms in early Parkinson's disease: the PPMI cohort.

OBJECTIVE: To examine the baseline prevalence and longitudinal evolution in non-motor symptoms (NMS) in a prospective cohort of, at baseline, patients with de novo Parkinson's disease (PD) compared with healthy controls (HC). METHODS: Parkinson's Progression Markers Initiative (PPMI) is a longitudinal, ongoing, controlled study of de novo PD participants and HC. NMS were rated using the Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS) Part I score and other validated NMS scales at baseline and after 2 years. Biological variables included cerebrospinal fluid (CSF) markers and dopamine transporter imaging. RESULTS: 423 PD subjects and 196 HC were enrolled and followed for 2 years. MDS-UPDRS Part I total mean (SD) scores increased from baseline 5.6 (4.1) to 7.7 (5.0) at year 2 in PD subjects (p<0.001) versus from 2.9 (3.0) to 3.2 (3.0) in HC (p=0.38), with a significant difference between the groups (p<0.001). In the multivariate analysis, higher baseline NMS score was associated with female sex (p=0.008), higher baseline MDS-UPDRS Part II scores (p<0.001) and more severe motor phenotype (p=0.007). Longitudinal increase in NMS severity was associated with the older age (0.008) and lower CSF Aß1-42 (0.005) at baseline. There was no association with the dose or class of dopaminergic therapy. CONCLUSIONS: This study of NMS in early PD identified clinical and biological variables associated with both baseline burden and predictors of progression. The association of a greater longitudinal increase in NMS with lower baseline Aß1-42 level is an important finding that will have to be replicated in other cohorts. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT01141023.

Longitudinal Change of Clinical and Biological Measures in Early Parkinson's Disease: Parkinson's Progression Markers Initiative Cohort.

OBJECTIVE: The objective of this study was to assess longitudinal change in clinical and dopamine transporter imaging outcomes in early, untreated PD. METHODS: We describe 5-year longitudinal change of the MDS-UPDRS and other clinical measures using results from the Parkinson's Progression Markers Initiative, a longitudinal cohort study of early Parkinson's disease (PD) participants untreated at baseline. We also provide data on the longitudinal change in dopamine transporter 123-I Ioflupane striatal binding and correlation between the 2 measures. RESULTS: A total of 423 PD participants were recruited, and 358 remain in the study at year 5. Baseline MDS-UPDRS total score was 32.4 (standard deviation 13.1), and the average annual change (assessed medications OFF for the treated participants) was 7.45 (11.6), 3.11 (11.7), 4(11.9), 4.7 (11.1), and 1.74(11.9) for years 1, 2, 3, 4, and 5, respectively (P < .0001 for the change over time), with a steeper change in year 1. Dopaminergic therapy had a significant effect on the change of MDS-UPDRS. There was a significant longitudinal change in dopamine transporter binding in all striatal regions (P < .001). There was a significant but weak correlation between MDS-UPDRS and dopamine transporter binding at baseline and years 1, 2, and 4, but no correlation between the rate of change of the 2 variables. CONCLUSIONS: We present 5-year longitudinal data on the change of the MDS-UPDRS and other clinical and dopamine transporter imaging outcome measures in early PD. These data can be used for sample size estimates for interventional studies in the de novo PD population. © 2018 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Relationships between flortaucipir PET tau binding and amyloid burden, clinical diagnosis, age and cognition.

The advent of tau-targeted positron emission tomography tracers such as flortaucipir (18F-AV-1451, also known as 18F-T807) have made it possible to investigate the sequence of development of tau and amyloid-ß in relationship to age, and to the development of cognitive impairment due to Alzheimer's disease. In this study, flortaucipir tau and florbetapir amyloid positron emission tomography were obtained for 217 subjects including 16 young and 58 older cognitively normal subjects, 95 subjects with mild cognitive impairment (Mini-Mental State Examination 24-30) and 48 subjects with clinically-defined possible or probable Alzheimer's disease (Mini-Mental State Examination >10). Images were evaluated visually and quantitatively by regional and voxel-based cortical to cerebellar standard uptake value ratios. For amyloid positron emission tomography positive (Aß+) subjects, flortaucipir neocortical standard uptake value ratio was significantly higher with more advanced clinical stage (Alzheimer's disease > mild cognitive impairment > older cognitively normal) and was significantly elevated for Aß+ mild cognitive impairment and Alzheimer's disease subjects relative to the respective Aß- subjects. In contrast, florbetapir Aß- older cognitively normal subjects showed an increase in flortaucipir standard uptake value ratios in mesial temporal lobe regions (amygdala, hippocampus/choroid plexus region of interest) compared to younger cognitively normal subjects, but no increased standard uptake value ratios in neocortical regions. Analysis of covariance with planned contrasts showed no differences in regional or composite posterior neocortical flortaucipir standard uptake value ratio as a function of diagnostic group among Aß- older cognitively normal or clinically diagnosed Alzheimer's disease or mild cognitive impairment subjects. The pattern of flortaucipir distribution among Aß+ subjects was reminiscent of the cross-sectional distribution of tau reported in post-mortem pathology studies, in that the most commonly affected regions were the inferior and lateral temporal lobes, the same regions where the first signs of increased retention appeared in Aß+ cognitively normal subjects. However, there was large variability in extent/density of flortaucipir tau binding among Aß+ subjects. Although high neocortical flortaucipir retention was consistently associated with an Aß+ florbetapir positron emission tomography scan, not all Aß+ subjects had elevated flortaucipir standard uptake value ratios. Finally, within the Aß+ group, increasing levels of flortaucipir tau binding were associated with increased cognitive impairment, as assessed by Mini-Mental State Examination and Alzheimer's Disease Assessment Scale. These results suggest development of tau beyond the mesial temporal lobe is associated with, and may be dependent on, amyloid accumulation. Further, the results are consistent with the hypothesis that cortical tau is associated with cognitive impairment.

Vitamin D in the Parkinson Associated Risk Syndrome (PARS) study.

BACKGROUND: Lower vitamin D levels have been associated with manifest Parkinson's disease, prompting the hypothesis that vitamin D insufficiency or deficiency may increase risk for PD. OBJECTIVES: To evaluate vitamin D levels in a population at risk for developing PD. METHODS: Plasma vitamin D levels were measured in the Parkinson Associated Risk Syndrome Study, a cohort of asymptomatic individuals, some of whom are at high risk for PD. Vitamin D levels were compared between subjects at high risk for PD (hyposmia and dopamine transporter scan deficit) versus all others and examined for correlations with dopaminergic system integrity. RESULTS: Mean vitamin D levels did not differ between groups, with a level of 27.8 ng/mL (standard deviation = 12.0) in the high-risk group versus 24.7 ng/mL (standard deviation = 9.0) in all others (P = 0.09). Vitamin D levels did not associate with putaminal dopamine transporter uptake. CONCLUSIONS: Our data from the asymptomatic Parkinson Associated Risk Syndrome cohort do not support the hypothesis that chronic vitamin D insufficiency threatens dopaminergic system integrity, contributing to PD pathogenesis. © 2017 International Parkinson and Movement Disorder Society.

Cognition and the course of prodromal Parkinson's disease.

BACKGROUND: Prospective data on cognition in prodromal Parkinson's disease are limited. The objectives of this study were to assess in prodromal PD (1) if baseline cognition predicts conversion to clinical PD, (2) if baseline dopamine transporter binding predicts longitudinal changes in cognition, and (3) if impaired olfaction predicts future cognitive decline. METHODS: Prodromal participants were 136 hyposmic individuals enrolled in the Parkinson Associated Risk Study. We examined baseline neuropsychological test performance in PD converters versus nonconverters and the association between baseline dopamine transporter binding and change in cognition. An additional 73 normosmic individuals were included in analyses of the relationship between hyposmia and cognitive decline. RESULTS: In prodromal participants, baseline cognitive scores did not significantly predict conversion, but converters performed numerically worse on 5 of the 6 cognitive domains assessed, with the greatest differences in executive function/working memory (0.68 standard deviation lower) and global cognition (0.64 standard deviation lower). Lower baseline dopamine transporter binding predicted greater future decline in processing speed/attention (P = 0.02). Hyposmia predicted greater future decline in language (P = 0.005) and memory (P = 0.01) abilities. CONCLUSIONS: Given hyposmia in the general population predicts cognitive decline, the role of cognition in predicting conversion in prodromal PD needs to be assessed in large cohorts followed long-term. The dopamine system may be associated with changes in processing speed/attention in individuals at risk for PD. © 2017 International Parkinson and Movement Disorder Society.

Preclinical properties and human in vivo assessment of 123I-ABC577 as a novel SPECT agent for imaging amyloid-ß.

Non-invasive imaging of amyloid-ß in the brain, a hallmark of Alzheimer's disease, may support earlier and more accurate diagnosis of the disease. In this study, we assessed the novel single photon emission computed tomography tracer (123)I-ABC577 as a potential imaging biomarker for amyloid-ß in the brain. The radio-iodinated imidazopyridine derivative (123)I-ABC577 was designed as a candidate for a novel amyloid-ß imaging agent. The binding affinity of (123)I-ABC577 for amyloid-ß was evaluated by saturation binding assay and in vitro autoradiography using post-mortem Alzheimer's disease brain tissue. Biodistribution experiments using normal rats were performed to evaluate the biokinetics of (123)I-ABC577. Furthermore, to validate (123)I-ABC577 as a biomarker for Alzheimer's disease, we performed a clinical study to compare the brain uptake of (123)I-ABC577 in three patients with Alzheimer's disease and three healthy control subjects. (123)I-ABC577 binding was quantified by use of the standardized uptake value ratio, which was calculated for the cortex using the cerebellum as a reference region. Standardized uptake value ratio images were visually scored as positive or negative. As a result, (123)I-ABC577 showed high binding affinity for amyloid-ß and desirable pharmacokinetics in the preclinical studies. In the clinical study, (123)I-ABC577 was an effective marker for discriminating patients with Alzheimer's disease from healthy control subjects based on visual images or the ratio of cortical-to-cerebellar binding. In patients with Alzheimer's disease, (123)I-ABC577 demonstrated clear retention in cortical regions known to accumulate amyloid, such as the frontal cortex, temporal cortex, and posterior cingulate. In contrast, less, more diffuse, and non-specific uptake without localization to these key regions was observed in healthy controls. At 150 min after injection, the cortical standardized uptake value ratio increased by ∼ 60% in patients with Alzheimer's disease relative to healthy control subjects. Both healthy control subjects and patients with Alzheimer's disease showed minimal (123)I-ABC577 retention in the white matter. These observations indicate that (123)I-ABC577 may be a useful single photon emission computed tomography imaging maker to identify amyloid-ß in the human brain. The availability of an amyloid-ß tracer for single photon emission computed tomography might increase the accessibility of diagnostic imaging for Alzheimer's disease.

CSF biomarkers associated with disease heterogeneity in early Parkinson's disease: the Parkinson's Progression Markers Initiative study.

The development of biomarkers to predict the progression of Parkinson's disease (PD) from its earliest stage through its heterogeneous course is critical for research and therapeutic development. The Parkinson's Progression Markers Initiative (PPMI) study is an ongoing international multicenter, prospective study to validate biomarkers in drug-naïve PD patients and matched healthy controls (HC). We quantified cerebrospinal fluid (CSF) alpha-synuclein (α-syn), amyloid-beta1-42 (Aß1-42), total tau (t-tau), and tau phosphorylated at Thr181 (p-tau) in 660 PPMI subjects at baseline, and correlated these data with measures of the clinical features of these subjects. We found that CSF α-syn, t-tau and p-tau levels, but not Aß1-42, were significantly lower in PD compared with HC, while the diagnostic value of the individual CSF biomarkers for PD diagnosis was limited due to large overlap. The level of α-syn, but not other biomarkers, was significantly lower in PD patients with non-tremor-dominant phenotype compared with tremor-dominant phenotype. In addition, in PD patients the lowest Aß1-42, or highest t-tau/Aß1-42 and t-tau/α-syn quintile in PD patients were associated with more severe non-motor dysfunction compared with the highest or lowest quintiles, respectively. In a multivariate regression model, lower α-syn was significantly associated with worse cognitive test performance. APOE ε4 genotype was associated with lower levels of Aß1-42, but neither with PD diagnosis nor cognition. Our data suggest that the measurement of CSF biomarkers in early-stage PD patients may relate to disease heterogeneity seen in PD. Longitudinal observations in PPMI subjects are needed to define their prognostic performance.

Cognition in individuals at risk for Parkinson's: Parkinson associated risk syndrome (PARS) study findings.

OBJECTIVES: The Parkinson Associated Risk Syndrome Study identified a cohort of healthy adults with hyposmia and dopamine transporter binding reduction to characterize individuals at risk for Parkinson's disease (PD). We describe the cognitive profile of this cohort. METHODS: Individuals older than 50 y without PD were recruited. Two hundred twenty-five completed cognitive testing and were included in the final analysis. A neuropsychological test battery was administered and normative scores created for global cognition, memory, executive function/working memory, processing speed/attention, visuospatial abilities, and language domains. Other non-motor symptoms (constipation, depression, anxiety, and rapid eye movement sleep behavior disorder) were assessed through questionnaires. RESULTS: Individuals with both hyposmia and reduced dopamine transporter binding (n = 38) had lower mean scores for global cognition, executive function/working memory, and memory compared with all other participants (n = 187). In separate multivariate logistic regression models, lower global cognition (odds ratio, 1.97, P = 0.004), and specifically executive function/working memory (odds ratio, 1.84, P = 0.004) scores were associated with membership in the hyposmia with dopamine transporter reduction group. Combining hyposmia with relative impairment on specific cognitive domains increased the odds of dopamine transporter binding reduction compared with hyposmia alone, with the greatest increase in odds for hyposmia plus executive function/working memory relative impairment (68% increase in odds from 4.14 to 6.96). CONCLUSION: Changes in global cognitive abilities, and specifically executive function/working memory, are present in individuals at risk for PD. Combining non-motor features, including cognition, improves prediction of dopamine transporter binding reduction.

Plasma apolipoprotein A1 as a biomarker for Parkinson disease.

OBJECTIVE: To identify plasma-based biomarkers for Parkinson disease (PD) risk. METHODS: In a discovery cohort of 152 PD patients, plasma levels of 96 proteins were measured by multiplex immunoassay; proteins associated with age at PD onset were identified by linear regression. Findings from discovery screening were then assessed in a second cohort of 187 PD patients, using a different technique. Finally, in a third cohort of at-risk, asymptomatic individuals enrolled in the Parkinson's Associated Risk Study (PARS, n = 134), plasma levels of the top candidate biomarker were measured, and dopamine transporter (DAT) imaging was performed, to evaluate the association of plasma protein levels with dopaminergic system integrity. RESULTS: One of the best candidate protein biomarkers to emerge from discovery screening was apolipoprotein A1 (ApoA1; p = 0.001). Low levels of ApoA1 correlated with earlier PD onset, with a 26% decrease in risk of developing PD associated with each tertile increase in ApoA1 (Cox proportional hazards, p < 0.001, hazard ratio = 0.742). The association between plasma ApoA1 levels and age at PD onset was replicated in an independent cohort of PD patients (p < 0.001). Finally, in the PARS cohort of high-risk, asymptomatic subjects, lower plasma levels of ApoA1 were associated with greater putaminal DAT deficit (p = 0.037). INTERPRETATION: Lower ApoA1 levels correlate with dopaminergic system vulnerability in symptomatic PD patients and in asymptomatic individuals with physiological reductions in dopamine transporter density consistent with prodromal PD. Plasma ApoA1 may be a new biomarker for PD risk.

A biological definition of neuronal α-synuclein disease: towards an integrated staging system for research.

Parkinson's disease and dementia with Lewy bodies are currently defined by their clinical features, with α-synuclein pathology as the gold standard to establish the definitive diagnosis. We propose that, given biomarker advances enabling accurate detection of pathological α-synuclein (ie, misfolded and aggregated) in CSF using the seed amplification assay, it is time to redefine Parkinson's disease and dementia with Lewy bodies as neuronal α-synuclein disease rather than as clinical syndromes. This major shift from a clinical to a biological definition of Parkinson's disease and dementia with Lewy bodies takes advantage of the availability of tools to assess the gold standard for diagnosis of neuronal α-synuclein (n-αsyn) in human beings during life. Neuronal α-synuclein disease is defined by the presence of pathological n-αsyn species detected in vivo (S; the first biological anchor) regardless of the presence of any specific clinical syndrome. On the basis of this definition, we propose that individuals with pathological n-αsyn aggregates are at risk for dopaminergic neuronal dysfunction (D; the second biological anchor). Our biological definition establishes a staging system, the neuronal α-synuclein disease integrated staging system (NSD-ISS), rooted in the biological anchors (S and D) and the degree of functional impairment caused by clinical signs or symptoms. Stages 0-1 occur without signs or symptoms and are defined by the presence of pathogenic variants in the SNCA gene (stage 0), S alone (stage 1A), or S and D (stage 1B). The presence of clinical manifestations marks the transition to stage 2 and beyond. Stage 2 is characterised by subtle signs or symptoms but without functional impairment. Stages 2B-6 require both S and D and stage-specific increases in functional impairment. A biological definition of neuronal α-synuclein disease and an NSD-ISS research framework are essential to enable interventional trials at early disease stages. The NSD-ISS will evolve to include the incorporation of data-driven definitions of stage-specific functional anchors and additional biomarkers as they emerge and are validated. Presently, the NSD-ISS is intended for research use only; its application in the clinical setting is premature and inappropriate.

Predictive value of abbreviated olfactory tests in prodromal Parkinson disease.

There is disagreement in the literature whether olfaction may show specific impairments in Parkinson Disease (PD) and if olfactory tests comprised of selected odors could be more specific for diagnosis. We sought to validate previously proposed subsets of the University of Pennsylvania Smell Identification Test (UPSIT) odors for predicting conversion to PD in an independent, prodromal cohort. Conversion to PD was assessed in 229 participants in the Parkinson At Risk Study who completed baseline olfactory testing with the UPSIT and up to 12 years of clinical and imaging evaluations. No commercially available or proposed subset performed better than the full 40-item UPSIT. The proposed "PD-specific" subsets also did not perform better than expected by chance. We did not find evidence for selective olfactory impairment in Parkinson disease. Shorter odor identification tests, including commercially available 10-12 item tests, may have utility for ease of use and cost, but not for superior predictive value.

Clinical Characterization of [18F]T-008, a Cholesterol 24-Hydroxylase PET Ligand: Dosimetry, Kinetic Modeling, Variability, and Soticlestat Occupancy.

This series of studies characterized [18F]T-008, a PET radiotracer for imaging cholesterol 24-hydroxylase (CH24H), in healthy volunteers (ClinicalTrials.gov identifier NCT02497235). Assessments included radiation dosimetry, kinetic modeling, test-retest variability (TRT) evaluation, and a dose occupancy evaluation using soticlestat, a selective CH24H inhibitor. Soticlestat is currently in phase 3 development for the treatment of seizures in Dravet syndrome and Lennox-Gastaut syndrome. Methods: In the dosimetry study, 5 participants (3 men) underwent serial whole-body scans to estimate organ-absorbed doses and effective doses of [18F]T-008 using OLINDA/EXM 1.1. For the kinetic modeling and TRT study, 6 participants (all men) underwent two 210-min dynamic [18F]T-008 PET scans with arterial blood sampling. The regional total volume of distribution was estimated using a 1-tissue-compartment model, a 2-tissue-compartment model, and Logan graphic analysis. In the dose occupancy study, 11 participants (all men) underwent 120-min scans at baseline and 2 time points (peak and trough) after receiving single oral doses of soticlestat (50-600 mg). The relationship between effect-site soticlestat concentration and brain occupancy was evaluated with a specially developed pharmacokinetic model and a saturable maximal occupancy model. Results: The estimated mean whole-body effective dose was 0.0292 mSv/MBq (SD, 0.00147 mSv/MBq). [18F]T-008 entered the brain rapidly, with a distribution consistent with known CH24H distribution densities. The 2-tissue-compartment model and Logan graphic analysis best described the tracer kinetics. The mean TRT for estimating total volume of distribution was 7%-15%. Single doses of soticlestat in the range 50-600 mg resulted in occupancies of 64%-96% at 2 h and 11%-79% at 24 h. The estimated half-maximal effect-site concentration of soticlestat was 5.52 ng/mL. Conclusion: [18F]T-008 is a suitable PET radiotracer for quantitatively analyzing CH24H in the human brain. Using [18F]T-008 and PET, we demonstrated that soticlestat was brain-penetrant and established target engagement by displacing [18F]T-008 in a dose-dependent manner in the brain.

Impaired olfaction and other prodromal features in the Parkinson At-Risk Syndrome Study.

To test the association between impaired olfaction and other prodromal features of PD in the Parkinson At-Risk Syndrome Study. The onset of olfactory dysfunction in PD typically precedes motor features, suggesting that olfactory testing could be used as a screening test. A combined strategy that uses other prodromal nonmotor features, along with olfactory testing, may be more efficient than hyposmia alone for detecting the risk of PD. Individuals with no neurological diagnosis completed a mail survey, including the 40-item University of Pennsylvania Smell Identification Test, and questions on prodromal features of PD. The frequency of reported nonmotor features was compared across individuals with and without hyposmia. A total of 4,999 subjects completed and returned the survey and smell test. Of these, 669 were at or below the 15th percentile based on age and gender, indicating hyposmia. Hyposmics were significantly more likely to endorse nonmotor features, including anxiety and depression, constipation, and rapid eye movement sleep behavior disorder symptoms, and to report changes in motor function. Twenty-six percent of subjects with combinations of four or more nonmotor features were hyposmic, compared to 12% for those reporting three or fewer nonmotor features (P < 0.0001). Hyposmia is associated with other nonmotor features of PD in undiagnosed individuals. Further assessment of hyposmic subjects using more specific markers for degeneration, such as dopamine transporter imaging, will evaluate whether combining hyposmia and other nonmotor features is useful in assessing the risk of future neurodegeneration.

Serial olfactory testing for the diagnosis of prodromal Parkinson's disease in the PARS study.

BACKGROUND: The Parkinson Associated Risk Syndrome (PARS) study was designed to evaluate whether screening with olfactory testing and dopamine transporter (DAT) imaging could identify participants at risk for developing Parkinson's disease (PD). OBJECTIVE: Hyposmia on a single test has been associated with increased risk of PD, but, taken alone, lacks specificity. We evaluated whether repeating olfactory testing improves the diagnostic characteristics of this screening approach. METHODS: Participants completed up to 10 years of clinical and imaging evaluations in the PARS cohort. Olfaction was assessed with the University of Pennsylvania Smell Identification Test at baseline and on average 1.4 years later. Multiple logistic regression and Cox proportional hazards regression were used to estimate the hazard of development of clinical PD or abnormal DAT imaging. RESULTS: Of 186 participants who were initially hyposmic, 28% reverted to normosmia on repeat testing (reverters). No initially normosmic subjects and only 2% of reverters developed DAT imaging progression or clinical PD, compared to 29% of subjects with persistent hyposmia who developed abnormal DAT and 20% who developed clinical PD. The relative risk of clinical conversion to PD was 8.3 (95% CI:0.92-75.2, p = 0.06) and of abnormal DAT scan was 12.5 (2.4-156.2, p = 0.005) for persistent hyposmia, compared to reversion. CONCLUSIONS: Persistent hyposmia on serial olfactory testing significantly increases the risk of developing clinical PD and abnormal DAT imaging, compared to hyposmia on a single test. Repeat olfactory testing may be an efficient and cost-effective strategy to improve identification of at-risk patients for early diagnosis and disease modification studies.

Fragile X Mental Retardation Protein and Cerebral Expression of Metabotropic Glutamate Receptor Subtype 5 in Men with Fragile X Syndrome: A Pilot Study.

Multiple lines of evidence suggest that a deficiency of Fragile X Mental Retardation Protein (FMRP) mediates dysfunction of the metabotropic glutamate receptor subtype 5 (mGluR5) in the pathogenesis of fragile X syndrome (FXS), the most commonly known single-gene cause of inherited intellectual disability (ID) and autism spectrum disorder (ASD). Nevertheless, animal and human studies regarding the link between FMRP and mGluR5 expression provide inconsistent or conflicting findings about the nature of those relationships. Since multiple clinical trials of glutamatergic agents in humans with FXS did not demonstrate the amelioration of the behavioral phenotype observed in animal models of FXS, we sought measure if mGluR5 expression is increased in men with FXS to form the basis for improved clinical trials. Unexpectedly marked reductions in mGluR5 expression were observed in cortical and subcortical regions in men with FXS. Reduced mGluR5 expression throughout the living brains of men with FXS provides a clue to examine FMRP and mGluR5 expression in FXS. In order to develop the findings of our previous study and to strengthen the objective tools for future clinical trials of glutamatergic agents in FXS, we sought to assess the possible value of measuring both FMRP levels and mGluR5 expression in men with FXS. We aimed to show the value of measurement of FMRP levels and mGluR5 expression for the diagnosis and treatment of individuals with FXS and related conditions. We administered 3-[18F]fluoro-5-(2-pyridinylethynyl)benzonitrile ([18F]FPEB), a specific mGluR5 radioligand for quantitative measurements of the density and the distribution of mGluR5s, to six men with the full mutation (FM) of FXS and to one man with allele size mosaicism for FXS (FXS-M). Utilizing the seven cortical and subcortical regions affected in neurodegenerative disorders as indicator variables, adjusted linear regression of mGluR5 expression and FMRP showed that mGluR5 expression was significantly reduced in the occipital cortex and the thalamus relative to baseline (anterior cingulate cortex) if FMRP levels are held constant (F(7,47) = 6.84, p < 0.001).These findings indicate the usefulness of cerebral mGluR5 expression measured by PET with [18F]FPEB and FMRP values in men with FXS and related conditions for assessments in community facilities within a hundred-mile radius of a production center with a cyclotron. These initial results of this pilot study advance our previous study regarding the measurement of mGluR5 expression by combining both FMRP levels and mGluR5 expression as tools for meaningful clinical trials of glutamatergic agents for men with FXS. We confirm the feasibility of this protocol as a valuable tool to measure FMRP levels and mGluR5 expression in clinical trials of individuals with FXS and related conditions and to provide the foundations to apply precision medicine to tailor treatment plans to the specific needs of individuals with FXS and related conditions.

Preclinical and clinical evaluation of the LRRK2 inhibitor DNL201 for Parkinson's disease.

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common genetic risk factors for Parkinson's disease (PD). Increased LRRK2 kinase activity is thought to impair lysosomal function and may contribute to the pathogenesis of PD. Thus, inhibition of LRRK2 is a potential disease-modifying therapeutic strategy for PD. DNL201 is an investigational, first-in-class, CNS-penetrant, selective, ATP-competitive, small-molecule LRRK2 kinase inhibitor. In preclinical models, DNL201 inhibited LRRK2 kinase activity as evidenced by reduced phosphorylation of both LRRK2 at serine-935 (pS935) and Rab10 at threonine-73 (pT73), a direct substrate of LRRK2. Inhibition of LRRK2 by DNL201 demonstrated improved lysosomal function in cellular models of disease, including primary mouse astrocytes and fibroblasts from patients with Gaucher disease. Chronic administration of DNL201 to cynomolgus macaques at pharmacologically relevant doses was not associated with adverse findings. In phase 1 and phase 1b clinical trials in 122 healthy volunteers and in 28 patients with PD, respectively, DNL201 at single and multiple doses inhibited LRRK2 and was well tolerated at doses demonstrating LRRK2 pathway engagement and alteration of downstream lysosomal biomarkers. Robust cerebrospinal fluid penetration of DNL201 was observed in both healthy volunteers and patients with PD. These data support the hypothesis that LRRK2 inhibition has the potential to correct lysosomal dysfunction in patients with PD at doses that are generally safe and well tolerated, warranting further clinical development of LRRK2 inhibitors as a therapeutic modality for PD.