LRRK2 G2019S Parkinson's disease with more benign phenotype than idiopathic

Genetic analysis and natural history of Parkinson's disease due to the LRRK2 G2019S variant

The LRRK2 G2019S variant is the most common cause of monogenic Parkinson's disease (PD); however, questions remain regarding the penetrance, clinical phenotype and natural history of carriers. We performed a 3.5-year prospective longitudinal online study in a large number of 1286 genotyped LRRK2 G2019S carriers and 109 154 controls, with and without PD, recruited from the 23andMe Research Cohort. We collected self-reported motor and non-motor symptoms every 6 months, as well as demographics, family histories and environmental risk factors. Incident cases of PD (phenoconverters) were identified at follow-up. We determined lifetime risk of PD using accelerated failure time modelling and explored the impact of polygenic risk on penetrance. We also computed the genetic ancestry of all LRRK2 G2019S carriers in the 23andMe database and identified regions of the world where carrier frequencies are highest. We observed that despite a 1 year longer disease duration (P = 0.016), LRRK2 G2019S carriers with PD had similar burden of motor symptoms, yet significantly fewer non-motor symptoms including cognitive difficulties, REM sleep behaviour disorder (RBD) and hyposmia (all P-values ≤ 0.0002). The cumulative incidence of PD in G2019S carriers by age 80 was 49%. G2019S carriers had a 10-fold risk of developing PD versus non-carriers. This rose to a 27-fold risk in G2019S carriers with a PD polygenic risk score in the top 25% versus non-carriers in the bottom 25%. In addition to identifying ancient founding events in people of North African and Ashkenazi descent, our genetic ancestry analyses infer that the G2019S variant was later introduced to Spanish colonial territories in the Americas. Our results suggest LRRK2 G2019S PD appears to be a slowly progressive predominantly motor subtype of PD with a lower prevalence of hyposmia, RBD and cognitive impairment. This suggests that the current prodromal criteria, which are based on idiopathic PD, may lack sensitivity to detect the early phases of LRRK2 PD in G2019S carriers. We show that polygenic burden may contribute to the development of PD in the LRRK2 G2019S carrier population. Collectively, the results should help support screening programmes and candidate enrichment strategies for upcoming trials of LRRK2 inhibitors in early-stage disease.

Comprehensive analysis of clinical and biological features in Parkinson's disease associated with the LRRK2 G2019S mutation: Data from the PPMI study

The Parkinson's Progression Marker Initiative (PPMI) aims to identify biomarkers for Parkinson's disease (PD) risk, onset, and progression. This study focuses on the G2019S missense mutation in the LRRK2 gene, which is associated with hereditary and sporadic PD. Utilizing data from the PPMI database, we conducted an analysis of baseline clinical characteristics, as well as serum and cerebrospinal fluid levels in two groups: patients with PD with the G2019S mutation (PD + G2019S) and patients with PD without the mutation (PD-G2019S). Multiple linear regression and longitudinal analysis were performed, controlling for confounding factors. Compared to the PD-G2019S group, the PD + G2019S group showed more obvious initial motor dysfunction-higher baseline Movement Disorder Society-Sponsored Revision of the Unified Parkinson Disease Rating Scale (MDS-UPDRS) scores (false discovery rate [FDR]-adjusted p < 0.001), but progressed more slowly. Mechanism of Coordinated Access and activities of daily living (ADL) scores were lower at baseline (FDR-adjusted p < 0.001), whereas Scales for Outcomes of Parkinson's Disease (SCOPA)-Thermoregulatory (FDR-adjusted p = 0.015) scores were higher, emphasizing the increase of non-motor symptoms associated with LRRK2-G2019S mutation. During the follow-up period, the motor and non-motor symptoms changed dynamically with time, and there were longitudinal differences in the scores of MDS-UPDRS (FDR-adjusted PI  = 0.013, PII  = 0.008, PIV  < 0.001), Questionnaire for Impulsive-Compulsive Disorders in Parkinson's Disease (FDR-adjusted p = 0.027), SCOPA-Thermoregulatory (FDR-adjusted p = 0.021), and ADL (FDR-adjusted p = 0.027) scale scores. PD associated with the LRRK2 G2019S mutation demonstrated more severe symptoms at baseline but slower progression. Motor complications and thermoregulatory disorders were more pronounced.

Serum neurofilament light chain in LRRK2 related Parkinson's disease: A five years follow-up

BACKGROUND

Studies revealed that serum neurofilament light chain (NFL) levels not only increase considerably over time in Parkinson's disease (PD) but also have a significant association with disease progression. However, there is no evidence of the level of serum NFL in PD patients with leucine-rich repeat kinase 2 (LRRK2) mutation (LRRK2-PD) which is the most common mutation that causes familial and sporadic PD.

AIM

Here we aimed to investigate the difference and longitudinal alteration of the serum level of NFL in LRRK2-PD and idiopathic PD (iPD) patients.

METHODS

We entered 228 iPD and 103 LRRK2-PD patients and 176 healthy controls (HCs) from PPMI. We compared the level of serum NFL at baseline, six months, one year, two years, three years, and five years visits. Also, we used linear mixed models to assess longitudinal changes of serum NFL over six months, one year, two years, three years, and five years within groups.

RESULTS

We found a significant difference in the level of serum NFL between three groups at baseline, two years, three years, and five years time points. Also, our analysis showed that LRRK2-PD patients had significantly lower serum NFL compared to iPD subjects at baseline. In the longitudinal analysis, there was no significant change in the HCs group over five years. The level of serum NFL was significantly increased after two, three, and five years from baseline in LRRK2-PD patients. Also, we found similar results for iPD subjects after three and five years from baseline.

CONCLUSION

We can conclude that the overall neurodegeneration might be similar in LRRK2-PD and healthy subjects and lower than the idiopathic form of PD at the early stages, which may disappear in the later stages. Moreover, our findings suggest that the serum NFL might be a more accurate biomarker to distinguish iPD from healthy subjects rather than all PD patients or LRRK2-PD from healthy subjects at the early stages.

Cognitive deficits and altered cholinergic innervation in young adult male mice carrying a Parkinson's disease Lrrk2G2019S knockin mutation

Impaired executive function is a common and debilitating non-motor symptom of idiopathic and hereditary Parkinson's disease (PD), but there is little understanding of the underlying pathophysiological mechanisms and circuits. The G2019S mutation in the kinase domain of leucine-rich repeat kinase 2 (LRRK2) greatly increases risk for late-onset PD, and non-manifesting LRRK2^G2019S carriers can also exhibit early and significant cognitive impairment. Here, we subjected young adult male mice carrying a Lrrk2^G2019S knockin mutation to touchscreen-based operant tasks that measure attention, goal-directed learning and cognitive flexibility, all of which rely on frontal-striatal connectivity and are strongly modulated by cholinergic innervation. In a visuospatial attention task, mutant mice exhibited significantly more omissions and longer response latencies than controls that could not be attributed to deficits in motivation, visual sensory perception per se or locomotion, thereby suggesting impairments in divided attention and/or action-selection as well as generally slower information processing speed. Pretreating mice with the acetylcholinesterase inhibitor donepezil normalized both higher omission rates and longer response latencies in the mutants, but did not affect any performance metric in controls. Strikingly, cholinergic fiber density in cortical areas PL/IL and DMS (dorsomedial striatum) was significantly sparser in mutants than in controls, while further behavioral interrogation of the mutants revealed significant impairments in action-outcome associations but preserved cognitive flexibility. These data suggest that the Lrrk2^G2019S mutation negatively impacts cholinergic innervation anatomically and functionally by young adulthood, impairing corticostriatal network function in ways that may contribute to early PD-associated executive function deficits.

ERRγ Ligand Regulates Adult Neurogenesis and Depression-like Behavior in a LRRK2-G2019S-associated Young Female Mouse Model of Parkinson's Disease

Adult neurogenesis, a process controlling the proliferation to maturation of newly generated neurons in the post-developmental brain, is associated with various brain functions and pathogenesis of neuropsychological diseases, such as Parkinson's disease (PD) and depression. Because orphan nuclear receptor estrogen-related receptor γ (ERRγ) plays a role in the differentiation of neuronal cells, we investigated whether an ERRγ ligand enhances adult neurogenesis and regulates depressive behavior in a LRRK2-G2019S-associated mouse model of PD. Young female LRRK2-G2019S mice (7-9 weeks old) showed depression-like behavior without dopaminergic neuronal loss in the nigrostriatal pathway nor motor dysfunction. A significant decrease in adult hippocampal neurogenesis was detected in young female LRRK2-G2019S mice, but not in comparable male mice. A synthetic ERRγ ligand, (E)-4-hydroxy-N'-(4-(phenylethynyl)benzylidene)benzohydrazide (HPB2), ameliorated depression-like behavior in young female LRRK2-G2019S mice and enhanced neurogenesis in the hippocampus, as evidenced by increases in the number of bromodeoxyuridine/neuronal nuclei-positive cells and in the intensity and number of doublecortin-positive cells in the hippocampal dentate gyrus (DG). Moreover, HPB2 significantly increased the number of spines and the number and length of dendrites in the DG of young female LRRK2-G2019S mice. Furthermore, HPB2 upregulated brain-derived neurotrophic factor (BDNF)/tropomyosin receptor kinase B (TrkB) signaling, one of the important factors regulating neurogenesis, as well as phosphorylated cAMP-response element binding protein-positive cells in the DG of young female LRRK2-G2019S mice. Together, these results suggest ERRγ as a novel therapeutic target for PD-associated depression by modulating adult neurogenesis and BDNF/TrkB signaling.

Monogenetic Forms of Parkinson’s Disease – Bridging the Gap Between Genetics and Biomarkers

The therapy of neurodegenerative diseases such as Parkinson’s disease (PD) is still limited to the treatment of symptoms and primarily aimed at compensating for dopaminergic hypofunction. Numerous disease-modifying therapies currently in the pipeline attempt to modify the underlying pathomechanisms. In recent decades, the results of molecular genetics and biomarker research have raised hopes of earlier diagnosis and new neuroprotective therapeutic approaches. As the disease-causing processes in monogenetic forms of PD are better understood than in sporadic PD, these disease subsets are likely to benefit first from disease-modifying therapies. Recent studies have suggested that disease-relevant changes found in genetically linked forms of PD (i.e., PARK-LRRK2, PARK-GBA) can also be reproduced in patients in whom no genetic cause can be found, i.e., those with sporadic PD. It can, therefore, be assumed that as soon as the first causal therapy for genetic forms of PD is approved, more patients with PD will undergo genetic testing and counseling. Regarding future neuroprotective trials in neurodegenerative diseases and objective parameters such as biomarkers with high sensitivity and specificity for the diagnosis and course of the disease are needed. These biomarkers will also serve to monitor treatment success in clinical trials. Promising examples in PD, such as alpha-synuclein species, lysosomal enzymes, markers of amyloid and tau pathology, and neurofilament light chain, are under investigation in blood and CSF. This paper provides an overview of the opportunities and current limitations of monogenetic diagnostic and biomarker research in PD and aims to build a bridge between current knowledge and association with PD genetics and biomarkers.

The C-Terminal Domain of LRRK2 with the G2019S Substitution Increases Mutant A53T α-Synuclein Toxicity in Dopaminergic Neurons In Vivo

Alpha-synuclein (α-syn) and leucine-rich repeat kinase 2 (LRRK2) play crucial roles in Parkinson's disease (PD). They may functionally interact to induce the degeneration of dopaminergic (DA) neurons via mechanisms that are not yet fully understood. We previously showed that the C-terminal portion of LRRK2 (ΔLRRK2) with the G2019S mutation (ΔLRRK2^G2019S) was sufficient to induce neurodegeneration of DA neurons in vivo, suggesting that mutated LRRK2 induces neurotoxicity through mechanisms that are (i) independent of the N-terminal domains and (ii) "cell-autonomous". Here, we explored whether ΔLRRK2^G2019S could modify α-syn toxicity through these two mechanisms. We used a co-transduction approach in rats with AAV vectors encoding ΔLRRK2^G2019S or its "dead" kinase form, ΔLRRK2^DK, and human α-syn with the A53T mutation (AAV-α-syn^A53T). Behavioral and histological evaluations were performed at 6- and 15-weeks post-injection. Results showed that neither form of ΔLRRK2 alone induced the degeneration of neurons at these post-injection time points. By contrast, injection of AAV-α-syn^A53T alone resulted in motor signs and degeneration of DA neurons. Co-injection of AAV-α-syn^A53T with AAV-ΔLRRK2^G2019S induced DA neuron degeneration that was significantly higher than that induced by AAV-α-syn^A53T alone or with AAV-ΔLRRK2^DK. Thus, mutated α-syn neurotoxicity can be enhanced by the C-terminal domain of LRRK2^G2019 alone^, through cell-autonomous mechanisms.

Mind the Gap: LRRK2 Phenotypes in the Clinic vs. in Patient Cells

Mutations in the Parkinson's disease (PD) protein Leucine Rich Repeat Kinase 2 (LRRK2) have been under study for more than 15 years and our understanding of the cellular phenotypes for the pathogenic mutant forms of LRRK2 has significantly advanced. In parallel to research on LRRK2 mutations in experimental systems, clinical characterization of patients carrying LRRK2 mutations has advanced, as has the analysis of cells that are derived from these patients, including fibroblasts, blood-derived cells, or cells rendered pluripotent. Under the hypothesis that patient clinical phenotypes are a consequence of a cascade of underlying molecular mechanisms gone astray, we currently have a unique opportunity to compare findings from patients and patient-derived cells to ask the question of whether the clinical phenotype of LRRK2 Parkinson's disease and cellular phenotypes of LRRK2 patient-derived cells may be mutually informative. In this review, we aim to summarize the available information on phenotypes of LRRK2 mutations in the clinic, in patient-derived cells, and in experimental models in order to better understand the relationship between the three at the molecular and cellular levels and identify trends and gaps in correlating the data.

Progression and treatment of a series of patients with advanced LRRK2-associated Parkinson's disease

INTRODUCTION

LRRK2 mutations have traditionally been associated with a benign phenotype of Parkinson's disease (PD). Favourable responses to deep brain stimulation (DBS) are reported in the advanced phase.

METHODS

We performed a retrospective analysis of the clinical characteristics and progression of 13 patients with LRRK2-associated PD (13 with G2019S and one with I1371 V). Nine patients were in the advanced phase, with a mean progression time of 7.2 years before reaching this phase.

RESULTS

Seven patients underwent bilateral subthalamic DBS implantation, and two received infusion treatment. Patients with mutation G2019S responded excellently to DBS, with Unified Parkinson's disease rating scale (UPDRS) II and III scores improving by 80% at six months. This response was sustained over time. The patient with mutation I1371 V had a severe phenotype of the disease, and presented a moderate response to DBS. Patients with advanced LRRK2-associated PD showed predominantly frontal cognitive involvement, with significant language impairment.

CONCLUSIONS

In these patients, progression was faster in the advanced stage of the disease. We emphasise the suitability of subthalamic DBS in the management of these patients.

Dementia with Lewy bodies in first-generation immigrants in a European memory clinic

We wanted to explore possible differences in disease presentation, frequency, and age of onset of dementia with Lewy bodies (DLB) between first-generation immigrants (FGI) and patients born in Belgium (PBIB). We conducted a retrospective study on all patients of our Memory Clinic between June 1, 2010 and January 31, 2020. A synucleinopathy was diagnosed in 150 of 2702 patients (5.5%): 91 received a diagnosis of DLB (3.4%). FGI were two times more likely to receive a diagnosis of DLB, due to a higher prevalence in North-Africans and Latin-Americans. Visual hallucinations were less frequent in North-Africans than in other immigrants. FGI were younger than PBIB and reported more often parasomnia. Our data suggest a higher risk for DLB in certain immigrant groups. Especially for North-African patients, a genetic factor can be suspected, namely mutations in Leucine-rich repeat kinase 2 (LRRK2). Memory clinics with a high rate of FGI may provide interesting data and insights into the prevalence of DLB, genetic and environmental differences.

Global and Regional Changes in Perivascular Space in Idiopathic and Familial Parkinson's Disease

BACKGROUND

The glymphatic system, including the perivascular space (PVS), plays a critical role in brain homeostasis. Although mounting evidence from Alzheimer's disease has supported the potential role of PVS in neurodegenerative disorders, its contribution in Parkinson's disease (PD) has not been fully elucidated. Although idiopathic (IPD) and familial PD (FPD) share similar pathophysiology in terms of protein aggregation, the differential impact of PVS on PD subtypes remains unknown. Our objective was to examine the differences in PVS volume fraction in IPD and FPD compared to healthy controls (HCs) and nonmanifest carriers (NMCs).

METHODS

A total of 470 individuals were analyzed from the Parkinson's Progression Markers Initiative database, including (1) IPD (n = 179), (2) FPD (LRRK2 [leucine-rich repeat kinase 2], glucocerebrosidase, or α-synuclein) (n = 67), (3) NMC (n = 101), and (4) HCs (n = 84). Total PVS volume fraction (%) was compared using parcellation and quantitation within greater white matter volume at global and regional levels in all cortical and subcortical white matter.

RESULTS

There was a significant increase in global and regional PVS volume fraction in PD versus non-PD, particularly in FPD versus NMC and LRRK2 FPD versus NMC. Regionally, FPD and NMC differed in the medial orbitofrontal region, as did LRRK2 FPD versus NMC. Non-PD and PD differed in the medial orbitofrontal region and the banks of the superior temporal regions. IPD and FPD differed in the cuneus and lateral occipital regions.

CONCLUSIONS

Our findings support the role of PVS in PD and highlight a potentially significant contribution of PVS to the pathophysiology of FPD, particularly LRRK2. © 2021 International Parkinson and Movement Disorder Society.

Atypical parkinsonian syndromes in a North African tertiary referral center

INTRODUCTION

Data on epidemiology of atypical parkinsonian syndromes (APS) in North African countries are limited. Our objective was to study the epidemiological features of APS in a Tunisian population.

METHODS

We conducted a 17-year retrospective cross-sectional descriptive study in the Department of Neurology at Razi University Hospital. We included all patients responding to consensus diagnosis criteria of APS. We recorded demographic and clinical data. Group differences were assessed with a post hoc ANOVA with a Bonferroni error correction.

RESULTS

We included 464 APS patients. Hospital prevalence of APS among all parkinsonism cases was 20.6%. Mean annual increase of incidence defined as newly diagnosed APS cases per year reached 38.8%/year. APS were divided into 4 etiological subgroups: dementia with Lewy bodies (DLB; 56.7%); progressive supranuclear palsy(PSP; 16.2%); multiple system atrophy (MSA; 14.6%); and finally corticobasal syndrome (CBS; 12.5%). Sex-ratio was 1.2. This male predominance was found in all subgroups except MSA (p = .013). Mean age at onset was 68.5 years, most belated in DLB (69.7 years; p < .001). Young-onset parkinsonism (<40 years) was found only in MSA subgroup (p = .031). Parkinsonism was of late onset (>70 years) in 50.7% of patients and was significantly associated with DLB subgroup (p = .013). Inaugural parkinsonism was associated with CBS and MSA (p = .0497), and gait disorders at disease onset were associated with PSP and MSA (p = .0062). Cognitive and mood disorders were more marked in DLB and most preserved in MSA. Consanguinity was more marked in CBS (p = .037), and family history of dementia and psychiatric diseases was more common in DLB. Thirty-seven families with similar cases of APS were identified.

CONCLUSIONS

This is the largest African epidemiological study on APS. In our population, APS were frequent and dominated by DLB. The age of onset of parkinsonism was the most decisive feature for differential diagnosis.

Genetic and Phenotypic Basis of Autosomal Dominant Parkinson's Disease in a Large Multi-Center Cohort

LRRK2, SNCA, and VPS35 are unequivocally associated with autosomal dominant Parkinson's disease (PD). We evaluated the prevalence of LRRK2, SNCA, and VPS35 mutations and associated clinical features in a large French multi-center cohort of PD patients. Demographic and clinical data were collected for 1,805 index cases (592 with autosomal dominant inheritance and 1,213 isolated cases) since 1990. All probands were screened with TaqMan assays for LRRK2 Gly2019Ser. In the absence of this mutation, the coding sequences of the three genes were analyzed by Sanger sequencing and/or next-generation sequencing. The data for the three genes were analyzed according to age at onset, family history, ethnic origin and clinical features. We identified 160 index cases (8.9%) with known pathogenic variants: 138 with pathogenic LRRK2 variants (7.6%), including 136 with the Gly2019Ser mutation, 19 with SNCA point mutations or genomic rearrangements (1.1%), and three with the VPS35 Asp620Asn mutation (0.16%). Mutation frequencies were higher in familial than isolated cases, consistent with autosomal dominant inheritance (12.0 vs. 7.3%; OR 1.7, 95% CI [1.2-2.4], p = 0.001). PD patients with LRRK2 variants were more likely to have higher rates of late-onset PD (>50 years; OR 1.5, 95% CI [1.0-2.1], p = 0.03), whereas those with SNCA mutations tended to have earlier age at onset disease (≤ 50 years, p = 0.06). The clinical features of LRRK2 carriers and those without any pathogenic variants in known PD-associated genes were similar. The likelihood of detecting disease-causing mutations was higher in cases compatible with autosomal dominant inheritance.

Parkinson's Disease Research on the African Continent: Obstacles and Opportunities

The burden of Parkinson's disease (PD) is becoming increasingly important in the context of an aging African population. Although PD has been extensively investigated with respect to its environmental and genetic etiology in various populations across the globe, studies on the African continent remain limited. In this Perspective article, we review some of the obstacles that are limiting research and creating barriers for future studies. We summarize what research is being done in four sub-Saharan countries and what the key elements are that are needed to take research to the next level. We note that there is large variation in neurological and genetic research capacity across the continent, and many opportunities for unexplored areas in African PD research. Only a handful of countries possess appropriate infrastructure and personnel, whereas the majority have yet to develop such capacity. Resource-constrained environments strongly determines the possibilities of performing research locally, and unidirectional export of biological samples and genetic data remains a concern. Local-regional partnerships, in collaboration with global PD consortia, should form an ethically appropriate solution, which will lead to a reduction in inequality and promote capacity building on the African continent.

LRRK2 and GBA Variants Exert Distinct Influences on Parkinson's Disease-Specific Metabolic Networks

The natural history of idiopathic Parkinson's disease (PD) varies considerably across patients. While PD is generally sporadic, there are known genetic influences: the two most common, mutations in the LRRK2 or GBA1 gene, are associated with slower and more aggressive progression, respectively. Here, we applied graph theory to metabolic brain imaging to understand the effects of genotype on the organization of previously established PD-specific networks. We found that closely matched PD patient groups with the LRRK2-G2019S mutation (PD-LRRK2) or GBA1 variants (PD-GBA) expressed the same disease networks as sporadic disease (sPD), but PD-LRRK2 and PD-GBA patients exhibited abnormal increases in network connectivity that were not present in sPD. Using a community detection strategy, we found that the location and modular distribution of these connections differed strikingly across genotypes. In PD-LRRK2, connections were gained within the network core, with the formation of distinct functional pathways linking the cerebellum and putamen. In PD-GBA, by contrast, the majority of functional connections were formed outside the core, involving corticocortical pathways at the network periphery. Strategically localized connections within the core in PD-LRRK2 may maintain PD network activity at lower levels than in PD-GBA, resulting in a less aggressive clinical course.