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Since the first publication about the role of mutations in the GBA gene in Parkinson's disease (PD) 25 years ago and the about the G2019S-LRRK2 15 years ago much has been happened. The story is of special interest among the Ashkenazi Jews (AJ), where the frequency of mutations in those 2 genes is as high as 10% in the AJ general population and about 35% among AJ-PD patients.

Such high frequencies give an opportunity to learn about the contribution of those mutations to the clinical course as well as response to treatment. Furthermore, the large number of subjects at risk within the AJ population is a unique opportunity to better understand the prodromal stage of PD and potential environmental, behavioral and genetic modifiers of the risk to develop PD.

Recent observation from several cohorts have reported that the natural course of GBA-PD and G2019S-LRRK2-PD are significantly different and that dual mutations are behaving differently suggesting a protective effect of G2019S-LRRK2 in patients with GBA-PD.

The talk will summarize the literature and will present recent findings about the longitudinal course of genetic PD. I will also highlight the personalized approach to AJ PD patients based on the genetic status and the predominant clinical syndrome.

Aims

The LRRK2 p.G2019S Parkinson’s disease (PD)-associated variant is associated with glucocerebrosidase (GCase) activity in peripheral blood. We aimed to evaluate the effects of other LRRK2 variants on GCase activity in peripheral blood and estimate their association with PD.

Methods

LRRK2 and GBA were fully sequenced in 1,123 PD patients and 576 controls from two cohorts. GCase activity was measured in dried blood spots by liquid chromatography-tandem mass spectrometry in the Columbia University cohort from New York and in the Parkinson’s Progression Markers Initiative (PPMI) cohort. To test the association between LRRK2 variants and GCase activity, linear regression adjusted for age, sex, PD status and GBA status was performed.

Results

LRRK2 p.M1646T was associated with increased GCase activity in the Columbia University cohort (β=1.58, p=0.0003), and increased but not significantly in the PPMI cohort (β=0.29, p=0.58). p.M1646T was associated with PD in 37,688 PD patients, 18,618 UK Biobank proxy-cases and 1.4 million controls from the International Parkinson’s Disease Genomic Consortium (IPDGC) (OR=1.18, 95% CI=1.09-1.28, p=7.33E-05).

Conclusions

Our results suggest that the p.M1646T variant is associated with risk of PD with a small effect and with increased GCase activity in peripheral blood.

Aims

There is increasing evidence showing that LRRK2 mutations are associated with a milder clinical phenotype and preserved cholinergic function in Parkinson’s disease (PD). The basal forebrain (BF) is a dominantly cortically-projecting cholinergic area of the brain. In this study we aimed to assess whether BF volumes change in LRRK2 carriers with and without PD as well as their association with longitudinal cognitive functions.

Methods

Thirty-two symptomatic LRRK2-PD patients and 13 asymptomatic LRRK2 individuals were included from the Parkinson's Progression Markers Initiative. In addition, 32 patients with idiopathic PD (iPD) and 13 healthy controls matched to the previous groups were included. BF and other gray matter volumes were extracted from baseline T1-weighted MRI scans using previously established procedures. We compared BF volumes between groups and assessed their relationship with longitudinal cognitive changes using linear mixed effects models. Finally, mediation analyses assessed whether BF volumes mediated differences in cognitive trajectories between LRRK2-PD and iPD.

Results

LRRK2-PD patients showed significantly higher BF volumes compared to iPD (p=0.019) as did asymptomatic LRRK2 subjects compared to controls (p=0.008). No other brain regions showed increased volumes in LRRK2-PD and asymptomatic LRRK2. BF volumes predicted longitudinal decline in several cognitive functions in iPD patients but not in LRRK2-PD, who did not show cognitive changes over time. BF volumes significantly mediated the different cognitive trajectories between iPD and LRRK2-PD patients (bootstrap 95% CI 0.056-2.955).

Conclusions

Mutations in LRRK2 are associated with increased BF volumes, potentially reflecting a compensatory hypercholinergic state that could prevent cognitive decline in LRRK2-PD patients.

Aims

Glucocerebrosidase gene (GBA) mutations are the greatest genetic cause of Parkinson’s disease (PD). We studied the longitudinal disease course of GBA-positive compared to GBA-negative patients along a 5-year follow-up, evaluating changes in cortical thickness and clinical outcomes.

Methods

10 GBA-positive PD and 20 GBA-negative PD matched for age, sex, disease duration and severity underwent clinical, neuropsychological and MRI assessments at study entry and once a year for 5 years. At baseline and at the last visit, each group of patients was compared in terms of cortical thinning to a group of 22 age-matched healthy controls (HC), who underwent one MRI at the study entry. Clinical, cognitive and cortical features were compared between patient groups at baseline and over time.

Results

At baseline, GBA-positive and GBA-negative patients had similar clinical and cognitive profiles. Compared to GBA-negative and HC, GBA-positive patients showed cortical thinning of the left temporal, parietal and occipital gyri. Over time, compared to GBA-negative PD, GBA-positive worsened significantly in motor symptoms and showed a greater pattern of bilateral cortical thinning involving also frontal cortices. After 60 months, compared to HC, GBA-negative PD showed a pattern of cortical thinning similar to that showed by GBA-positive at baseline.

Conclusions

Compared to GBA-negative, GBA-positive PD patients showed a greater and earlier cortical thinning which worsened over time. GBA-negative PD patients reached the pattern of cortical thinning of GBA-positive at the baseline only after 5 years, reflecting a slower disease progression.

Supported by: Ministry of Education and Science Republic of Serbia (Grant #175090).

Aims

Lewy body dementia (LBD) includes Parkinson’s disease dementia and dementia with Lewy bodies, both characterized by abnormal deposition of alpha-synuclein in the brain (Lewy bodies). Several studies suggest that genes such as SNCA, APOE, and GBA are involved in LBD. In particular, heterozygous mutations in GBA are associated with an increased risk of LBD and Parkinson’s disease (PD); however is not fully understood why individuals with the same GBA variant eventually develop PD or LBD. Here, we compared the burden of deleterious variants in dementia-related genes in LBD vs. PD patients carriers of a GBA mutation.

Methods

We studied a cohort composed of 204 PD and 135 LBD patients heterozygous for at least 1 PD-related GBA mutation using an HaloPlex NGS custom panel including 10 dementia-related genes. All identified variations were validated by Sanger sequencing.

Results

Among the identified variants, we firstly selected the ones already known to be associated with dementia and the variations with a clear effect on protein (frameshift, splicing, nonsense mutations). Then we classified the other variants according to their potential pathogenicity using as threshold a CADD score >20. Our main result is that a second GBA mutation is more frequent in LBD (8.1%) vs PD (4.4%).

Conclusions

We found that the presence of a second deleterious mutation in GBA is the main modulator of the risk to develop dementia. The identification of additional genetic factors increasing the LBD risk could be helpful for early diagnosis and for the discovery of novel therapeutic strategies.

Aims

Mutations of GBA(encoding for glucocerebrosidase, GCase) represent the major genetic risk factors for Parkinson’s disease (PD). Modifiers responsible for phenoconversion in manifesting carriers are still unknown. GCase is active in monocytes and macrophages and recent studies showed a role of the innate immune system in PD. We performed an integrated transcriptomic analysis of CD14+ monocytes to assess PD mechanisms associated with GBAmutations.

Methods

We enrolled a cohort of subjects with PD and controls (CTRL) with and without GBA mutations (GBA+ and GBA-). CD14+ monocytes were purified from the peripheral blood and RNA and DNA were isolated according to standard protocol. RNA was sequenced at 60M reads per sample (Illumina HiSeq 2500). Genotyping was performed (Illumina Global Screening Array, ~700K SNPs).

Results

Data from a cohort of 56 PD-GBA-, 23 PD-GBA+, 66 CTRL-GBA-, and 13 CTRL-GBA+ were analyzed. Differential expression profiles with nested manually designed interaction model showed an enrichment of pathways related to immune response, exocytosis and RNA processing in manifesting vs non manifesting GBA carriers, and of alpha-synuclein and amyloid related genes in PD-GBA+ vs PD-GBA-. The study of genetic outliers (as assessed with the tool OUTRIDER) showed enrichment of genes related to autophagy and exocytosis in PD-GBA+ group.

Conclusions

Our data suggests that CD14+ monocytes are differently activated in manifesting and non-manifesting GBAcarriers and deregulated pathways are relevant for PD pathogenesis. Thus the study of these cells in the context of GBA-PD can open the way to the discovery of disease modifiers and possible biomarkers.

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Novel Therapies for GBA-Parkinson disease

Anthony HV Schapira

University Department of Clinical and Movement Neurosciences, UCL Queen Square Institute of Neurology, London

Mutations of the glucocerebrosidase (GBA) gene cause autosomal recessive Gaucher disease and are the most important risk factor for the development of Parkinson disease (PD). It is estimated that 10-15% of PD patients carry GBA mutations; this increases to 25% in the Ashkenazi population. The penetrance of PD in GBA carriers is approximately 30% by age 80 years.

Several in vitro and in vivo studies have demonstrated a bi-directional reciprocal relationship between GBA enzyme activity (GCase) and alpha-synuclein levels. The precise mechanisms underlying this relationship are not fully understood and may involve several factors including direct interactions of GCase with alpha-synuclein, substrate accumulation and altered lipid composition and function. We have hypothesized that increasing GCase activity will reduce alpha-synuclein levels.

GCase activity may be increased by enhancing transcription or transfection of the wild-type gene, or re-folding and chaperoning the mutant protein to the lysosome. The latter pathway has been the target of several recent studies to determine if elevating GCase protein and activity lowers alpha-synuclein. We have used the GCase chaperones ambroxol and isofagomine in in vitro and in vivo models of the N370S and L444P GBA mutations, these represent the commonest pathogenic mutations associated with PD.

Treatment with ambroxol, a GCase chaperone and transcription factor (TFEB) enhancer, increased GCase levels and activity and reduced alpha-synuclein. Chaperone treatment of Drosophila expressing GBA mutant proteins protected against loss of dopaminergic neurons and restored motor function. Ambroxol increased GCase in both L444P and wild-type mouse brain, and reduced brain alpha-synuclein levels in mice over-expressing alpha-synuclein. The first clinical trial of genetically stratified PD subjects used ambroxol in a Phase II study to confirm safety, brain penetration and target engagement by increasing GCase levels in the CSF (JAMA Neurology 2020; 77:427-434). A Phase III study is now planned to determine if the drug can slow clinical progression in PD. Other compounds that enhance GCase activity are in Phase II clinical trial.

Alternative strategies include substrate reduction therapy using venglustat, a glucosylceramide synthase inhibitor. This drug is currently in a Phase II study in GBA-PD to assess safety and target engagement, with an extension to assess impact on clinical progression over 12 months. Gene-based therapies are also in Phase II development with the intention of using CND-delivered wild-type GBA and vector to increase GCase levels and production.

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Our work shows that Parkinson’s disease (PD), related dementias and experimental in vivo models, can be caused by primary pathogenesis in lipid pathways (Isacson et al 2019 Front. Neurol.; Hallett et al 2019 J Neuroinflammation). By copying mechanisms seen in lysosomal storage disorders, such as Gaucher disease and related disorders, in a chronic, age- and dose-dependent manner, glycolipid cell metabolism can lead to PD, neurodegeneration and neuroinflammation. Deficiencies in several lysosomal hydrolases in animal models causes formation of high-molecular weight alpha-synuclein and ubiquitin. Lysosomal enzyme gene therapy in the substantia nigra reduces embedding of alpha-synuclein in lipid compartments and rescues dopaminergic neurons from degeneration (Rocha et al 2015 Neurobio. Dis.; Brekk et al, 2020 Acta. Neuropathol. Comm.).

Disturbed relationships in lipid homeostasis that causes neuropathology to develop over time and with age, includes altered mechanisms of glia-neuron exchange of lipids and inflammatory signals. Neurons are dependent on proper lipid transport to neighboring glia for lipid exchange and disposal of potentially lipotoxic metabolites, producing distinct lipid distribution profiles amongst various cell-types of the central nervous system. Our data shows that intracellular lipids are accumulated in neurons and microglia in the PD substantia nigra, and this is recapitulated by experimental in vivo inhibition of glucocerebrosidase.

These new results are consistent with a paradigm shift where lipid abnormalities are central to or preceding protein changes typically associated with PD and related disorders. Agents or therapies that restore lipid homeostasis between neurons, astrocytes, and microglia could potentially correct PD pathogenesis and disease progression.

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