Longitudinal Measurements of Glucocerebrosidase activity in Parkinson's patients

GBA1-Associated Parkinson's Disease Is a Distinct Entity

GBA1-associated Parkinson's disease (GBA1-PD) is increasingly recognized as a distinct entity within the spectrum of parkinsonian disorders. This review explores the unique pathophysiological features, clinical progression, and genetic underpinnings that differentiate GBA1-PD from idiopathic Parkinson's disease (iPD). GBA1-PD typically presents with earlier onset and more rapid progression, with a poor response to standard PD medications. It is marked by pronounced cognitive impairment and a higher burden of non-motor symptoms compared to iPD. Additionally, patients with GBA1-PD often exhibit a broader distribution of Lewy bodies within the brain, accentuating neurodegenerative processes. The pathogenesis of GBA1-PD is closely associated with mutations in the GBA1 gene, which encodes the lysosomal enzyme beta-glucocerebrosidase (GCase). In this review, we discuss two mechanisms by which GBA1 mutations contribute to disease development: 'haploinsufficiency,' where a single functional gene copy fails to produce a sufficient amount of GCase, and 'gain of function,' where the mutated GCase acquires harmful properties that directly impact cellular mechanisms for alpha-synuclein degradation, leading to alpha-synuclein aggregation and neuronal cell damage. Continued research is advancing our understanding of how these mechanisms contribute to the development and progression of GBA1-PD, with the 'gain of function' mechanism appearing to be the most plausible. This review also explores the implications of GBA1 mutations for therapeutic strategies, highlighting the need for early diagnosis and targeted interventions. Currently, small molecular chaperones have shown the most promising clinical results compared to other agents. This synthesis of clinical, pathological, and molecular aspects underscores the assertion that GBA1-PD is a distinct clinical and pathobiological PD phenotype, necessitating specific management and research approaches to better understand and treat this debilitating condition.

Genome-wide association study of glucocerebrosidase activity modifiers

One of the most common genetic risk factors for Parkinson's disease (PD) are variants in GBA1, which encodes the lysosomal enzyme glucocerebrosidase (GCase). GCase deficiency has been associated with an increased PD risk, but not all individuals with low GCase activity are carriers of GBA1 mutations, suggesting other factors may be acting as modifiers. We aimed to discover common variants associated with GCase activity, as well as replicate previously reported associations, by performing a genome-wide association study using two independent cohorts: a Columbia University cohort consisting of 697 PD cases and 347 controls and the Parkinson's Progression Markers Initiative (PPMI) cohort consisting of 357 PD cases and 163 controls. As expected, GBA1 variants have the strongest association with decreased activity, led by p.N370S (beta = -4.36, se = 0.32, p = 5.05e-43). We also identify a novel association in the GAA locus (encoding for acid alpha-glucosidase, beta = -0.96, se = 0.17, p = 5.23e-09) that may be the result of an interaction between GCase and acid alpha-glucosidase based on various interaction analyses. Lastly, we show that several PD-risk loci are potentially associated with GCase activity. Further research will be needed to replicate and validate our findings and to uncover the functional connection between acid alpha-glucosidase and GCase.

p.L1795F LRRK2 variant is a common cause of Parkinson's disease in Central Europe

Pathogenic variants in LRRK2 are one of the most common genetic risk factors for Parkinson's disease (PD). Recently, the lesser-known p.L1795F variant was proposed as a strong genetic risk factor for PD, however, further families are currently lacking in literature. A multicentre young onset and familial PD cohort (n = 220) from 9 movement disorder centres across Central Europe within the CEGEMOD consortium was screened for rare LRRK2 variants using whole exome sequencing data. We identified 4 PD cases with heterozygous p.L1795F variant. All 4 cases were characterised by akinetic-rigid PD phenotype with early onset of severe motor fluctuations, 2 receiving LCIG therapy and 2 implanted with STN DBS; all 4 cases showed unsatisfactory effect of advanced therapies on motor fluctuations. Our data also suggest that p.L1795F may represent the most common currently known pathogenic LRRK2 variant in Central Europe compared to the more studied p.G2019S, being present in 1.81% of PD cases within the Central European cohort and 3.23% of familial PD cases. Together with the ongoing clinical trials for LRRK2 inhibitors, this finding emphasises the urgent need for more ethnic diversity in PD genetic research.

A review on Gaucher disease: therapeutic potential of β-glucocerebrosidase-targeted mRNA/saRNA approach

Gaucher disease (GD), a rare hereditary lysosomal storage disorder, occurs due to a deficiency in the enzyme β-glucocerebrosidase (GCase). This deficiency leads to the buildup of substrate glucosylceramide (GlcCer) in macrophages, eventually resulting in various complications. Among its three types, GD2 is particularly severe with neurological involvements. Current treatments, such as enzyme replacement therapy (ERT), are not effective for GD2 and GD3 due to their inability to cross the blood-brain barrier (BBB). Other treatment approaches, such as gene or chaperone therapies are still in experimental stages. Additionally, GD treatments are costly and can have certain side effects. The successful use of messenger RNA (mRNA)-based vaccines for COVID-19 in 2020 has sparked interest in nucleic acid-based therapies. Remarkably, mRNA technology also offers a novel approach for protein replacement purposes. Additionally, self-amplifying RNA (saRNA) technology shows promise, potentially producing more protein at lower doses. This review aims to explore the potential of a cost-effective mRNA/saRNA-based approach for GD therapy. The use of GCase-mRNA/saRNA as a protein replacement therapy could offer a new and promising direction for improving the quality of life and extending the lifespan of individuals with GD.

Altered Sphingolipid Hydrolase Activities and Alpha-Synuclein Level in Late-Onset Schizophrenia

Recent data described that patients with lysosomal storage disorders (LSDs) may have clinical schizophrenia (SCZ) features. Disruption of lipid metabolism in SCZ pathogenesis was found. Clinical features of schizophrenia (SCZ) have been demonstrated in patients with several lysosomal storage disorders (LSDs). Taking into account the critical role of lysosomal function for neuronal cells' lysosomal dysfunction could be proposed in SCZ pathogenesis. The current study analyzed lysosomal enzyme activities and the alpha-synuclein level in the blood of patients with late-onset SCZ. In total, 52 SCZ patients with late-onset SCZ, 180 sporadic Parkinson's disease (sPD) patients, and 176 controls were recruited. The enzymatic activity of enzymes associated with mucopolysaccharidosis (alpha-L-Iduronidase (IDUA)), glycogenosis (acid alpha-glucosidase (GAA)) and sphingolipidosis (galactosylceramidase (GALC), glucocerebrosidase (GCase), alpha-galactosidase (GLA), acid sphingomyelinase (ASMase)) and concentration of lysosphingolipids (hexosylsphingosine (HexSph), globotriaosylsphingosine (LysoGb3), and lysosphingomyelin (LysoSM)) were measured using LC-MS/MS. The alpha-synuclein level was estimated in magnetically separated CD45+ blood cells using the enzyme-linked immunosorbent assay (ELISA). Additionally, NGS analysis of 11 LSDs genes was conducted in 21 early-onset SCZ patients and 23 controls using the gene panel PGRNseq-NDD. Decreased ASMase, increased GLA activities, and increased HexSpn, LysoGb3, and LysoSM concentrations along with an accumulation of the alpha-synuclein level were observed in late-onset SCZ patients in comparison to the controls (p < 0.05). Four rare deleterious variants among LSDs genes causing mucopolysaccharidosis type I (IDUA (rs532731688, rs74385837) and type III (HGSNAT (rs766835582)) and sphingolipidosis (metachromatic leukodystrophy (ARSA (rs201251634)) were identified in five patients from the group of early-onset SCZ patients but not in the controls. Our findings supported the role of sphingolipid metabolism in SCZ pathogenesis. Aberrant enzyme activities and compounds of sphingolipids associated with ceramide metabolism may lead to accumulation of alpha-synuclein and may be critical in SCZ pathogenesis.

Fiber-Specific White Matter Alterations in Parkinson's Disease Patients with GBA Gene Mutations

BACKGROUND

Patients with Parkinson's disease (PD) carrying GBA gene mutations (GBA-PD) have a more aggressive disease course than those with idiopathic PD (iPD).

OBJECTIVE

The objective of this study was to investigate fiber-specific white matter (WM) differences in nonmedicated patients with early-stage GBA-PD and iPD using fixel-based analysis, a novel technique to assess tract-specific WM microstructural and macrostructural features comprehensively.

METHODS

Fixel-based metrics, including microstructural fiber density (FD), macrostructural fiber-bundle cross section (FC), and a combination of FD and FC (FDC), were compared among 30 healthy control subjects, 16 patients with GBA-PD, and 35 patients with iPD. Associations between FDC and clinical evaluations were also explored using multiple linear regression analyses.

RESULTS

Patients with GBA-PD showed significantly lower FD in the fornix and superior longitudinal fasciculus than healthy control subjects, and lower FC in the corticospinal tract (CST) and lower FDC in the CST, middle cerebellar peduncle, and striatal-thalamo-cortical pathways than patients with iPD. Contrarily, patients with iPD showed significantly higher FC and FDC in the CST and striatal-thalamo-cortical pathways than healthy control subjects. In addition, lower FDC in patients with GBA-PD was associated with reduced glucocerebrosidase enzyme activity, lower cerebrospinal fluid total α-synuclein levels, lower Montreal Cognitive Assessment scores, lower striatal binding ratio, and higher Unified Parkinson's Disease Rating Scale Part III scores.

CONCLUSIONS

We report reduced fiber-specific WM density and bundle cross-sectional size in patients with GBA-PD, suggesting neurodegeneration linked to glucocerebrosidase deficiency, α-synuclein accumulation, and poorer cognition and motor functions. Conversely, patients with iPD showed increased fiber bundle size, likely because of WM reorganization. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

GBA1 Variants and Parkinson's Disease: Paving the Way for Targeted Therapy

Glucosylceramidase beta 1 (GBA1) variants have attracted enormous attention as the most promising and important genetic candidates for precision medicine in Parkinson's disease (PD). A substantial correlation between GBA1 genotypes and PD phenotypes could inform the prediction of disease progression and promote the development of a preventive intervention for individuals at a higher risk of a worse disease prognosis. Moreover, the GBA1-regulated pathway provides new perspectives on the pathogenesis of PD, such as dysregulated sphingolipid metabolism, impaired protein quality control, and disrupted endoplasmic reticulum-Golgi trafficking. These perspectives have led to the development of novel disease-modifying therapies for PD targeting the GBA1-regulated pathway by repositioning treatment strategies for Gaucher's disease. This review summarizes the current hypotheses on a mechanistic link between GBA1 variants and PD and possible therapeutic options for modulating GBA1-regulated pathways in PD patients.

Role of novel endpoints and evaluations of response in Parkinson disease

With progress in our understanding of Parkinson disease (PD) and other neurodegenerative disorders, from clinical features to imaging, genetic, and molecular characterization comes the opportunity to refine and revise how we measure these diseases and what outcome measures are used as endpoints in clinical trials. While several rater-, patient-, and milestone-based outcomes for PD exist that may serve as clinical trial endpoints, there remains an unmet need for endpoints that are clinically meaningful, patient centric while also being more objective and quantitative, less susceptible to effects of symptomatic therapy (for disease-modification trials), and that can be measured over a short period and yet accurately represent longer-term outcomes. Several novel outcomes that may be used as endpoints in PD clinical trials are in development, including digital measures of signs and symptoms, as well a growing array of imaging and biospecimen biomarkers. This chapter provides an overview of the state of PD outcome measures as of 2022, including considerations for selection of clinical trial endpoints in PD, advantages and limitations of existing measures, and emerging potential novel endpoints.

The GBA variant E326K is associated with alpha-synuclein aggregation and lipid droplet accumulation in human cell lines

Sequence variants or mutations in the GBA gene are numerically the most important risk factor for Parkinson disease (PD). The GBA gene encodes for the lysosomal hydrolase enzyme, glucocerebrosidase (GCase). GBA mutations often reduce GCase activity and lead to the impairment of the autophagy-lysosomal pathway, which is important in the turnover of alpha-synuclein, accumulation of which is a key pathological hallmark of PD. Although the E326K variant is one of the most common GBA variants associated with PD, there is limited understanding of its biochemical effects. We have characterized homozygous and heterozygous E326K variants in human fibroblasts. We found that E326K variants did not cause a significant loss of GCase protein or activity, endoplasmic reticulum (ER) retention or ER stress, in contrast to the L444P GBA mutation. This was confirmed in human dopaminergic SH-SY5Y neuroblastoma cell lines overexpressing GCase with either E326K or L444P protein. Despite no loss of the GCase activity, a significant increase in insoluble alpha-synuclein aggregates in E326K and L444P mutants was observed. Notably, SH-SY5Y overexpressing E326K demonstrated a significant increase in the lipid droplet number under basal conditions, which was exacerbated following treatment with the fatty acid oleic acid. Similarly, a significant increase in lipid droplet formation following lipid loading was observed in heterozygous and homozygous E326K fibroblasts. In conclusion, the work presented here demonstrates that the E326K mutation behaves differently to the common loss of function GBA mutations; however, lipid dyshomeostasis and alpha-synuclein pathology are still evident.

Association of CSF Glucocerebrosidase Activity With the Risk of Incident Dementia in Patients With Parkinson Disease

BACKGROUND AND OBJECTIVES

Variations in the glucocerebrosidase gene (GBA) are common risk factors for Parkinson disease (PD) and dementia in PD (PDD) and cause a reduction in the activity of the lysosomal enzyme glucocerebrosidase (GCase). It is anticipated that GCase dysfunction might contribute to a more malignant disease course and predict cognitive impairment in PD, although evidence is lacking. We aimed to discover whether CSF GCase activity is altered in newly diagnosed patients with PD and associated with future development of dementia.

METHODS

Patients with PD were participants of the ongoing population-based longitudinal ParkWest study in Southwestern Norway and were followed prospectively for up to 10 years. CSF was collected at diagnosis, and GBA carrier status was obtained. Control samples were from persons without neurodegenerative disorders. GCase activity was measured using a validated assay. PD dementia diagnosis was set according to the Movement Disorder Society criteria, and parametric accelerated failure time models were applied to analyze the association of GCase activity with dementia-free survival.

RESULTS

This study enrolled 117 patients with PD (mean age 67.2 years, including 12 GBA non-synonymous variant carriers) and 50 control participants (mean age 64 years). At the time of diagnosis, GCase activity was reduced in patients with PD with (mean ± SD, 0.92 ± 0.40 mU/mg, n = 12) or without GBA variations (1.00 ± 0.37 mU/mg, n = 105) compared with controls (1.20 ± 0.35, n = 50). GCase activity at the time of diagnosis was lower in patients with PD who developed dementia within 10 years (0.85 ± 0.27 mU/mg, n = 41) than in those who did not (1.07 ± 0.40 mU/mg, n = 76, p = 0.001). A 0.1-unit reduction in baseline GCase activity was associated with a faster development of PDD (hazard ratio 1.15, 95% CI 1.03-1.28, p = 0.014).

DISCUSSION

The association of early CSF GCase activity with long-term progression to PD dementia will have important implications for the design of clinical trials for GCase targeting therapies and patient management.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that reduced CSF GCase activity at the time of PD diagnosis is associated with an increased risk for later development of PDD.

GBA1 Gene Mutations in α-Synucleinopathies-Molecular Mechanisms Underlying Pathology and Their Clinical Significance

α-Synucleinopathies comprise a group of neurodegenerative diseases characterized by altered accumulation of a protein called α-synuclein inside neurons and glial cells. This aggregation leads to the formation of intraneuronal inclusions, Lewy bodies, that constitute the hallmark of α-synuclein pathology. The most prevalent α-synucleinopathies are Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). To date, only symptomatic treatment is available for these disorders, hence new approaches to their therapy are needed. It has been observed that GBA1 mutations are one of the most impactful risk factors for developing α-synucleinopathies such as PD and DLB. Mutations in the GBA1 gene, which encodes a lysosomal hydrolase β-glucocerebrosidase (GCase), cause a reduction in GCase activity and impaired α-synuclein metabolism. The most abundant GBA1 gene mutations are N370S or N409S, L444P/L483P and E326K/E365K. The mechanisms by which GCase impacts α-synuclein aggregation are poorly understood and need to be further investigated. Here, we discuss some of the potential interactions between α-synuclein and GCase and show how GBA1 mutations may impact the course of the most prevalent α-synucleinopathies.

Glucocerebrosidase mutations and Parkinson disease

The discovery of glucocerebrosidase (GBA1) mutations as the greatest numerical genetic risk factor for the development of Parkinson disease (PD) resulted in a paradigm shift within the research landscape. Efforts to elucidate the mechanisms behind GBA1-associated PD have highlighted shared pathways in idiopathic PD including the loss and gain-of-function hypotheses, endoplasmic reticulum stress, lipid metabolism, neuroinflammation, mitochondrial dysfunction and altered autophagy-lysosomal pathway responsible for degradation of aggregated and misfolded a-synuclein. GBA1-associated PD exhibits subtle differences in phenotype and disease progression compared to idiopathic counterparts notably an earlier age of onset, faster motor decline and greater frequency of non-motor symptoms (which also constitute a significant aspect of the prodromal phase of the disease). GBA1-targeted therapies have been developed and are being investigated in clinical trials. The most notable are Ambroxol, a small molecule chaperone, and Venglustat, a blood-brain-barrier-penetrant substrate reduction therapy agent. It is imperative that further studies clarify the aetiology of GBA1-associated PD, enabling the development of a greater abundance of targeted therapies in this new era of precision medicine.

GBA-associated PD: chances and obstacles for targeted treatment strategies

Given the clear role of GBA in the pathogenesis of Parkinson’s disease (PD) and its impact on phenotypical characteristics, this review provides an overview of the current knowledge of GBA-associated PD with a special focus on clinical trajectories and the underlying pathological mechanisms. Importantly, differences and characteristics based on mutation severity are recognized, and current as well as potential future treatment options are discussed. These findings will inform future strategies for patient stratification and cohort enrichment as well as suitable outcome measures when designing clinical trials.

GBA Variants and Parkinson Disease: Mechanisms and Treatments

The GBA gene encodes for the lysosomal enzyme glucocerebrosidase (GCase), which maintains glycosphingolipid homeostasis. Approximately 5–15% of PD patients have mutations in the GBA gene, making it numerically the most important genetic risk factor for Parkinson disease (PD). Clinically, GBA-associated PD is identical to sporadic PD, aside from the earlier age at onset (AAO), more frequent cognitive impairment and more rapid progression. Mutations in GBA can be associated with loss- and gain-of-function mechanisms. A key hallmark of PD is the presence of intraneuronal proteinaceous inclusions named Lewy bodies, which are made up primarily of alpha-synuclein. Mutations in the GBA gene may lead to loss of GCase activity and lysosomal dysfunction, which may impair alpha-synuclein metabolism. Models of GCase deficiency demonstrate dysfunction of the autophagic-lysosomal pathway and subsequent accumulation of alpha-synuclein. This dysfunction can also lead to aberrant lipid metabolism, including the accumulation of glycosphingolipids, glucosylceramide and glucosylsphingosine. Certain mutations cause GCase to be misfolded and retained in the endoplasmic reticulum (ER), activating stress responses including the unfolded protein response (UPR), which may contribute to neurodegeneration. In addition to these mechanisms, a GCase deficiency has also been associated with mitochondrial dysfunction and neuroinflammation, which have been implicated in the pathogenesis of PD. This review discusses the pathways associated with GBA-PD and highlights potential treatments which may act to target GCase and prevent neurodegeneration.

Impaired Sphingolipid Hydrolase Activities in Dementia with Lewy Bodies and Multiple System Atrophy

The synucleinopathies are a group of neurodegenerative diseases characterized by the oligomerization of alpha-synuclein protein in neurons or glial cells. Recent studies provide data that ceramide metabolism impairment may play a role in the pathogenesis of synucleinopathies due to its influence on alpha-synuclein accumulation. The aim of the current study was to assess changes in activities of enzymes involved in ceramide metabolism in patients with different synucleinopathies (Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA)). The study enrolled 163 PD, 44 DLB, and 30 MSA patients as well as 159 controls. Glucocerebrosidase, alpha-galactosidase, acid sphingomyelinase enzyme activities, and concentrations of the corresponding substrates (hexosylsphingosine, globotriaosylsphingosine, lysosphingomyelin) were measured by liquid chromatography tandem-mass spectrometry in blood. Expression levels of GBA, GLA, and SMPD1 genes encoding glucoceresobridase, alpha-galactosidase, and acid sphingomyelinase enzymes, correspondently, were analyzed by real-time PCR with TaqMan assay in CD45 + blood cells. Increased hexosylsphingosine concentration was observed in DLB and MSA patients in comparison to PD and controls (p < 0.001) and it was associated with earlier age at onset (AAO) of DLB (p = 0.0008). SMPD1 expression was decreased in MSA compared to controls (p = 0.015). Acid sphingomyelinase activity was decreased in DLB, MSA patients compared to PD patients (p < 0.0001, p < 0.0001, respectively), and in MSA compared to controls (p < 0.0001). Lower acid sphingomyelinase activity was associated with earlier AAO of PD (p = 0.012). Our data support the role of lysosomal dysfunction in the pathogenesis of synucleinopathies, namely, the pronounced alterations of lysosomal activities involved in ceramide metabolism in patients with MSA and DLB.

Evaluation of Strategies for Measuring Lysosomal Glucocerebrosidase Activity

Mutations in GBA1, which encode for the protein glucocerebrosidase (GCase), are the most common genetic risk factor for Parkinson's disease and dementia with Lewy bodies. In addition, growing evidence now suggests that the loss of GCase activity is also involved in onset of all forms of Parkinson's disease, dementia with Lewy bodies, and other dementias, such as progranulin-linked frontal temporal dementia. As a result, there is significant interest in developing GCase-targeted therapies that have the potential to stop or slow progression of these diseases. Despite this interest in GCase as a therapeutic target, there is significant inconsistency in the methodology for measuring GCase enzymatic activity in disease-modeling systems and patient populations, which could hinder progress in developing GCase therapies. In this review, we discuss the different strategies that have been developed to assess GCase activity and highlight the specific strengths and weaknesses of these approaches as well as the gaps that remain. We also discuss the current and potential role of these different methodologies in preclinical and clinical development of GCase-targeted therapies. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Glucocerebrosidase Activity is not Associated with Parkinson's Disease Risk or Severity

Background

Mutations in the GBA gene, which encodes the lysosomal enzyme glucocerebrosidase (GCase), are risk factors for Parkinson's disease (PD).

Objective

To explore the association between GCase activity, PD phenotype, and probability for prodromal PD among carriers of mutations in the GBA and LRRK2 genes.

Methods

Participants were genotyped for the G2019S‐LRRK2 and nine GBA mutations common in Ashkenazi Jews. Performance‐based measures enabling the calculation of the Movement Disorder Society (MDS) prodromal probability score were collected.

Results

One hundred and seventy PD patients (102 GBA‐PD, 38 LRRK2‐PD, and 30 idiopathic PD) and 221 non‐manifesting carriers (NMC) (129 GBA‐NMC, 45 LRRK2‐NMC, 15 GBA‐LRRK2‐NMC, and 32 healthy controls) participated in this study. GCase activity was lower among GBA‐PD (3.15 ± 0.85 μmol/L/h), GBA‐NMC (3.23 ± 0.91 μmol/L/h), and GBA‐LRRK2‐NMC (3.20 ± 0.93 μmol/L/h) compared to the other groups of participants, with no correlation to clinical phenotype.

Conclusions

Low GCase activity does not explain the clinical phenotype or risk for prodromal PD in this cohort. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society

Glucocerebrosidase Activity is Reduced in Cryopreserved Parkinson's Disease Patient Monocytes and Inversely Correlates with Motor Severity

Background:

Reduced activity of lysosomal glucocerebrosidase is found in brain tissue from Parkinson’s disease patients. Glucocerebrosidase is also highly expressed in peripheral blood monocytes where its activity is decreased in Parkinson’s disease patients, even in the absence of GBA mutation.

Objective:

To measure glucocerebrosidase activity in cryopreserved peripheral blood monocytes from 30 Parkinson’s disease patients and 30 matched controls and identify any clinical correlation with disease severity.

Methods:

Flow cytometry was used to measure lysosomal glucocerebrosidase activity in total, classical, intermediate, and non-classical monocytes. All participants underwent neurological examination and motor severity was assessed by the Movement Disorders Society Unified Parkinson’s Disease Rating Scale.

Results:

Glucocerebrosidase activity was significantly reduced in the total and classical monocyte populations from the Parkinson’s disease patients compared to controls. GCase activity in classical monocytes was inversely correlated to motor symptom severity.

Conclusion:

Significant differences in monocyte glucocerebrosidase activity can be detected in Parkinson’s disease patients using cryopreserved mononuclear cells and monocyte GCase activity correlated with motor features of disease. Being able to use cryopreserved cells will facilitate the larger multi-site trials needed to validate monocyte GCase activity as a Parkinson’s disease biomarker.

LRRK2 p.M1646T is associated with glucocerebrosidase activity and with Parkinson's disease

The LRRK2 p.G2019S Parkinson's disease (PD) variant is associated with elevated glucocerebrosidase (GCase) activity in peripheral blood. We aimed to evaluate the association of other LRRK2 variants with PD and its association with GCase activity. LRRK2 and GBA were fully sequenced in 1123 PD patients and 576 controls from the Columbia and PPMI cohorts, in which GCase activity was measured in dried blood spots by liquid chromatography-tandem mass spectrometry. 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 (odds ratio = 1.18, 95% confidence interval = 1.09-1.28, p = 7.33E-05) in 56,306 PD patients and proxy-cases, and 1.4 million controls. 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.

The Mutation Matters: CSF Profiles of GCase, Sphingolipids, α-Synuclein in PDGBA

BACKGROUND

With pathway-specific trials in PD associated with variants in the glucocerebrosidase gene (PD_GBA ) under way, we need markers that confirm the impact of genetic variants in patient-derived biofluids in order to allow patient stratification merely based on genetics and that might serve as biochemical read-out for target engagement.

OBJECTIVE

To explore GBA-pathway-specific biomarker profiles cross-sectionally (TUEPAC-MIGAP, PPMI) and longitudinally (PPMI).

METHODS

We measured enzyme activity of the lysosomal glucocerebrosidase, CSF levels of glucosylceramides (upstream substrate of glucocerebrosidase), CSF levels of ceramides (downstream product of glucocerebrosidase), lactosylceramides, sphingosines, sphingomyelin (by-products) and CSF levels of total α-synuclein in PD_GBA patients compared to PD_{GBA_wildtype} patients.

RESULTS

Cross-sectionally in both cohorts and longitudinally in PPMI: (1) glucocerebrosidase activity was significantly lower in PD_GBA compared to PD_{GBA_wildtype} . (2) CSF levels of upstream substrates (glucosylceramides species) were higher in PD_GBA compared to PD_{GBA_wildtype} . (3) CSF levels of total α-synuclein were lower in PD_GBA compared to PD_{GBA_wildtype} . All of these findings were most pronounced in PD_GBA with severe mutations (PD_{GBA_severe} ). Cross-sectionally in TUEPAC-MIGAP and longitudinally in PPMI, CSF levels of downstream-products (ceramides) were higher in PD_{GBA_severe} . Cross-sectionally in TUEPAC-MIGAP by-products sphinganine and sphingosine-1-phosphate and longitudinally in PPMI species of by-products lactosylceramides and sphingomyelin were higher in PD_{GBA_severe} .

INTERPRETATION

These findings confirm that GBA mutations have a relevant functional impact on biomarker profiles in patients. Bridging the gap between genetics and biochemical profiles now allows patient stratification for clinical trials merely based on mutation status. Importantly, all findings were most prominent in PD_GBA with severe variants. © 2021 International Parkinson and Movement Disorder Society.