Exploring the Genotype-Phenotype Correlation in GBA-Parkinson Disease: Clinical Aspects, Biomarkers, and Potential Modifiers

Refining the clinical diagnosis of Parkinson's disease

Our ability to define, understand, and classify Parkinson's disease (PD) has undergone significant changes since the disorder was first described in 1817. Clinical features and neuropathologic signatures can now be supplemented by in-vivo interrogation of genetic and biological substrates of disease, offering great opportunity for further refining the diagnosis of PD. In this mini-review, we discuss the historical perspectives which shaped our thinking surrounding the definition and diagnosis of PD. We highlight the clinical, genetic, pathologic and biologic diversity which underpins the condition, and proceed to discuss how recent developments in our ability to define biologic and pathologic substrates of disease might impact PD definition, diagnosis, individualised prognostication, and personalised clinical care. We argue that Parkinson's 'disease', as currently diagnosed in the clinic, is actually a syndrome. It is the outward manifestation of any array of potential dysfunctional biologic processes, neuropathological changes, and disease aetiologies, which culminate in common outward clinical features which we term PD; each person has their own unique disease, which we can now define with increasing precision. This is an exciting time in PD research and clinical care. Our ability to refine the clinical diagnosis of PD, incorporating in-vivo assessments of disease biology, neuropathology, and neurogenetics may well herald the era of biologically-based, precision medicine approaches PD management. With this however comes a number of challenges, including how to integrate these technologies into clinical practice in a way which is acceptable to patients, promotes meaningful changes to care, and minimises health economic impact.

Variant-specific effects of GBA1 mutations on dopaminergic neuron proteostasis

Glucocerebrosidase 1 (GBA1) mutations are the most important genetic risk factors for Parkinson's disease (PD). Clinically, mild (e.g., p.N370S) and severe (e.g., p.L444P and p.D409H) GBA1 mutations have different PD phenotypes, with differences in age at disease onset, progression, and the severity of motor and non-motor symptoms. We hypothesize that GBA1 mutations cause the accumulation of α-synuclein by affecting the cross-talk between cellular protein degradation mechanisms, leading to neurodegeneration. Accordingly, we tested whether mild and severe GBA1 mutations differentially affect the degradation of α-synuclein via the ubiquitin-proteasome system (UPS), chaperone-mediated autophagy (CMA), and macroautophagy and differentially cause accumulation and/or release of α-synuclein. Our results demonstrate that endoplasmic reticulum (ER) stress and total ubiquitination rates were significantly increased in cells with severe GBA1 mutations. CMA was found to be defective in induced pluripotent stem cell (iPSC)-derived dopaminergic neurons with mild GBA1 mutations, but not in those with severe GBA1 mutations. When examining macroautophagy, we observed reduced formation of autophagosomes in cells with the N370S and D409H GBA1 mutations and impairments in autophagosome-lysosome fusion in cells with the L444P GBA1 mutation. Accordingly, severe GBA1 mutations were found to trigger the accumulation and release of oligomeric α-synuclein in iPSC-derived dopaminergic neurons, primarily as a result of increased ER stress and defective macroautophagy, while mild GBA1 mutations affected CMA, which is mainly responsible for the degradation of the monomeric form of α-synuclein. Overall, our findings provide new insight into the molecular basis of the clinical variability in PD associated with different GBA1 mutations.

GPNMB Biomarker Levels in GBA1 Carriers with Lewy Body Disorders

BACKGROUND

The GPNMB single-nucleotide polymorphism rs199347 and GBA1 variants both associate with Lewy body disorder (LBD) risk. GPNMB encodes glycoprotein nonmetastatic melanoma protein B (GPNMB), a biomarker for GBA1-associated Gaucher's disease.

OBJECTIVE

The aim of this study was to determine whether GPNMB levels (1) differ in LBD with and without GBA1 variants and (2) associate with rs199347 genotype.

METHODS

We quantified GPNMB levels in plasma and cerebrospinal fluid (CSF) from 124 individuals with LBD with one GBA1 variant (121 plasma, 14 CSF), 631 individuals with LBD without GBA1 variants (626 plasma, 41 CSF), 9 neurologically normal individuals with one GBA1 variant (plasma), and 2 individuals with two GBA1 variants (plasma). We tested for associations between GPNMB levels and rs199347 or GBA1 status.

RESULTS

GPNMB levels associate with rs199347 genotype in plasma (P = 0.022) and CSF (P = 0.007), but not with GBA1 status.

CONCLUSIONS

rs199347 is a protein quantitative trait locus for GPNMB. GPNMB levels are unaltered in individuals carrying one GBA1 variant. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Clinical prediction of GBA carrier status in Parkinson's disease

Introduction

Given the unique natural history of GBA-related Parkinson's disease (GBA-PD) and the potential for novel treatments in this population, genetic testing prioritization for the identification of GBA-PD patients is crucial for prognostication, individualizing treatment, and stratification for clinical trials. Assessing the predictive value of certain clinical traits for the GBA-variant carrier status will help target genetic testing in clinical settings where cost and access limit its availability.

Methods

In-depth clinical characterization through standardized rating scales for motor and non-motor symptoms and self-reported binomial information of a cohort of subjects with PD (n = 100) from our center and from the larger cohort of the Parkinson's Progression Marker Initiative (PPMI) was utilized to evaluate the predictive values of clinical traits for GBA variant carrier status. The model was cross-validated across the two cohorts.

Results

Leveraging non-motor symptoms of PD, we established successful discrimination of GBA variants in the PPMI cohort and study cohort (AUC 0.897 and 0.738, respectively). The PPMI cohort model successfully generalized to the study cohort data using both MDS-UPDRS scores and binomial data (AUC 0.740 and 0.734, respectively) while the study cohort model did not.

Conclusions

We assessed the predictive value of non-motor symptoms of PD for identifying GBA carrier status in the general PD population. These data can be used to determine a simple, clinically oriented model using either the MDS-UPDRS or subjective symptom reporting from patients. Our results can inform patient counseling about the expected carrier risk and test prioritization for the expected identification of GBA variants.

Case-Fatality Rate in Parkinson's Disease: A Nationwide Registry Study

BACKGROUND

Patients with Parkinson's disease (PD) may have an increased risk of mortality, but robust estimates are lacking.

OBJECTIVE

To compare mortality rates nationally between patients with PD and controls.

METHODS

The case-fatality rates of Finnish PD patients diagnosed in 2004-2018 (n = 23,688; 57% male, mean age at diagnosis = 71 years) and randomly selected sex- and age-matched control subjects (n = 94,752) were compared using data from national registries. The median follow-up duration was 5.8 years (max 17 years).

RESULTS

The case-fatality rate in patients with PD was higher than that in matched controls (HR 2.29; 95% CI 2.24-2.33; P < 0.0001). Excess fatality among PD patients was already present at 1 year from diagnosis and then plateaued at 29% at 12 years after diagnosis. The long-term relative hazard of death in PD patients vs. matched controls did not differ based on sex. Patients with early-onset PD (age at diagnosis <50 years old) had the highest relative hazard of death (HR 3.36) compared to matched control subjects, and the relative hazard decreased with higher age at diagnosis. The seven-year excess risk of death decreased during the study period, especially in men. In patients with PD, male sex, increasing age, and increasing comorbidity burden were associated with an increased risk of death.

CONCLUSIONS

An increased risk of death among PD patients was evident from early on. The increase in risk was greatest among young-onset patients. The excess risk in early PD declined during the study period, particularly in men. The reasons for this are unknown.

Analysis of rare Parkinson's disease variants in millions of people

Although many rare variants have been reportedly associated with Parkinson's disease (PD), many have not been replicated or have failed to replicate. Here, we conduct a large-scale replication of rare PD variants. We assessed a total of 27,590 PD cases, 6701 PD proxies, and 3,106,080 controls from three data sets: 23andMe, Inc., UK Biobank, and AMP-PD. Based on well-known PD genes, 834 variants of interest were selected from the ClinVar annotated 23andMe dataset. We performed a meta-analysis using summary statistics of all three studies. The meta-analysis resulted in five significant variants after Bonferroni correction, including variants in GBA1 and LRRK2. Another eight variants are strong candidate variants for their association with PD. Here, we provide the largest rare variant meta-analysis to date, providing information on confirmed and newly identified variants for their association with PD using several large databases. Additionally we also show the complexities of studying rare variants in large-scale cohorts.

Novel beta-glucocerebrosidase chaperone compounds identified from cell-based screening reduce pathologically accumulated glucosylsphingosine in iPS-derived neuronal cells

The beta-glucocerebrosidase (GBA1) gene encodes the lysosomal beta-glucocerebrosidase (GCase) that metabolizes the lipids glucosylceramide (GlcCer) and glucosylsphingosine (GlcSph). Biallelic loss-of-function mutations in GBA1 such as L444P cause Gaucher disease (GD), which is the most prevalent lysosomal storage disease and is histopathologically characterized by abnormal accumulation of the GCase substrates GlcCer and GlcSph. GD with neurological symptoms is associated with severe mutations in the GBA1 gene, most of which cause impairment in the process of GCase trafficking to lysosomes. Given that recombinant GCase protein cannot cross the blood-brain barrier due to its high molecular weight, it is invaluable to develop a brain-penetrant small-molecule pharmacological chaperone as a viable therapeutic strategy to boost GCase activity in the central nervous system. Despite considerable efforts to screen potent GCase activators/chaperones, cell-free assays using recombinant GCase protein have yielded compounds with only marginal efficacy and micromolar EC50 that would not have sufficient clinical efficacy or an acceptable safety margin. Therefore, we utilized a fluorescence-labeled GCase suicide inhibitor, MDW933, to directly monitor lysosomal GCase activity and performed a cell-based screening in fibroblasts from a GD patient with homozygotic L444P mutations. Here, we identified novel compounds that increase the fluorescence signal from labeled GCase with L444P mutations in a dose-dependent manner. Secondary assays using an artificial cell-permeable lysosomal GCase substrate also demonstrated that the identified compounds augment lysosomal GCase L444P in the fibroblast. Moreover, those compounds increased the total GCase L444P protein levels, suggesting the pharmacological chaperone-like mechanism of action. To further elucidate the effect of the compounds on the endogenous GCase substrate GlcSph, we generated iPSC-derived dopaminergic neurons with a GBA1 L444P mutation that exhibit GlcSph accumulation in vitro. Importantly, the identified compounds reduce GlcSph in iPSC-derived dopaminergic neurons with a GBA1 L444P mutation, indicating that the increase in lysosomal GCase resulting from application of the compounds leads to the clearance of pathologically-accumulated GlcSph. Together, our findings pave the way for developing potent and efficacious GCase chaperone compounds as a potential therapeutic approach for neurological GD.

Dopamine pathway and Parkinson's risk variants are associated with levodopa-induced dyskinesia

Background

Levodopa-induced dyskinesia (LID) is a common adverse effect of levodopa, one of the main therapeutics used to treat the motor symptoms of Parkinson's disease (PD). Previous evidence suggests a connection between LID and a disruption of the dopaminergic system as well as genes implicated in PD, including GBA1 and LRRK2.

Objectives

To investigate the effects of genetic variants on risk and time to LID.

Methods

We performed a genome-wide association study (GWAS) and analyses focused on GBA1 and LRRK2 variants. We also calculated polygenic risk scores including risk variants for PD and variants in genes involved in the dopaminergic transmission pathway. To test the influence of genetics on LID risk we used logistic regression, and to examine its impact on time to LID we performed Cox regression including 1,612 PD patients with and 3,175 without LID.

Results

We found that GBA1 variants were associated with LID risk (OR=1.65, 95% CI=1.21-2.26, p=0.0017) and LRRK2 variants with reduced time to LID onset (HR=1.42, 95% CI=1.09-1.84, p=0.0098). The fourth quartile of the PD PRS was associated with increased LID risk (ORfourth_quartile=1.27, 95% CI=1.03-1.56, p=0.0210). The third and fourth dopamine pathway PRS quartiles were associated with a reduced time to development of LID (HRthird_quartile=1.38, 95% CI=1.07-1.79, p=0.0128; HRfourth_quartile=1.38, 95% CI=1.06-1.78, p=0.0147).

Conclusions

This study suggests that variants implicated in PD and in the dopaminergic transmission pathway play a role in the risk/time to develop LID. Further studies will be necessary to examine how these findings can inform clinical care.

Mutational spectrum and clinical features of GBA1 variants in a Chinese cohort with Parkinson's disease

GBA1 variants are important risk factors for Parkinson's disease (PD). Most studies assessing GBA1-related PD risk have been performed in European-derived populations. Although the coding region of the GBA1 gene in the Chinese population has been analyzed, the sample sizes were not adequate. In this study, we aimed to investigate GBA1 variants in a large Chinese cohort of patients with PD and healthy control and explore the associated clinical characteristics. GBA1 variants in 4034 patients and 2931 control participants were investigated using whole-exome and whole-genome sequencing. The clinical features of patients were evaluated using several scales. Regression analysis, chi-square, and Fisher exact tests were used to analyze GBA1 variants and the clinical symptoms of different groups. We identified 104 variants, including 8 novel variants, expanding the spectrum of GBA1 variants. The frequency of GBA1 variants in patients with PD was 7.46%, higher than that in the control (1.81%) (P < 0.001, odds ratio [OR] = 4.38, 95% confidence interval [CI]: 3.26-5.89). Among patients, 176 (4.36%) had severe variants, 34 (0.84%) carried mild variants, three (0.07%) had risk variants, and 88 (2.18%) carried unknown variants. Our study, for the first time, found that p.G241R (P = 0.007, OR = 15.3, 95% CI: 1.25-261.1) and p.S310G (P = 0.005, OR = 4.86, 95% CI: 1.52-28.04) variants increased the risk of PD. Patients with GBA1 variants exhibited an earlier onset age and higher risk of probable rapid-eye-movement sleep behavior disorder, olfactory dysfunction, depression, and autonomic dysfunction than patients without GBA1 variants.

Leveraging genetic diversity to understand monogenic Parkinson's disease's landscape in AfrAbia

Parkinson's disease may be caused by a single highly deleterious and penetrant pathogenic variant in 5-10% of cases (monogenic). Research into these mutational disorders yields important pathophysiological insights. This article examines the phenotype, genotype, pathophysiology, and geographic and ethnic distribution of genetic forms of disease. Well established Parkinson's disease (PD) causal variants can follow an autosomal dominant (SNCA, LRRK2, and VPS35) and autosomal recessive pattern of inheritance (PRKN, PINK1, and DJ). Parkinson's disease is a worldwide condition, yet the AfrAbia population is understudied in this regard. No prevalence or incidence investigations have been conducted yet. Few studies on genetic risk factors for PD in AfrAbia communities have been reported which supported the notion that the prevalence and incidence rates of PD in AfrAbia are generally lower than those reported for European and North American populations. There have been only a handful of documented genetic studies of PD in AfrAbia and very limited cohort and case-control research studies on PD have been documented. In this article, we provide a summary of prior conducted research on monogenic PD in Africa and highlight data gaps and promising new research directions. We emphasize that monogenic Parkinson's disease is influenced by distinctions in ethnicity and geography, thereby reinforcing the need for global initiatives to aggregate large numbers of patients and identify novel candidate genes. The current article increases our knowledge of the genetics of Parkinson's disease (PD) and helps to further our knowledge on the genetic factors that contribute to PD, such as the lower penetrance and varying clinical expressivity of known genetic variants, particularly in AfrAbian PD patients.

Sex differences in alpha-synucleinopathies: a systematic review

Background

Past research indicates a higher prevalence, incidence, and severe clinical manifestations of alpha-synucleinopathies in men, leading to a suggestion of neuroprotective properties of female sex hormones (especially estrogen). The potential pathomechanisms of any such effect on alpha-synucleinopathies, however, are far from understood. With that aim, we undertook to systematically review, and to critically assess, contemporary evidence on sex and gender differences in alpha-synucleinopathies using a bench-to-bedside approach.

Methods

In this systematic review, studies investigating sex and gender differences in alpha-synucleinopathies (Rapid Eye Movement (REM) Behavior Disorder (RBD), Parkinson's Disease (PD), Dementia with Lewy Bodies (DLB), Multiple System Atrophy (MSA)) from 2012 to 2022 were identified using electronic database searches of PubMed, Embase and Ovid.

Results

One hundred sixty-two studies were included; 5 RBD, 6 MSA, 20 DLB and 131 PD studies. Overall, there is conclusive evidence to suggest sex-and gender-specific manifestation in demographics, biomarkers, genetics, clinical features, interventions, and quality of life in alpha-synucleinopathies. Only limited data exists on the effects of distinct sex hormones, with majority of studies concentrating on estrogen and its speculated neuroprotective effects.

Conclusion

Future studies disentangling the underlying sex-specific mechanisms of alpha-synucleinopathies are urgently needed in order to enable novel sex-specific therapeutics.

Recent Advances in the Treatment of Genetic Forms of Parkinson's Disease: Hype or Hope?

Parkinson's disease (PD) is a multifarious neurodegenerative disease. Its pathology is characterized by a prominent early death of dopaminergic neurons in the pars compacta of the substantia nigra and the presence of Lewy bodies with aggregated α-synuclein. Although the α-synuclein pathological aggregation and propagation, induced by several factors, is considered one of the most relevant hypotheses, PD pathogenesis is still a matter of debate. Indeed, environmental factors and genetic predisposition play an important role in PD. Mutations associated with a high risk for PD, usually called monogenic PD, underlie 5% to 10% of all PD cases. However, this percentage tends to increase over time because of the continuous identification of new genes associated with PD. The identification of genetic variants that can cause or increase the risk of PD has also given researchers the possibility to explore new personalized therapies. In this narrative review, we discuss the recent advances in the treatment of genetic forms of PD, focusing on different pathophysiologic aspects and ongoing clinical trials.

How should future clinical trials be designed in the search for disease-modifying therapies for Parkinson's disease?

INTRODUCTION

Although there has been substantial progress in research and innovations in symptomatic treatments, similar success has not been achieved in disease-modifying therapy (DMT) for Parkinson's disease (PD). Considering the enormous motor, psychosocial and financial burden associated with PD, safe and effective DMT is of paramount importance.

AREAS COVERED

One of the reasons for the lack of progress in DMT for PD is poor or inappropriate design of clinical trials. In the first part of the article, the authors focus on the plausible reasons why the previous trials have failed and in the latter part, they provide their perspectives on future DMT trials.

EXPERT OPINION

There are several potential reasons why previous trials have failed, including broad clinical and etiopathogenic heterogeneity of PD, poor definition and documentation of target engagement, lack of appropriate biomarkers and outcome measures, and short duration of follow-up. To address these deficiencies, future trials may consider- (i) a more customized approach to select the most suitable participants and therapeutic approaches, (ii) explore combination therapies that would target multiple pathogenetic mechanisms, and (iii) moving beyond targeting only motor symptoms to also assessing non-motor features of PD in well-designed longitudinal studies.

Motor and non-motor features in Parkinson's Disease patients carrying GBA gene mutations

BACKGROUND

Mutations of the Glucocerebrosidase (GBA) gene are the most common genetic risk factor yet discovered for Parkinson's Disease (PD), being found in about 5-14% of Caucasian patients.

OBJECTIVE

We aimed to assess motor and non-motor symptoms (NMS) in patients with GBA-related PD (GBA-PD) in comparison with idiopathic PD (iPD) subjects using standardized and validated scales.

METHODS

Eleven (4 M, 7 F) patients with GBA-PD and 22 iPD patients, selected from the same cohort and matched for gender, age, and disease duration, were enrolled. The disease severity was assessed by Unified Parkinson's Disease Rating Scale-section III, gait disorder and falls by Freezing of Gait Questionnaire, and motor fluctuations by Wearing off questionnaire. NMS were evaluated using the following scales: Mini-Mental State Examination and extended neuropsychological battery, if required, Non-Motor Symptoms Scale, SCOPA-AUT Questionnaire, Apathy Evaluation Scale, Beck Depression Inventory, Epworth Sleepiness Scale, Restless Legs Syndrome Rating Scale, REM Sleep Behavior Disorder Screening Questionnaire, and Questionnaire for Impulsive-Compulsive Disorders in Parkinson's disease.

RESULTS

GBA-PD patients showed a more severe and rapidly progressive disease, and more frequent positive family history for PD, akinetic-rigid phenotype, postural instability, dementia, and psychosis in comparison to iPD. Two of three subjects carrying L444P mutation presented with early dementia. We also found a higher occurrence of fatigue, diurnal sleepiness, and intolerance to heat/cold in the carriers group.

CONCLUSIONS

Our results confirm that NMS and a more severe and faster disease course more frequently occur among GBA-PD patients in comparison to iPD.

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.

[Analysis of GBA mutations in patients with Parkinson's disease in the Krasnoyarsk region]

OBJECTIVE

To analyze mutations and polymorphisms in exons 2, 7, 8, 9, 10 and 11 of the glucocerebrosidase (GBA) gene in patients of the Krasnoyarsk region diagnosed with Parkinson's disease (PD).

MATERIAL AND METHODS

Seventy-five patients with sporadic and familial forms of PD were examined. Genomic DNA was isolated from the whole blood of patients. The above mentioned exons of GBA were analyzed using Sanger sequencing.

RESULTS

Various changes in the DNA structure of GBA were detected in 11 patients, thus, the overall frequency of variants was 14.7%, and the frequency of pathologically significant mutations (p.L444P, p.D409H, p.H255Q) was 5.3%.

CONCLUSION

The frequencies of variants in GBA, one of the most common high-risk factors for PD, in patients of the Krasnoyarsk region turned out to be quite high and comparable to that in patients in other populations of the world. Thus, screening for GBA mutations is relevant for PD patients living in the Krasnoyarsk region as part of genetic counseling at present, and in the future it may be necessary for personalized treatment.

Anderson-Fabry Disease: A New Piece of the Lysosomal Puzzle in Parkinson Disease?

Anderson-Fabry disease (AFD) is an inherited lysosomal storage disorder characterized by a composite and multisystemic clinical phenotype and frequent involvement of the central nervous system (CNS). Research in this area has largely focused on the cerebrovascular manifestations of the disease, and very little has been described about further neurological manifestations, which are known in other lysosomal diseases, such as Gaucher disease. In particular, a clinical and neuroimaging phenotype suggesting neurodegeneration as a putative mechanism has never been fully described for AFD, but the increased survival of affected patients with early diagnosis and the possibility of treatment have given rise to some isolated reports in the literature on the association of AFD with a clinical phenotype of Parkinson disease (PD). The data are currently scarce, but it is possible to hypothesize the molecular mechanisms of cell damage that support this association; this topic is worthy of further study in particular in relation to the therapeutic possibilities, which have significantly modified the natural history of the disease but which are not specifically dedicated to the CNS. In this review, the molecular mechanisms underlying this association will be proposed, and the available data with implications for future research and treatment will be rewritten.

Subtyping of early-onset Parkinson's disease using cluster analysis: A large cohort study

BACKGROUND

Increasing evidence suggests that early-onset Parkinson's disease (EOPD) is heterogeneous in its clinical presentation and progression. Defining subtypes of EOPD is needed to better understand underlying mechanisms, predict disease course, and eventually design more efficient personalized management strategies.

OBJECTIVE

To identify clinical subtypes of EOPD, assess the clinical characteristics of each EOPD subtype, and compare the progression between EOPD subtypes.

MATERIALS AND METHODS

A total of 1,217 patients were enrolled from a large EOPD cohort of the Parkinson's Disease & Movement Disorders Multicenter Database and Collaborative Network in China (PD-MDCNC) between January 2017 and September 2021. A comprehensive spectrum of motor and non-motor features were assessed at baseline. Cluster analysis was performed using data on demographics, motor symptoms and signs, and other non-motor manifestations. In 454 out of total patients were reassessed after a mean follow-up time of 1.5 years to compare progression between different subtypes.

RESULTS

Three subtypes were defined: mild motor and non-motor dysfunction/slow progression, intermediate and severe motor and non-motor dysfunction/malignant. Compared to patients with mild subtype, patients with the severe subtype were more likely to have rapid eye movement sleep behavior disorder, wearing-off, and dyskinesia, after adjusting for age and disease duration at baseline, and showed a more rapid progression in Unified Parkinson's Disease Rating Scale (UPDRS) total score (P = 0.002), UPDRS part II (P = 0.014), and III (P = 0.001) scores, Hoehn and Yahr stage (P = 0.001), and Parkinson's disease questionnaire-39 item version score (P = 0.012) at prospective follow-up.

CONCLUSION

We identified three different clinical subtypes (mild, intermediate, and severe) using cluster analysis in a large EOPD cohort for the first time, which is important for tailoring therapy to individuals with EOPD.

A multicenter study of genetic testing for Parkinson’s disease in the clinical setting

Parkinson’s disease (PD) guidelines lack clear criteria for genetic evaluation. We assessed the yield and rationale of genetic testing for PD in a routine clinical setting on a multicenter cohort of 149 early-onset and familial patients by exome sequencing and semi-quantitative multiplex ligation-dependent probe amplification of evidence-based PD-associated gene panel. We show that genetic testing for PD should be considered for both early-onset and familial patients alike, and a clinical yield of about 10% in the Caucasian population can be expected.

Genetic architecture of Parkinson’s disease subtypes – Review of the literature

The heterogeneity of Parkinson’s disease (PD) has been recognized since its description by James Parkinson over 200 years ago. The complexity of motor and non-motor PD manifestations has led to many attempts of PD subtyping with different prognostic outcomes; however, the pathophysiological foundations of PD heterogeneity remain elusive. Genetic contributions to PD may be informative in understanding the underpinnings of PD subtypes. As such, recognizing genotype-phenotype associations may be crucial for successful gene therapy. We review the state of knowledge on the genetic architecture underlying PD subtypes, discussing the monogenic forms, as well as oligo- and polygenic risk factors associated with various PD subtypes. Based on our review, we argue for the unification of PD subtyping classifications, the dichotomy of studies on genetic factors and genetic modifiers of PD, and replication of results from previous studies.

Serum Phospholipid Profile Changes in Gaucher Disease and Parkinson's Disease

Alterations in the levels of serum sphingolipids and phospholipids have been reported in Gaucher disease and in Parkinson's disease, suggesting a potential role of these lipids as biomarkers. This project's objective is to detect novel associations and novel candidate biomarkers in the largest Spanish Gaucher and Parkinson diseases of the Iberian Peninsula. For that, 278 participants were included: 100 sporadic Parkinson's patients, 70 Gaucher patients, 15 GBA1-mutation-carrier Parkinson's patients and 93 controls. A serum lipidomics array including 10 phospholipid groups, 368 species, was performed using high-performance liquid chromatography-mass spectrometry. Lipid levels were compared between groups via multiple-regression analyses controlling for clinical and demographic parameters. Additionally, lipid levels were compared within the Gaucher and Parkinson's groups controlling for medication and/or disease severity. Results were controlled for robustness by filtering of non-detectable lipid values. There was an increase in the levels of phosphatidylcholine, with a simultaneous decrease in lyso-phosphatidylcholine, in the Gaucher, Parkinson's and GBA1-mutation-carrier Parkinson's patients vs. controls. Phosphatidylethanolamine, lyso- and plasmalogen-phosphatidylethanolamine were also increased in Gaucher and Parkinson's. Gaucher patients also showed an increase in lyso-phosphatidylserine and phosphatidylglycerol. While in the Gaucher and Parkinson's groups, velaglucerase alpha and dopamine agonists, respectively, showed positive associations with the lipid changes, miglustat treatment in Gaucher patients normalized the altered phosphatidylcholine/lyso-phosphatidylcholine ratio. In conclusion, Gaucher and Parkinson's patients showed changes in various serum phospholipid levels when compared with healthy controls, further supporting the role of such lipids in disease development and, possibly, as putative biomarkers. This hypothesis was reinforced by the normalizing effect of miglustat, and by controlling for data robustness, even though the limited number of participants, especially in the sub-distribution by treatment groups in GD requires validation in a larger number of patients.

Genetics of validated Parkinson's disease subtypes in the Oxford Discovery and Tracking Parkinson's cohorts

OBJECTIVES

To explore the genetics of four Parkinson's disease (PD) subtypes that have been previously described in two large cohorts of patients with recently diagnosed PD. These subtypes came from a data-driven cluster analysis of phenotypic variables.

METHODS

We looked at the frequency of genetic mutations in glucocerebrosidase (GBA) and leucine-rich repeat kinase 2 against our subtypes. Then we calculated Genetic Risk Scores (GRS) for PD, multiple system atrophy, progressive supranuclear palsy, Lewy body dementia, and Alzheimer's disease. These GRSs were regressed against the probability of belonging to a subtype in the two independent cohorts and we calculated q-values as an adjustment for multiple testing across four subtypes. We also carried out a Genome-Wide Association Study (GWAS) of belonging to a subtype.

RESULTS

A severe disease subtype had the highest rates of patients carrying GBA mutations while the mild disease subtype had the lowest rates (p=0.009). Using the GRS, we found a severe disease subtype had a reduced genetic risk of PD (p=0.004 and q=0.015). In our GWAS no individual variants met genome wide significance (<5×10e-8) although four variants require further follow-up, meeting a threshold of <1×10e-6.

CONCLUSIONS

We have found that four previously defined PD subtypes have different genetic determinants which will help to inform future studies looking at underlying disease mechanisms and pathogenesis in these different subtypes of disease.

Cognition as a mediator for gait and balance impairments in GBA-related Parkinson's disease

The extent to which the heterogeneity of gait and balance problems in PD may be explained by genetic variation is unknown. Variants in the glucocerebrosidase (GBA) gene are the strongest known genetic risk factor for PD and are associated with greater motor and cognitive severity. However, the impact of GBA variants on comprehensive measures of gait and balance and their relationship to cognition remains unknown. We aimed to determine differences in gait and balance impairments in those with and without GBA variants (mutation carriers and E326K polymorphism) and explore direct and indirect effects of GBA status on gait, balance, and cognition. 332 participants, 43 of whom had GBA variants, were recruited. Participants completed a comprehensive, objective assessment of gait and standing balance using body-worn inertial sensors. Group differences in gait and balance between PD with and without GBA variants were assessed with linear regression, adjusting for age, gender, clinical testing site, disease duration, and apolipoprotein E (APOE) ɛ4 status. Structural equation modeling (SEM) explored direct relationships between GBA status and gait and balance and indirect relationships between GBA status and gait and balance via cognition. The GBA variant group had more impaired gait (pace and variability) and balance (sway area/jerk and sway velocity), than the non-GBA variant group. SEM demonstrated cognition as a mediator of GBA status on gait and balance. The close relationships among GBA, gait/balance, and cognition suggest potential for novel therapeutics to target the GBA pathway and/or cognition to improve mobility in PD GBA variants.

Role of Lysosomal Gene Variants in Modulating GBA-Associated Parkinson's Disease Risk

BACKGROUND

To date, variants in the GBA gene represent the most frequent large-effect genetic factor associated with Parkinson's disease (PD). However, the reason why individuals with the same GBA variant may or may not develop neurodegeneration and PD is still unclear.

OBJECTIVES

Therefore, we evaluated the contribution of rare variants in genes responsible for lysosomal storage disorders (LSDs) to GBA-PD risk, comparing the burden of deleterious variants in LSD genes in PD patients versus asymptomatic subjects, all carriers of deleterious variants in GBA.

METHODS

We used a custom next-generation sequencing panel, including 50 LSD genes, to screen 305 patients and 207 controls (discovery cohort). Replication and meta-analysis were performed in two replication cohorts of GBA-variant carriers, of 250 patients and 287 controls, for whom exome or genome data were available.

RESULTS

Statistical analysis in the discovery cohort revealed a significantly increased burden of deleterious variants in LSD genes in patients (P = 0.0029). Moreover, our analyses evidenced that the two strongest modifiers of GBA penetrance are a second variation in GBA (5.6% vs. 1.4%, P = 0.023) and variants in genes causing mucopolysaccharidoses (6.9% vs. 1%, P = 0.0020). These results were confirmed in the meta-analysis, where we observed pooled odds ratios of 1.42 (95% confidence interval [CI] = 1.10-1.83, P = 0.0063), 4.36 (95% CI = 2.02-9.45, P = 0.00019), and 1.83 (95% CI = 1.04-3.22, P = 0.038) for variants in LSD genes, GBA, and mucopolysaccharidosis genes, respectively.

CONCLUSION

The identification of genetic lesions in lysosomal genes increasing PD risk may have important implications in terms of patient stratification for future therapeutic trials. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson Movement Disorder Society.

Genetic heterogeneity on sleep disorders in Parkinson's disease: a systematic review and meta-analysis

A growing amount of evidence has indicated contributions of variants in causative genes of Parkinson’s disease (PD) to the development of sleep disturbance in PD and prodromal PD stages. In this article, we aimed to investigate the role of genetics in sleep disorders in PD patients and asymptomatic carriers at prodromal stage of PD. A systematic review and meta-analysis of observational studies was conducted based on the MEDLINE, EMBASE and PsychINFO databases. A pooled effect size was calculated by odds ratio (OR) and standard mean difference (SMD). Forty studies were selected for quantitative analysis, including 17 studies on glucocerebrosidase (GBA), 25 studies on Leucine-rich repeat kinase 2 (LRRK2) and 7 on parkin (PRKN) genes, and 3 studies on alpha-synuclein gene (SNCA) were used for qualitative analysis. Patients with PD carrying GBA variants had a significantly higher risk for rapid-eye-movement behavior disorders (RBD) (OR, 1.82) and higher RBD Screening Questionnaire scores (SMD, 0.33). Asymptomatic carriers of GBA variants had higher severity of RBD during follow-up. Patients with PD carrying the LRRK2 G2019S variant had lower risk and severity of RBD compared with those without LRRK2 G2019S. Variants of GBA, LRRK2 and PRKN did not increase or decrease the risk and severity of excessive daytime sleepiness and restless legs syndrome in PD. Our findings suggest that the genetic heterogeneity plays a role in the development of sleep disorders, mainly RBD, in PD and the prodromal stage of PD.

Prevalence and Genotype-Phenotype Correlations of GBA-Related Parkinson's Disease in a Large Chinese Cohort

Background and purpose

Variants in the glucocerebrosidase (GBA) gene are recognized as a common and important genetic risk factor for Parkinson disease (PD). However, the impact of variant severity on the clinical phenotype of PD in the Chinese population remains unclear. Thus, the present study aimed to determine the frequency of GBA‐related PD (GBA‐PD) and the relationship of GBA variant severity with clinical characteristics in a large Chinese cohort.

Methods

Long‐range polymerase chain reaction and next generation sequencing were performed for the entire GBA gene. GBA variant severity was classified into five classes: mild, severe, risk, complex, and unknown.

Results

Among the total 737 PD patients, 47 GBA variants were detected in 79 (10.72%) patients, and the most common GBA variants were R163Q, L444P, and R120W. Complete demographic and clinical data were obtained for 673 patients, which revealed that 18.50% of early onset PD patients had GBA variants. Compared with patients without GBA variants, GBA‐PD patients experienced PD onset an average of 4 years earlier and had more severe motor and nonmotor symptoms. Patients carrying severe and complex variants had a higher burden of nonmotor symptoms, especially depression, and more mood/cognitive and gastrointestinal symptoms than patients carrying mild variants.

Conclusions

GBA‐PD is highly prevalent in the Chinese population. The severity of GBA variants underlies distinct phenotypic spectrums, with PD patients carrying severe and complex variants seeming to have similar phenotypes. PD patient stratification by GBA variant severity should become a prerequisite for selecting specific treatments.