Complete screening for glucocerebrosidase mutations in Parkinson disease patients from Portugal

GBA1 in Parkinson's disease: variant detection and pathogenicity scoring matters

BACKGROUND

GBA1 variants are the strongest genetic risk factor for Parkinson's disease (PD). However, the pathogenicity of GBA1 variants concerning PD is still not fully understood. Additionally, the frequency of GBA1 variants varies widely across populations.

OBJECTIVES

To evaluate Oxford Nanopore sequencing as a strategy, to determine the frequency of GBA1 variants in Norwegian PD patients and controls, and to review the current literature on newly identified variants that add to pathogenicity determination.

METHODS

We included 462 Norwegian PD patients and 367 healthy controls. We sequenced the full-length GBA1 gene on the Oxford Nanopore GridION as an 8.9 kb amplicon. Six analysis pipelines were compared using two aligners (NGMLR, Minimap2) and three variant callers (BCFtools, Clair3, Pepper-Margin-Deepvariant). Confirmation of GBA1 variants was performed by Sanger sequencing and the pathogenicity of variants was evaluated.

RESULTS

We found 95.8% (115/120) true-positive GBA1 variant calls, while 4.2% (5/120) variant calls were false-positive, with the NGMLR/Minimap2-BCFtools pipeline performing best. In total, 13 rare GBA1 variants were detected: two were predicted to be (likely) pathogenic and eleven were of uncertain significance. The odds of carrying one of the two common GBA1 variants, p.L483P or p.N409S, in PD patients were estimated to be 4.11 times the odds of carrying one of these variants in controls (OR = 4.11 [1.39, 12.12]).

CONCLUSIONS

In conclusion, we have demonstrated that Oxford long-read Nanopore sequencing, along with the NGMLR/Minimap2-BCFtools pipeline is an effective tool to investigate GBA1 variants. Further studies on the pathogenicity of GBA1 variants are needed to assess their effect on PD.

Alpha-Synuclein mRNA Level Found Dependent on L444P Variant in Carriers and Gaucher Disease Patients on Enzyme Replacement Therapy

Gaucher disease (GD) is the most frequent sphingolipidosis, caused by biallelic pathogenic variants in the GBA1 gene encoding for β-glucocerebrosidase (GCase, E.C. 3.2.1.45). The condition is characterized by hepatosplenomegaly, hematological abnormalities, and bone disease in both non-neuronopathic type 1 (GD1) and neuronopathic type 3 (GD3). Interestingly, GBA1 variants were found to be one of the most important risk factors for the development of Parkinson's disease (PD) in GD1 patients. We performed a comprehensive study regarding the two most disease-specific biomarkers, glucosylsphingosine (Lyso-Gb1) and α-synuclein for GD and PD, respectively. A total of 65 patients with GD treated with ERT (47 GD1 patients and 18 GD3 patients), 19 GBA1 pathogenic variant carriers (including 10 L444P carriers), and 16 healthy subjects were involved in the study. Lyso-Gb1 was assessed by dried blood spot testing. The level of α-synuclein as an mRNA transcript, total, and oligomer protein concentration were measured with real-time PCR and ELISA, respectively. α-synuclein mRNA level was found significantly elevated in GD3 patients and L444P carriers. GD1 patients, along with GBA1 carriers of an unknown or unconfirmed variant, as well as healthy controls, have the same low level of α-synuclein mRNA. There was no correlation found between the level of α-synuclein mRNA and age in GD patients treated with ERT, whereas there was a positive correlation in L444P carriers.

The genetic basis of multiple system atrophy

Multiple system atrophy (MSA) is a heterogenous, uniformly fatal neurodegenerative ɑ-synucleinopathy. Patients present with varying degrees of dysautonomia, parkinsonism, cerebellar dysfunction, and corticospinal degeneration. The underlying pathophysiology is postulated to arise from aberrant ɑ-synuclein deposition, mitochondrial dysfunction, oxidative stress and neuroinflammation. Although MSA is regarded as a primarily sporadic disease, there is a possible genetic component that is poorly understood. This review summarizes current literature on genetic risk factors and potential pathogenic genes and loci linked to both sporadic and familial MSA, and underlines the biological mechanisms that support the role of genetics in MSA. We discuss a broad range of genes that have been associated with MSA including genes related to Parkinson's disease (PD), oxidative stress, inflammation, and tandem gene repeat expansions, among several others. Furthermore, we highlight various genetic polymorphisms that modulate MSA risk, including complex gene-gene and gene-environment interactions, which influence the disease phenotype and have clinical significance in both presentation and prognosis. Deciphering the exact mechanism of how MSA can result from genetic aberrations in both experimental and clinical models will facilitate the identification of novel pathophysiologic clues, and pave the way for translational research into the development of disease-modifying therapeutic targets.

Glucocerebrosidase mutations: A paradigm for neurodegeneration pathways

Biallelic (homozygous or compound heterozygous) glucocerebrosidase gene (GBA) mutations cause Gaucher disease, whereas heterozygous mutations are numerically the most important genetic risk factor for Parkinson disease (PD) and are associated with the development of other synucleinopathies, notably Dementia with Lewy Bodies. This phenomenon is not limited to GBA, with converging evidence highlighting further examples of autosomal recessive disease genes increasing neurodegeneration risk in heterozygous mutation carriers. Nevertheless, despite extensive research, the cellular mechanisms by which mutations in GBA, encoding lysosomal enzyme β-glucocerebrosidase (GCase), predispose to neurodegeneration remain incompletely understood. Alpha-synuclein (A-SYN) accumulation, autophagic lysosomal dysfunction, mitochondrial abnormalities, ER stress and neuroinflammation have been proposed as candidate pathogenic pathways in GBA-linked PD. The observation of GCase and A-SYN interactions in PD initiated the development and evaluation of GCase-targeted therapeutics in PD clinical trials.

Recalling the pathology of Parkinson's disease; lacking exact figure of prevalence and genetic evidence in Asia with an alarming outcome: A time to step-up

Parkinson's disease (PD) is the second most common and progressive neurodegenerative disease globally, with major symptoms like bradykinesia, impaired posture, and tremor. Several genetic and environmental factors have been identified but elucidating the main factors have been challenging due to the disease's complex nature. Diagnosis, prognosis, and management of such diseases are challenging and require effective targeted attention in developing countries. Recently, PD is growing rapidly in many crowded Asian countries as an alarming threat with inadequate knowledge of its prevalence, genetic architecture, and geographic distribution. This study gave an in-depth overview of the prevalence, incidence and genomic/genetics studies published so far in the Asian population. To the best of our knowledge, PD has increased significantly in several Asian countries, including China, South Korea, Japan, Thailand, and Israel over the past few years, requiring a greater level of care and attention. Genetic screening of families with PD at national levels and establishing an official database of PD cases are essential to get a comprehensive and conclusive view of the exact prevalence and genetic diversity of PD in the Asian population to properly manage and treat the disease.

Parkinson's Disease Associated with GBA Gene Mutations: Molecular Aspects and Potential Treatment Approaches

Parkinson's disease (PD) is a multifactorial neurodegenerative disease. To date, genome-wide association studies have identified more than 70 loci associated with the risk of PD. Variants in the GBA gene encoding glucocerebrosidase are quite often found in PD patients in all populations across the world, which justifies intensive investigation of this gene. A number of biochemical features have been identified in patients with GBA-associated Parkinson's disease (GBA-PD). In particular, these include decreased activity of glucocerebrosidase and accumulation of the glucosylceramide substrate. These features were the basis for putting forward a hypothesis about treatment of GBA-PD using new strategies aimed at restoring glucocerebrosidase activity and reducing the substrate concentration. This paper discusses the molecular and genetic mechanisms of GBA-PD pathogenesis and potential approaches to the treatment of this form of the disease.

Recent developments in the treatment of Parkinson's Disease

Parkinson's disease (PD) is a common neurodegenerative disease typified by a movement disorder consisting of bradykinesia, rest tremor, rigidity, and postural instability. Treatment options for PD are limited, with most of the current approaches based on restoration of dopaminergic tone in the striatum. However, these do not alter disease course and do not treat the non-dopamine-dependent features of PD such as freezing of gait, cognitive impairment, and other non-motor features of the disorder, which often have the greatest impact on quality of life. As understanding of PD pathogenesis grows, novel therapeutic avenues are emerging. These include treatments that aim to control the symptoms of PD without the problematic side effects seen with currently available treatments and those that are aimed towards slowing pathology, reducing neuronal loss, and attenuating disease course. In this latter regard, there has been much interest in drug repurposing (the use of established drugs for a new indication), with many drugs being reported to affect PD-relevant intracellular processes. This approach offers an expedited route to the clinic, given that pharmacokinetic and safety data are potentially already available. In terms of better symptomatic therapies that are also regenerative, gene therapies and cell-based treatments are beginning to enter clinical trials, and developments in other neurosurgical strategies such as more nuanced deep brain stimulation approaches mean that the landscape of PD treatment is likely to evolve considerably over the coming years. In this review, we provide an overview of the novel therapeutic approaches that are close to, or are already in, clinical trials.

GBA-Related Parkinson's Disease: Dissection of Genotype-Phenotype Correlates in a Large Italian Cohort

BACKGROUND

Variants in GBA are the most common genetic risk factor for Parkinson's disease (PD). The impact of different variants on the PD clinical spectrum is still unclear.

OBJECTIVES

We determined the frequency of GBA-related PD in Italy and correlated GBA variants with motor and nonmotor features and their occurrence over time.

METHODS

Sanger sequencing of the whole GBA gene was performed. Variants were classified as mild, severe, complex, and risk. β-glucocerebrosidase activity was measured. The Kaplan-Meier method and Cox proportional hazard regression models were performed.

RESULTS

Among 874 patients with PD, 36 variants were detected in 14.3%, including 20.4% early onset. Patients with GBA-PD had earlier and more frequent occurrence of several nonmotor symptoms. Patients with severe and complex GBA-PD had the highest burden of symptoms and a higher risk of hallucinations and cognitive impairment. Complex GBA-PD had the lowest β-glucocerebrosidase activity.

CONCLUSIONS

GBA-PD is highly prevalent in Italy. Different types of mutations underlie distinct phenotypic profiles. © 2020 International Parkinson and Movement Disorder Society.

A Large-Scale Full GBA1 Gene Screening in Parkinson's Disease in the Netherlands

BACKGROUND

The most common genetic risk factor for Parkinson's disease known is a damaging variant in the GBA1 gene. The entire GBA1 gene has rarely been studied in a large cohort from a single population. The objective of this study was to assess the entire GBA1 gene in Parkinson's disease from a single large population.

METHODS

The GBA1 gene was assessed in 3402 Dutch Parkinson's disease patients using next-generation sequencing. Frequencies were compared with Dutch controls (n = 655). Family history of Parkinson's disease was compared in carriers and noncarriers.

RESULTS

Fifteen percent of patients had a GBA1 nonsynonymous variant (including missense, frameshift, and recombinant alleles), compared with 6.4% of controls (OR, 2.6; P < 0.001). Eighteen novel variants were detected. Variants previously associated with Gaucher's disease were identified in 5.0% of patients compared with 1.5% of controls (OR, 3.4; P < 0.001). The rarely reported complex allele p.D140H + p.E326K appears to likely be a Dutch founder variant, found in 2.4% of patients and 0.9% of controls (OR, 2.7; P = 0.012). The number of first-degree relatives (excluding children) with Parkinson's disease was higher in p.D140H + p.E326K carriers (5.6%, 21 of 376) compared with p.E326K carriers (2.9%, 29 of 1014); OR, 2.0; P = 0.022, suggestive of a dose effect for different GBA1 variants.

CONCLUSIONS

Dutch Parkinson's disease patients display one of the largest frequencies of GBA1 variants reported so far, consisting in large part of the mild p.E326K variant and the more severe Dutch p.D140H + p.E326K founder allele. © 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC. on behalf of International Parkinson and Movement Disorder Society.

Impact of GBA1 variants on long-term clinical progression and mortality in incident Parkinson's disease

INTRODUCTION

Variants in the GBA1 gene have been identified as a common risk factor for Parkinson's disease (PD). In addition to pathogenic mutations (those associated with Gaucher disease), a number of 'non-pathogenic' variants also occur at increased frequency in PD. Previous studies have reported that pathogenic variants adversely affect the clinical course of PD. The role of 'non-pathogenic' GBA1 variants on PD course is less clear. In this study, we report the effect of GBA1 variants in incident PD patients with long-term follow-up.

METHODS

The study population consisted of patients in the Cambridgeshire Incidence of Parkinson's disease from General Practice to Neurologist and Parkinsonism: Incidence, Cognition and Non-motor heterogeneity in Cambridgeshire cohorts. Patients were grouped into non-carriers, carriers of 'non-pathogenic' GBA1 variants and carriers of pathogenic GBA1 mutations. Survival analyses for time to development of dementia, postural instability and death were carried out. Cox regression analysis controlling for potential confounders were used to determine the impact of GBA1 variants on these outcome measures.

RESULTS

GBA1 variants were identified in 14.4% of patients. Pathogenic and 'non-pathogenic' GBA1 variants were associated with the accelerated development of dementia and a more aggressive motor course. Pathogenic GBA1 variants were associated with earlier mortality in comparison with non-carriers, independent of the development of dementia.

DISCUSSION

GBA1 variants, including those not associated with Gaucher disease, are common in PD and result in a more aggressive disease course.

Association Between Glucocerebrosidase Mutations and Parkinson's Disease in Ireland

Multiple studies implicate heterozygous GBA mutations as a major genetic risk factor for Parkinson's disease (PD); however, the frequency of mutations has never been examined in PD patients from the Irish population. We prospectively recruited 314 unrelated Irish PD patients (UK Brain Bank Criteria) and 96 Irish healthy controls (without any signs or family history of parkinsonism) attending. The Dublin Neurological Institute (DNI). Complete exon GBA Sanger sequencing analysis with flanking intronic regions was performed. The GBA carrier frequency was 8.3% in PD and 3.1% in controls. We identified a number of potentially pathogenic mutations including a p.G195E substitution and a p.G377C variant, previously described in a case study of Gaucher's disease in Ireland. On genotype–phenotype assessment hallucinations, dyskinesia, and dystonia were more prevalent in GBA-PD. The genetic etiology of PD in Ireland differs from the continental Europe as seen with the lower LRRK2 and higher than in most European countries GBA mutation frequency. Determining genetic risk factors in different ethnicities will be critical for future personalized therapeutic approach.

GBA mutations p.N370S and p.L444P are associated with Parkinson's disease in patients from Northern Brazil

Mutations of the GBA gene have been reported in patients with Parkinson's disease (PD) from a number of different countries, including Brazil. In order to confirm this pattern in a sample of PD patients from northern Brazil, we conducted a case-control study of the occurrence of the two most common mutations of the GBA gene (c.1226A>G; p.N370S and c.1448T>C; p.L444P) in a group of 81 PD patients and 81 control individuals, using PCR-RFLP, confirmed by the direct sequencing of the PCR products. In the patient group, three patients (3.7%) were heterozygous for the GBA c.1226A>G; p.N370S mutation, and three (3.7%) for GBA c.1448T>C; p.L444P Neither mutation was detected in the control group (p =0.0284). Patients with the c.1448T>C; p.L444P mutation showed a tendency to have an earlier disease onset, but a larger sample number is required to confirm this observation. Our results suggest an association between the GBA c.1226A>G; p.N370S and c.1448T>C; p.L444P mutations and the development of PD in the population of patients from the Northern Brazil.

The Genetic Architecture of Parkinson Disease in Spain: Characterizing Population-Specific Risk, Differential Haplotype Structures, and Providing Etiologic Insight

BACKGROUND

The Iberian Peninsula stands out as having variable levels of population admixture and isolation, making Spain an interesting setting for studying the genetic architecture of neurodegenerative diseases.

OBJECTIVES

To perform the largest PD genome-wide association study restricted to a single country.

METHODS

We performed a GWAS for both risk of PD and age at onset in 7,849 Spanish individuals. Further analyses included population-specific risk haplotype assessments, polygenic risk scoring through machine learning, Mendelian randomization of expression, and methylation data to gain insight into disease-associated loci, heritability estimates, genetic correlations, and burden analyses.

RESULTS

We identified a novel population-specific genome-wide association study signal at PARK2 associated with age at onset, which was likely dependent on the c.155delA mutation. We replicated four genome-wide independent signals associated with PD risk, including SNCA, LRRK2, KANSL1/MAPT, and HLA-DQB1. A significant trend for smaller risk haplotypes at known loci was found compared to similar studies of non-Spanish origin. Seventeen PD-related genes showed functional consequence by two-sample Mendelian randomization in expression and methylation data sets. Long runs of homozygosity at 28 known genes/loci were found to be enriched in cases versus controls.

CONCLUSIONS

Our data demonstrate the utility of the Spanish risk haplotype substructure for future fine-mapping efforts, showing how leveraging unique and diverse population histories can benefit genetic studies of complex diseases. The present study points to PARK2 as a major hallmark of PD etiology in Spain. © 2019 International Parkinson and Movement Disorder Society.

GBA-Associated Parkinson's Disease and Other Synucleinopathies

PURPOSE OF REVIEW

GBA mutations are the most common known genetic cause of Parkinson's disease (PD). Its biological pathway may be important in idiopathic PD, since activity of the enzyme encoded by GBA, glucocerebrosidase, is reduced even among PD patients without GBA mutations. This article describes the structure and function of GBA, reviews recent literature on the clinical phenotype of GBA PD, and suggests future directions for research, counseling, and treatment.

RECENT FINDINGS

Several longitudinal studies have shown that GBA PD has faster motor and cognitive progression than idiopathic PD and that this effect is dose dependent. New evidence suggests that GBA mutations may be important in multiple system atrophy. Further, new interventional studies focusing on GBA PD are described. These studies may increase the interest of PD patients and caregivers in genetic counseling. GBA mutation status may help clinicians estimate PD progression, though mechanisms underlying GBA and synucleinopathy require further understanding.

The Association between E326K of GBA and the Risk of Parkinson's Disease

It is reported that both the homozygous and heterozygous states of GBA mutations which are the causes of Gaucher disease (GD) are linked to the risk of PD. However, the GBA variant p.E326K (c.1093G > A, rs2230288), which does not result in GD in homozygous carriers, has triggered debate among experts studying Parkinson's disease (PD). In order to determine if the E326K variant of GBA is associated with the risk of PD, a standard meta-analysis was conducted by searching and screening publications, data extraction, and statistical analysis. Finally, a total of 15 publications, containing 5,908 PD patients and 5,605 controls, were included in this analysis. The pooled OR of the E326K genotype analysis was 1.99 (95% CI: 1.57–2.51). The minor allele frequencies of E326K for PD patients and controls were 1.67% and 1.03%, respectively. The pooled OR for the minor allele A was 1.99 (95% CI: 1.58–2.50). According to the subgroup analysis, we found that the significant differences between PD patients and controls for both genotype and allele of E326K also exist in Asians and Caucasians, respectively. In this study, we found that E326K of GBA is associated with the risk of PD in total populations, Asians, and Caucasians, respectively. Further studies are needed to clarify the role of GBA in the pathogenesis of PD.

Integrated Genetic Analysis of Racial Differences of Common GBA Variants in Parkinson's Disease: A Meta-Analysis

Background: Numerous studies have indicated that there is a possible relationship between GBA variants and Parkinson's disease (PD), however, most of them focused on a few variants such as L444P, N370S. We performed a comprehensive pooled analysis to clarify the relationship between variations of GBA and the risk of PD in different racial groups.

Methods: Standard meta-analysis was conducted, including generating inclusion and exclusion criteria, searching literature, extracting and analyzing data.

Results: Fifty studies containing 20,267 PD patients and 24,807 controls were included. We found that variants 84insGG, IVS2+1G>A, R120W, H255Q, E326K, T369M, N370S, D409H, L444P, R496H and RecNciI increased the risk of PD in total populations (OR: 1.78–10.49; p: <0.00001, 0.00005, 0.0008, 0.005, <0.00001, 0.004, <0.00001, 0.0003, <0.00001, <0.0001, 0.0001). In subgroup analysis by ethnicity, in AJ populations, variants 84insGG, R496H, N370S increased the risk of PD (OR: 9.26–3.51; p: <0.00001, <0.0001, <0.00001). In total non-AJ populations, variants L444P, R120W, IVS2+1G>A, H255Q, N370S, D409H, RecNciI, E326K, T369M increased the risk of PD (OR: 8.66–1.89; p: <0.00001, 0.0008, 0.02, 0.005, <0.00001, 0.001, 0.0001, <0.00001, 0.002). Among the non-AJ populations, pooled analysis from five different groups were done separately. Variants L444P, N370S, H255Q, D409H, RecNciI, E326K increased risk of PD (OR: 6.52–1.84; p: <0.00001, <0.00001, 0.005, 0.005, 0.04, <0.00001) in European/West Asians while R120W and RecNciI in East Asians (OR: 14.93, 3.56; p: 0.001, 0.003). L444P increased the risk of PD in Hispanics, East Asians and Mixed populations (OR: 15.44, 12.43, 7.33; p: 0.00004, <0.00001, 0.009). Lacking of enough original studies, we failed to conduct quantitative analysis in Africa.

Conclusions: Obvious racial differences were found for GBA variants in PD. 84insGG and R496H exclusively increased PD risks in AJ populations, so did L444P, R120W, IVS2+1G>A, H255Q, D409H, RecNciI, E326K, T369M in non-AJ populations. N370S increased the risk of PD in both ethnics. In non-AJ subgroup populations, N370S, H255Q, D409H, E326K exclusively increased PD risks in European/West Asians, as were R120W in East Asians. L444P increased the risk of PD in all groups in non-AJ ethnicity. These results will contribute to the future genetic screening of GBA gene in PD.

Association of GBA Mutations and the E326K Polymorphism With Motor and Cognitive Progression in Parkinson Disease

Importance

Parkinson disease (PD) is heterogeneous in symptom manifestation and rate of progression. Identifying factors that influence disease progression could provide mechanistic insight, improve prognostic accuracy, and elucidate novel therapeutic targets.

Objective

To determine whether GBA mutations and the E326K polymorphism modify PD symptom progression.

Design, Setting, and Participants

The entire GBA coding region was screened for mutations and E326K in 740 patients with PD enrolled at 7 sites from the PD Cognitive Genetics Consortium. Detailed longitudinal motor and cognitive assessments were performed with patients in the on state.

Main Outcomes and Measures

Linear regression was used to test for an association between GBA genotype and motor progression, with the Movement Disorder Society-sponsored version of the Unified Parkinson's Disease Rating Scale Part III (MDS-UPDRS III) score at the last assessment as the outcome and GBA genotype as the independent variable, with adjustment for levodopa equivalent dose, sex, age, disease duration, MDS-UPDRS III score at the first assessment, duration of follow-up, and site. Similar methods were used to examine the association between genotype and tremor and postural instability and gait difficulty (PIGD) scores. To examine the effect of GBA genotype on cognitive progression, patients were classified into those with conversion to mild cognitive impairment or dementia during the study (progression) and those without progression. The association between GBA genotype and progression status was then tested using logistic regression, adjusting for sex, age, disease duration, duration of follow-up, years of education, and site.

Results

Of the total sample of 733 patients who underwent successful genotyping, 226 (30.8%) were women and 507 (69.2%) were men (mean [SD] age, 68.1 [8.8] years). The mean (SD) duration of follow-up was 3.0 (1.7) years. GBA mutations (β = 4.65; 95% CI, 1.72-7.58; P = .002), E326K (β = 3.42; 95% CI, 0.66-6.17; P = .02), and GBA variants combined as a single group (β = 4.01; 95% CI, 1.95-6.07; P = 1.5 × 10-4) were associated with a more rapid decline in MDS-UPDRS III score. Combined GBA variants (β = 0.38; 95% CI, 0.23-0.53; P = .01) and E326K (β = 0.64; 95% CI, 0.43-0.86; P = .002) were associated with faster progression in PIGD scores, but not in tremor scores. A significantly higher proportion of E326K carriers (10 of 21 [47.6%]; P = .01) and GBA variant carriers (15 of 39 [38.5%]; P = .04) progressed to mild cognitive impairment or dementia.

Conclusions and Relevance

GBA variants predict a more rapid progression of cognitive dysfunction and motor symptoms in patients with PD, with a greater effect on PIGD than tremor. Thus, GBA variants influence the heterogeneity in symptom progression observed in PD.

GBA Variants Influence Motor and Non-Motor Features of Parkinson's Disease

The presence of mutations in glucocerebrosidase (GBA) gene is a known factor increasing the risk of developing Parkinson’s disease (PD). Mutations carriers have earlier disease onset and are more likely to develop neuropsychiatric symptoms than other sporadic PD cases. These symptoms have primarily been observed in Parkinson’s patients carrying the most common pathogenic mutations L444P and N370S. However, recent findings suggest that other variants across the gene may have a different impact on the phenotype as well as on the disease progression. We aimed to explore the influence of variants across GBA gene on the clinical features and treatment related complications in PD. In this study, we screened the GBA gene in a cohort of 532 well-characterised PD patients and 542 controls from southern Spain. The potential pathogeniticy of the identified variants was assessed using in-silico analysis and subsequently classified as benign or deleterious. As a result, we observed a higher frequency of GBA variants in PD patients (12.2% vs. 7.9% in controls, p = 0.021), earlier mean age at disease onset in GBA variant carriers (50.6 vs. 56.6 years; p = 0.013), as well as more prevalent motor and non-motor symptoms in patients carrying deleterious variants. In addition, we found that dopaminergic motor complications are influenced by both benign and deleterious variants. Our results highlight the fact that the impact on the phenotype highly depends on the potential pathogenicity of the carried variants. Therefore, the course of motor and non-motor symptoms as well as treatment-related motor complications could be influenced by GBA variants.

The genetic background of Parkinson's disease: current progress and future prospects

Almost two decades of genetic research in Parkinson's disease (PD) have remarkably increased our knowledge regarding the genetic basis of PD with numerous genes and genetic loci having been found to cause familial PD or affect the risk for PD. Approximately 5-10% of PD patients have monogenic forms of the disease, exhibiting a classical Mendelian type of inheritance, however, the majority PD cases are sporadic, probably caused by a combination of genetic and environmental risk factors. Nowadays, six genes, alpha synuclein, LRRK2, VPS35, Parkin, PINK1 and DJ-1, have definitely been associated with an autosomal dominant or recessive PD mode of inheritance. The advent of genome-wide association studies (GWAS) and the implementation of new technologies, like next generation sequencing (NGS) and exome sequencing has undoubtedly greatly aided the identification on novel risk variants for sporadic PD. In this review, we will summarize the current progress and future prospects in the field of PD genetics.

Oligomeric α-synuclein and glucocerebrosidase activity levels in GBA-associated Parkinson's disease

Alpha-synuclein oligomerization plays a key role in the development of Parkinson's disease (PD). Being the most common genetic contributor to PD, glucocerebrosidase 1 (GBA) mutations have been associated with decreased GBA enzymatic activity in PD patients with mutations in the GBA gene (GBA-PD). However, it is unknown whether the activities of other lysosomal hydrolases are being altered in GBA-PD patients and are accompanied by an increase in alpha-synuclein oligomerization. The aim of our study was to estimate GBA enzymatic activity as well as the activities of five other lysosomal hydrolases (galactocerebrosidase, alpha-glucosidase, alpha-galactosidase, sphingomyelinase, alpha-iduronidase) in dried blood spots with assessing plasma oligomeric alpha-synuclein levels in sporadic PD (sPD) patients, in GBA-PD patients and in controls. GBA enzymatic activity and plasma oligomeric alpha-synuclein levels were assessed in sPD patients (N=84), in GBA-PD patients (N=21) and controls (N=62) by LC-MS/MS and ELISA methods accordingly. GBA-PD patients showed lower GBA enzymatic activity compared to controls (p=0.001) and to sPD (p=0.0001). We also found the reduction of GLA enzymatic activity (but not of other lysosomal hydrolases) in GBA-PD (p=0.001). At the same time plasma oligomeric alpha-synuclein levels were increased in GBA-PD group compared to sPD and controls (p=0.002 and p<0.0001, respectively). Our results suggest that the decrease in enzymatic activity of lysosomal hydrolases in GBA mutation carriers may contribute to PD pathogenesis by increasing the level of neurotoxic oligomeric alpha-synuclein species.

Mutations in glucocerebrosidase are a major genetic risk factor for Parkinson's disease and increase susceptibility to dementia in a Flanders-Belgian cohort

OBJECTIVE

To investigate the frequency of glucocerebrosidase (GBA) mutations in a Flanders-Belgian Parkinson's disease (PD) patient cohort and to assess genotype-phenotype correlations.

METHODS

We performed an in-depth sequencing of all coding exons of GBA in 266 clinically well-characterized PD patients and 536 healthy control individuals.

RESULTS

We identified rare, heterozygous GBA mutations in 12 PD patients (4.5%) and in 2 healthy control individuals (0.37%), confirming the genetic association of GBA mutations with PD in the Flanders-Belgian population (p<0.001). The patient carriers had a more severe Unified Parkinson's Disease Rating Scale (UPDRS) motor score than non-carriers. Also, GBA mutation status was a significant, independent predictor for the presence of dementia (OR=12.43, 95% CI: 2.27-68.14. p=0.004). Genetic association of PD with the common p.E326K and p.T369M variants in GBA was absent.

CONCLUSION

In our Flanders-Belgian cohort, carrier status of a heterozygous GBA mutation was a strong genetic risk factor for PD. The GBA mutation frequency of 4.5% is comparable to previously reported data in other European PD patient cohorts. Furthermore, our clinical data suggest a more severe motor phenotype and a strong predisposition to dementia in GBA mutation carriers.

Glucocerebrosidase and parkinsonism: lessons to learn

Both homo- (causing autosomal-recessive Gaucher's disease; GD) and heterozygous mutations in the glucocerebrosidase gene (GBA) are associated with Parkinson's disease (PD), and represent the most robust known genetic susceptibility factors identified in PD. Since the accumulation of α-synuclein has been considered critical to the pathogenesis of PD among several possible pathways through which glucocerebrosidase (GCase) deficiency may promote the pathogenesis of PD, particular attention was given to the reciprocity with α-synuclein levels, lysosomal dysfunction, endoplasmatic reticulum-Golgi trafficking of GCase, dysregulation of calcium homeostasis and mitochondrial abnormalities. The proportion of PD patients that carry GBA mutations is estimated to be approximately between 5 and 10 %. Individual PD patients with or without GBA mutations cannot be discriminated on clinical or pathological grounds. However, GBA mutation carriers may have slightly earlier age at PD onset, more likely have a positive family history for PD, and more prevalent non-motor symptoms when compared to those patients who are not carriers. Establishing the concept of GBA-related PD promoted a search for the pathogenic mechanisms through which GCase deficiency may influence pathogenesis of PD, suggesting that targeting the GCase-lysosomal pathway might be a rational approach for the development of neuroprotective drugs in PD.

The relationship between glucocerebrosidase mutations and Parkinson disease

Parkinson disease (PD) is the second most common neurodegenerative disorder after Alzheimer disease, whereas Gaucher disease (GD) is the most frequent lysosomal storage disorder caused by homozygous mutations in the glucocerebrosidase (GBA1) gene. Increased risk of developing PD has been observed in both GD patients and carriers. It has been estimated that GBA1 mutations confer a 20‐ to 30‐fold increased risk for the development of PD, and that at least 7–10% of PD patients have a GBA1 mutation. To date, mutations in the GBA1 gene constitute numerically the most important risk factor for PD. The type of PD associated with GBA1 mutations (PD‐GBA1) is almost identical to idiopathic PD, except for a slightly younger age of onset and a tendency to more cognitive impairment. Importantly, the pathology of PD‐GBA1 is identical to idiopathic PD, with nigral dopamine cell loss, Lewy bodies, and neurites containing alpha‐synuclein. The mechanism by which GBA1 mutations increase the risk for PD is still unknown. However, given that clinical manifestation and pathological findings in PD‐GBA1 patients are almost identical to those in idiopathic PD individuals, it is likely that, as in idiopathic PD, alpha‐synuclein accumulation, mitochondrial dysfunction, autophagic impairment, oxidative and endoplasmic reticulum stress may contribute to the development and progression of PD‐GBA1. Here, we review the GBA1 gene, its role in GD, and its link with PD.

The impact of glucocerebrosidase 1 (GBA1) mutations on functioning of endoplasmic reticulum (ER), lysosomes, and mitochondria. GBA1 mutations resulting in production of misfolded glucocerebrosidase (GCase) significantly affect the ER functioning. Misfolded GCase trapped in the ER leads to both an increase in the ubiquitin–proteasome system (UPS) and the ER stress. The presence of ER stress triggers the unfolded protein response (UPR) and/or endoplasmic reticulum‐associated degradation (ERAD). The prolonged activation of UPR and ERAD subsequently leads to increased apoptosis. The presence of misfolded GCase in the lysosomes together with a reduction in wild‐type GCase levels lead to a retardation of alpha‐synuclein degradation via chaperone‐mediated autophagy (CMA), which subsequently results in alpha‐synuclein accumulation and aggregation. Impaired lysosomal functioning also causes a decrease in the clearance of autophagosomes, and so their accumulation. GBA1 mutations perturb normal mitochondria functioning by increasing generation of free radical species (ROS) and decreasing adenosine triphosphate (ATP) production, oxygen consumption, and membrane potential. GBA1 mutations also lead to accumulation of dysfunctional and fragmented mitochondria.

This article is part of a special issue on Parkinson disease.

Mutations of glucocerebrosidase gene and susceptibility to Parkinson's disease: An updated meta-analysis in a European population

This meta-analysis aims to investigate the association between mutations of glucocerebrosidase (GBA) gene and susceptibility to Parkinson's disease (PD) in a European population. Several electronic databases were extensively searched. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to assess the association. In total, fourteen published papers screening L444P, N370S and other GBA variants were identified. The GBA mutations were significantly associated with PD in the European population. Subgroup analysis stratified by the age of onset (AAO) revealed that the association between GBA mutations and PD existed in the patients with age at onset ⩽50 years but did not exist in the patients with age at onset >50 years. Furthermore, the associations between N370S, and L444P with PD were also analyzed to explore the roles of the two most frequent GBA mutations in the development of PD. The results showed that significant associations between N370S, and L444P with PD were observed, respectively. Overall, the study supported that GBA mutations were a risk factor for PD in the European population. Patients with early-onset were more likely to carry GBA mutations than those with late-onset. Moreover, both L444P and N370S were associated with increased PD risk.

From rare to common and back again: 60years of lysosomal dysfunction

Sixty years after its discovery, the lysosome is no longer considered as cell's waste bin but as an organelle playing a central role in cell metabolism. Besides its well known association with lysosomal storage disorders (mostly rare and life-threatening diseases), recent data have shown that the lysosome is also a player in some of the most common conditions of our time; and, perhaps even most important, it is not only a target for orphan drugs (rare disease therapeutic approaches) but also a putative target to treat patients suffering from common complex diseases worldwide. Here we review the striking associations linking rare lysosomal storage disorders such as the well-known Gaucher disease, or even the recently discovered, extremely rare Neuronal Ceroid Lipofuscinosis-11 and some of the most frequent, multifaceted and complex disorders of modern society such as cancer, Parkinson's disease and frontotemporal lobar degeneration.

An assessment of the frequency of mutations in the GBA and VPS35 genes in Hungarian patients with sporadic Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder, with cases of either familial or sporadic origin. Several polymorphisms in a number of genes have been proved to have an important role in the development of PD. Particular attention has recently been paid to genes of the glucocerebrosidase (GBA) and the vacuolar protein sorting-associated protein 35 (VPS35). In this study, the three most common mutations (L444P, N370S and R120W) of the GBA gene and the D620N mutation of the VPS35 gene were examined in 124 Hungarian patients diagnosed with sporadic PD (SPD) and 122 control subjects. The frequency of the L444P mutation of the GBA gene proved to be higher in the PD patients (2.4%) than in the controls (0%), although the difference was not statistically significant. All the patients who carried the mutant allele were in the early-onset PD (EOPD) group. However, neither the R120W nor the N370S variant of the GBA gene nor D620N mutation of the VPS35 gene were detected among the PD cases or the controls. Even though these results suggest that the studied mutations are quite rare in SPD patients, the most frequent L444P mutation of the GBA gene may be associated with the development of EOPD in the Hungarian population.

Analysis of the genetic variability in Parkinson's disease from Southern Spain

To date, a large spectrum of genetic variants has been related to familial and sporadic Parkinson's disease (PD) in diverse populations worldwide. However, very little is known about the genetic landscape of PD in Southern Spain, despite its particular genetic landscape coming from multiple historical migrations. We included 134 PD patients in this study, of which 97 individuals were diagnosed with late-onset sporadic PD (LOPD), 28 with early-onset sporadic PD (EOPD), and 9 with familial PD (FPD). Genetic analysis was performed through a next-generation sequencing panel to screen 8 PD-related genes (LRRK2, SNCA, PARKIN, PINK1, DJ-1, VPS35, GBA, and GCH1) in EOPD and FPD groups and direct Sanger sequencing of GBA exons 8-11 and LRRK2 exons 31 and 41 in the LOPD group. In the EOPD and FPD groups, we identified 11 known pathogenic mutations among 15 patients (40.5%). GBA (E326K, N370S, D409H, L444P) mutations were identified in 7 patients (18.9%); LRRK2 (p.R1441G and p.G2019S) in 3 patients (8.1%); biallelic PARK2 mutations (p.N52fs, p.V56E, p.C212Y) in 4 cases (10.8%) and PINK1 homozygous p.G309D in 1 patient (2.7%). An EOPD patient carried a single PARK2 heterozygous mutation (p.R402C), and another had a novel heterozygous mutation in VPS35 (p.R32S), both of unknown significance. Moreover, pathogenic mutations in GBA (E326K, T369M, N370S, D409H, L444P) and LRRK2 (p.R1441G and p.G2019S) were identified in 13 patients (13.4%) and 4 patients (4.1%), respectively, in the LOPD group. A large number of known pathogenic mutations related to PD have been identified. In particular, GBA and LRRK2 mutations appear to be considerably frequent in our population, suggesting a strong Jewish influence. Further research is needed to study the contribution of the novel found mutation p.R32S in VPS35 to the pathogenesis of PD.

Glucocerebrosidase gene therapy prevents α-synucleinopathy of midbrain dopamine neurons

Diminished lysosomal function can lead to abnormal cellular accumulation of specific proteins, including α-synuclein, contributing to disease pathogenesis of vulnerable neurons in Parkinson's disease (PD) and related α-synucleinopathies. GBA1 encodes for the lysosomal hydrolase glucocerebrosidase (GCase), and mutations in GBA1 are a prominent genetic risk factor for PD. Previous studies showed that in sporadic PD, and in normal aging, GCase brain activity is reduced and levels of corresponding glycolipid substrates are increased. The present study tested whether increasing GCase through AAV-GBA1 intra-cerebral gene delivery in two PD rodent models would reduce the accumulation of α-synuclein and protect midbrain dopamine neurons from α-synuclein-mediated neuronal damage. In the first model, transgenic mice overexpressing wildtype α-synuclein throughout the brain (ASO mice) were used, and in the second model, a rat model of selective dopamine neuron degeneration was induced by AAV-A53T mutant α-synuclein. In ASO mice, intra-cerebral AAV-GBA1 injections into several brain regions increased GCase activity and reduced the accumulation of α-synuclein in the substantia nigra and striatum. In rats, co-injection of AAV-GBA1 with AAV-A53T α-synuclein into the substantia nigra prevented α-synuclein-mediated degeneration of nigrostriatal dopamine neurons by 6 months. These neuroprotective effects were associated with altered protein expression of markers of autophagy. These experiments demonstrate, for the first time, the neuroprotective effects of increasing GCase against dopaminergic neuron degeneration, and support the development of therapeutics targeting GCase or other lysosomal genes to improve neuronal handling of α-synuclein.

Mutations in the glucocerebrosidase gene are common in patients with Parkinson's disease from Eastern Canada

BACKGROUND

Mutations in the β-glucocerebrosidase gene (GBA) have been implicated as a risk factor for Parkinson's disease (PD). However, GBA mutations in PD patients of different ethnic origins were reported to be inconsistent.

METHODS

We sequenced all exons of the GBA gene in 225 PD patients and 110 control individuals from Eastern Canada.

RESULT

Two novel GBA variants of c.-119 A/G and S(-35)N, five known GBA mutations of R120W, N370S, L444P, RecNciI and RecTL mutation (del55/D409H/RecNciI) as well as two non-pathological variants of E326K and T369M were identified from PD patients while only one mutation of S13L and two non-pathological variants of E326K and T369M were found in the control individuals. The frequency of GBA mutations within PD patients (4.4%) is 4.8 times higher than the 0.91% observed in control individuals (X(2) = 2.91, p = 0.088; odds ratio = 4.835; 95% confidence interval = 2.524-9.123). The most common mutations of N370S and L444P accounted for 36.0% (9/25) of all the GBA mutations in this Eastern Canadian PD cohort. The frequency (6.67%) of E326K and T369M in PD patients is comparable to 7.27% in control individuals (X(2) = 0.042, p = 0.8376), further supporting that these two variants have no pathological effects on PD. Phenotype analysis showed that no significant difference in family history, age at onset and cognitive impairment was identified between the GBA mutation carriers and non-GBA mutation carriers.

CONCLUSION

GBA mutations were found to be a common genetic risk factor for PD in Eastern Canadian patients.

Glucocerebrosidase activity in Parkinson's disease with and without GBA mutations

Glucocerebrosidase (GBA) mutations have been associated with Parkinson's disease in numerous studies. However, it is unknown whether the increased risk of Parkinson's disease in GBA carriers is due to a loss of glucocerebrosidase enzymatic activity. We measured glucocerebrosidase enzymatic activity in dried blood spots in patients with Parkinson's disease (n = 517) and controls (n = 252) with and without GBA mutations. Participants were recruited from Columbia University, New York, and fully sequenced for GBA mutations and genotyped for the LRRK2 G2019S mutation, the most common autosomal dominant mutation in the Ashkenazi Jewish population. Glucocerebrosidase enzymatic activity in dried blood spots was measured by a mass spectrometry-based assay and compared among participants categorized by GBA mutation status and Parkinson's disease diagnosis. Parkinson's disease patients were more likely than controls to carry the LRRK2 G2019S mutation (n = 39, 7.5% versus n = 2, 0.8%, P < 0.001) and GBA mutations or variants (seven homozygotes and compound heterozygotes and 81 heterozygotes, 17.0% versus 17 heterozygotes, 6.7%, P < 0.001). GBA homozygotes/compound heterozygotes had lower enzymatic activity than GBA heterozygotes (0.85 µmol/l/h versus 7.88 µmol/l/h, P < 0.001), and GBA heterozygotes had lower enzymatic activity than GBA and LRRK2 non-carriers (7.88 µmol/l/h versus 11.93 µmol/l/h, P < 0.001). Glucocerebrosidase activity was reduced in heterozygotes compared to non-carriers when each mutation was compared independently (N370S, P < 0.001; L444P, P < 0.001; 84GG, P = 0.003; R496H, P = 0.018) and also reduced in GBA variants associated with Parkinson's risk but not with Gaucher disease (E326K, P = 0.009; T369M, P < 0.001). When all patients with Parkinson's disease were considered, they had lower mean glucocerebrosidase enzymatic activity than controls (11.14 µmol/l/h versus 11.85 µmol/l/h, P = 0.011). Difference compared to controls persisted in patients with idiopathic Parkinson's disease (after exclusion of all GBA and LRRK2 carriers; 11.53 µmol/l/h, versus 12.11 µmol/l/h, P = 0.036) and after adjustment for age and gender (P = 0.012). Interestingly, LRRK2 G2019S carriers (n = 36), most of whom had Parkinson's disease, had higher enzymatic activity than non-carriers (13.69 µmol/l/h versus 11.93 µmol/l/h, P = 0.002). In patients with idiopathic Parkinson's, higher glucocerebrosidase enzymatic activity was associated with longer disease duration (P = 0.002) in adjusted models, suggesting a milder disease course. We conclude that lower glucocerebrosidase enzymatic activity is strongly associated with GBA mutations, and modestly with idiopathic Parkinson's disease. The association of lower glucocerebrosidase activity in both GBA mutation carriers and Parkinson's patients without GBA mutations suggests that loss of glucocerebrosidase function contributes to the pathogenesis of Parkinson's disease. High glucocerebrosidase enzymatic activity in LRRK2 G2019S carriers may reflect a distinct pathogenic mechanism. Taken together, these data suggest that glucocerebrosidase enzymatic activity could be a modifiable therapeutic target.

Progressive decline of glucocerebrosidase in aging and Parkinson's disease

The principal risk factor for developing most adult onset neurodegenerative diseases is aging, with incidence rising significantly after age 50. Despite research efforts, the causes of Parkinson's disease (PD) remain unknown. As neurons age, they show signs of diminished lysosomal and mitochondrial function, including increased oxidative stress and accumulation of misfolded proteins, and these changes become exacerbated PD. We show that activity of the lysosomal hydrolase glucocerebrosidase gradually diminishes with age in the substantia nigra and putamen of healthy controls. This reduction is comparable to glucocerebrosidase activity in GBA1-mutation carrier PD patients. These data, demonstrate for the first time that an age-dependent reduction in glucocerebrosidase activity may lower the threshold for developing PD.

Differential effects of severe vs mild GBA mutations on Parkinson disease

OBJECTIVE

To better define the genotype-phenotype correlations between the type of GBA (glucosidase, beta, acid) mutation, severe or mild, and the risk and age at onset (AAO), and potential mechanism of Parkinson disease (PD).

METHODS

We analyzed 1,000 patients of Ashkenazi-Jewish descent with PD for 7 founder GBA mutations, and conducted a meta-analysis of risk and AAO according to GBA genotype (severe or mild mutation). The meta-analysis included 11,453 patients with PD and 14,565 controls from worldwide populations. The statistical analysis was done with and without continuity correction (constant or empirical), considering biases that could potentially affect the results.

RESULTS

Among Ashkenazi-Jewish patients with PD, the odds ratios for PD were 2.2 and 10.3 for mild and severe GBA mutation carriers, respectively. The observed frequency of severe GBA mutation carriers among patients with PD was more than 4-fold than expected (4.4% vs 0.9%, respectively, p < 0.0001, Fisher exact test). In the different models of the meta-analysis, the odds ratios for PD ranged between 2.84 and 4.94 for mild GBA mutation carriers and 9.92 and 21.29 for severe GBA mutation carriers (p < 1 × 10(-6) for all analyses). Pooled analysis demonstrated AAO of 53.1 (±11.2) and 58.1 (±10.6) years for severe and mild GBA mutation carriers, respectively (p = 4.3 × 10(-5)).

CONCLUSIONS

These data demonstrate that mild and severe heterozygous GBA mutations differentially affect the risk and the AAO of PD. Our results have important implications for genetic counseling and clinical follow-up.

Glucocerebrosidase gene mutations associated with Parkinson's disease: a meta-analysis in a Chinese population

Mutations of glucocerebrosidase (GBA) confer susceptibility to Parkinson's disease in several ethnical populations, with a high incidence especially in the Ashkenazi Jewish population. Although there are several studies that have investigated a similar association in a Chinese population, small sample sizes and few positive outcomes have made it difficult to obtain conclusive results from these individual studies. Therefore, the present study used a meta-analysis approach, pooling the appropriate data from published studies to investigate the association of GBA mutations and Parkinson's disease in a Chinese population. Nine studies containing 6536 Chinese subjects (3438 cases and 3098 healthy controls) and examining the GBA mutations of L444P, N370S and several other mutations were included. Review Manager 5.2 software was applied to analyze the pooled odds ratios (ORs) and 95% confidence intervals (CIs). The results showed a significant association of Parkinson's disease risk with overall GBA mutations (OR = 6.34, 95% CI = 3.77–10.68, p<0.00001), and with the subgroup of L444P mutation (OR = 11.68, 95% CI = 5.23–26.06, p<0.00001). No such association was observed for the subgroup with N370S mutation or other mutations, in part because of the small sample size or rare events. Thus, for the rare occurrence of GBA mutations, studies with larger sample size are necessary to minimize the sampling error and to obtain convincing results.

Mutations in the glucocerebrosidase gene are responsible for Chinese patients with Parkinson's disease

Pathological mutations in the glucocerebrosidase gene (GBA) have been suggested to be associated with Parkinson's disease (PD) in various ethnic populations. Most studies on Chinese PD patients have only screened the N370S and L444P mutations in the GBA gene. To investigate the GBA mutations in Chinese population, we performed complete sequencing of the GBA gene in 184 Chinese PD patients and 130 Chinese control individuals. As a result, we identified three novel and nine reported GBA mutations. The novel mutations include 5-bp deletion (c.334_338delCAGAA), L264I and L314V and the nine reported GBA mutations are R163Q, F213I, E326K, S364S, F347L, V375L, L444P, RecNciI and Q497R. The novel 5-bp deletion (CAGAA) produces a short truncated GBA protein of 142 amino acids, which loses major function domains of the 536 amino acids. Our data also reveals that the frequency of GBA mutations within this Chinese PD cohort was 8.7%, which is significantly higher than 1.54% observed in the Chinese control cohort (χ(2) = 7.22, P = 0.0072; odds ratio (OR) = 6.095, 95% confidence interval of OR = 1.546-24.030). The most common L444P mutation accounts 2.74%, which confer more genetic risk for PD in this Chinese population. In conclusion, novel and known GBA mutations were identified and were found to be associated to PD in this Chinese population.

Glucocerebrosidase mutations in primary parkinsonism

Introduction

Mutations in the lysosomal glucocerebrosidase (GBA) gene increase the risk of Parkinson's Disease (PD). We determined the frequency and relative risk of major GBA mutations in a large series of Italian patients with primary parkinsonism.

Methods

We studied 2766 unrelated consecutive patients with clinical diagnosis of primary degenerative parkinsonism (including 2350 PD), and 1111 controls. The entire cohort was screened for mutations in GBA exons 9 and 10, covering approximately 70% of mutations, including the two most frequent defects, p.N370S and p.L444P.

Results

Four known mutations were identified in heterozygous state: 3 missense mutations (p.N370S, p.L444P, and p.D443N), and the splicing mutation IVS10+1G>T, which results in the in-frame exon-10 skipping. Molecular characterization of 2 additional rare variants, potentially interfering with splicing, suggested a neutral effect. GBA mutations were more frequent in PD (4.5%, RR = 7.2, CI = 3.3–15.3) and in Dementia with Lewy Bodies (DLB) (13.8%, RR = 21.9, CI = 6.8–70.7) than in controls (0.63%). but not in the other forms of parkinsonism such as Progressive Supranuclear Palsy (PSP, 2%), and Corticobasal Degeneration (CBD, 0%). Considering only the PD group, GBA-carriers were younger at onset (52 ± 10 vs. 57 ± 10 years, P < 0.0001) and were more likely to have a positive family history of PD (34% vs. 20%, P < 0.001).

Conclusion

GBA dysfunction is relevant for synucleinopathies, such as PD and DLB, except for MSA, in which pathology involves oligodendrocytes, and the tauopathies PSP and CBD. The risk of developing DLB is three-fold higher than PD, suggesting a more aggressive phenotype.

•

We screened a large case–control cohort with parkinsonism for common GBA mutations.

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GBA mutations in the Italian population are a risk factor for Lewy Bodies Diseases (PD and DLB).

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GBA mutations were not increased in the other forms of parkinsonism: PSP, CBD and MSA.

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GBA dysfunction does not seem to be involved in MSA and tauopathies.

The association between ß-glucocerebrosidase mutations and parkinsonism

Mutations in the ß-glucocerebrosidase gene (GBA), which encodes the lysosomal enzyme ß-glucocerebrosidase, have traditionally been implicated in Gaucher disease, an autosomal recessive lysosomal storage disorder. Yet the past two decades have yielded an explosion of epidemiological and basic-science evidence linking mutations in GBA with the development of Parkinson disease (PD) as well. Although the specific contribution of mutant GBA to the pathogenesis of parkinsonism remains unknown, evidence suggests that both loss of function and toxic gain of function by abnormal ß-glucocerebrosidase may be important, and implicates a close relationship between ß-glucocerebrosidase and α-synuclein. Furthermore, multiple lines of evidence suggest that although GBA-associated PD closely mimics idiopathic PD (IPD), it may present at a younger age, and is more frequently complicated by cognitive dysfunction. Understanding the clinical association between GBA and PD, and the relationship between ß-glucocerebrosidase and α-synuclein, may enhance understanding of the pathogenesis of IPD, improve prognostication and treatment of GBA carriers with parkinsonism, and furthermore inform therapies for IPD not due to GBA mutations.

Genetic convergence of Parkinson's disease and lysosomal storage disorders

Parkinson's disease is a common progressive neurodegenerative disorder characterized by predominant degeneration of the dopaminergic neurons in the substantia nigra pars compacta and the presence of intracellular inclusions enriched in α-synuclein, resulting in a variety motor and nonmotor symptoms. Lysosomal storage disorders are a group of disorders including Gaucher disease, Niemann-Pick disease, and neuronal ceroid lipofuscinoses caused by the defective activity of lysosomal and nonlysosomal proteins. In addition to an overlap in some clinical features between lysosomal storage disorders and Parkinson's disease, the two disorders may be also linked pathogenically. There is growing support for the notion that mutations in genes causing lysosomal storage disorders including the glucocerebrosidase gene, the sphingomyelin phosphodiesterase 1 gene, and the NPC1 gene may increase risk for developing Parkinson's disease. In this review, we discuss the recent advances in the genetic convergence of Parkinson's disease and lysosomal storage disorders, shedding new light on the understanding of shared pathogenic pathways.

Lysosomal storage disorders and iron

Lysosomal storage disorders are a group of about 50 rare metabolic diseases that result from defects in lysosomal function. The majority is recessively inherited and caused by mutations in genes encoding lysosomal proteins as the basis for its pathobiology. The lysosome plays a pivotal role in a cell's ability to recycle and degrade unwanted material. One of its functions relates to regulating iron levels throughout the body. Iron is a double-edged sword: It is absolutely required for an organism's survival, but high levels of iron quickly lead to cell death. In addition, recent results have put the lysosome on the map of pathways leading to common neurodegenerative diseases, such as Parkinson's disease and Alzheimer's disease. It is plausible that the mechanisms through which the lysosome acts in these diseases also involve iron and this would have significant implications in our understanding of the molecular etiology of these disorders.

Parkinson's disease: from genetics to clinical practice

Breakthroughs in genetics over the last decade have radically advanced our understanding of the etiological basis of Parkinson's disease (PD). Although much research remains to be done, the main genetic causes of this neurodegenerative disorder are now partially unraveled, allowing us to feel more confident that our knowledge about the genetic architecture of PD will continue to increase exponentially. How and when these discoveries will be introduced into general clinical practice, however, remains uncertain. In this review, we provide a general summary of the progress in the genetics of PD and discuss how this knowledge will contribute to the diagnosis and clinical management of patients with, or at risk of this disorder.

A multicenter study of glucocerebrosidase mutations in dementia with Lewy bodies

IMPORTANCE

While mutations in glucocerebrosidase (GBA1) are associated with an increased risk for Parkinson disease (PD), it is important to establish whether such mutations are also a common risk factor for other Lewy body disorders.

OBJECTIVE

To establish whether GBA1 mutations are a risk factor for dementia with Lewy bodies (DLB). DESIGN We compared genotype data on patients and controls from 11 centers. Data concerning demographics, age at onset, disease duration, and clinical and pathological features were collected when available. We conducted pooled analyses using logistic regression to investigate GBA1 mutation carrier status as predicting DLB or PD with dementia status, using common control subjects as a reference group. Random-effects meta-analyses were conducted to account for additional heterogeneity.

SETTING

Eleven centers from sites around the world performing genotyping.

PARTICIPANTS

Seven hundred twenty-one cases met diagnostic criteria for DLB and 151 had PD with dementia. We compared these cases with 1962 controls from the same centers matched for age, sex, and ethnicity.

MAIN OUTCOME MEASURES

Frequency of GBA1 mutations in cases and controls. RESULTS We found a significant association between GBA1 mutation carrier status and DLB, with an odds ratio of 8.28 (95% CI, 4.78-14.88). The odds ratio for PD with dementia was 6.48 (95% CI, 2.53-15.37). The mean age at diagnosis of DLB was earlier in GBA1 mutation carriers than in noncarriers (63.5 vs 68.9 years; P < .001), with higher disease severity scores.

CONCLUSIONS AND RELEVANCE

Mutations in GBA1 are a significant risk factor for DLB. GBA1 mutations likely play an even larger role in the genetic etiology of DLB than in PD, providing insight into the role of glucocerebrosidase in Lewy body disease.

Comprehensive LRRK2 and GBA screening in Portuguese patients with Parkinson's disease: identification of a new family with the LRRK2 p.Arg1441His mutation and novel missense variants

Mutations in the LRRK2 and GBA genes are increasingly recognized as frequent determinants of familial and sporadic Parkinson's disease (PD). However, for several populations, accurate data on the prevalence and types of mutations are not available, because previous studies have not investigated the complete coding regions of these genes in large samples. We studied 312 PD patients ascertained at a single centre in Lisbon, Portugal. In 61 patients, with familial PD, we sequenced the entire open reading frames and exon-intron boundaries of LRRK2 and GBA. In LRRK2, we identified ten heterozygous p.Gly2019Ser (16.4%), and two heterozygous p.Arg1441His carriers (3.3%); furthermore, six patients each carried a novel LRRK2 heterozygous variant (five coding and one 3'-UTR variants) of undetermined pathogenic role. Segregation of the p.Arg1441His mutation with PD was observed in the families of both carriers. None of these variants were identified in 138 healthy controls. Screening of GBA revealed no mutations. In the remaining 251 PD patients (25 familial and 226 sporadic) we found ten additional carriers of the heterozygous p.Gly2019Ser and no carriers of the other mutations. Thus, the p.Gly2019Ser mutation was detected in a total number of 20 carriers out of 312 patients (6.4%), including twelve familial (14%) and eight sporadic patients (3.5%). This comprehensive study confirms that p.Gly2019Ser is the most important genetic cause of PD known so far in Portugal and supports the contention that p.Arg1441His is also a PD-causing mutation. These findings have relevance for the genetic testing and counseling of PD patients in this population.

Greater risk of parkinsonism associated with non-N370S GBA1 mutations

Mutations in β-glucosidase (GBA1) are the most common genetic risk factor for Parkinson disease (PD). There is evidence to suggest that PD risk is greater (1) in GBA1 heterozygotes with non-N370S GBA1 mutations compared to N370S mutations and (2) in GD type 1 (GD1) patients compared to GBA1 heterozygotes. This study aimed to determine the comparative risk of parkinsonism in individuals who are affected or carriers of Gaucher disease (GD) and to ascertain the influence of different GBA1 mutations on risk/clinical expression. We conducted a secondary analysis of cross-sectional data assessing the prevalence of parkinsonism in a population of GD1 patients and their heterozygote and non-carrier family members. Two logistic regression models, both employing a family-specific random effect, were used to assess (1) the association between GBA1 mutation (N370S or non-N370S) and parkinsonism among GBA1 heterozygotes and (2) the association between GBA1 genotype and parkinsonism. Parkinsonism was present in 8.6 % of GD1 (7/81), 8.7 % of GBA1 heterozygotes (18/207), and 2.2 % of non-carriers (1/45). For those greater than 60 years old, parkinsonism was present in 38.5 % (5/13) of GD1 (5/13), 15.3 % of GBA1 heterozygotes (13/85), and 7.1 % of non-carriers (1/14). Among GBA1 heterozygotes, non-N370S mutations were associated with a significantly increased risk of parkinsonism compared to N370S (OR = 22.5; p = 0.035; 95%CI: 1.24, 411). In this population, each additional GBA1 mutation was associated with a non-significant two-fold increased risk of parkinsonism. GBA1 heterozygotes with non-N370S mutations associated with Gaucher disease have an increased risk of parkinsonism compared to those with N370S mutations.

Loss of β-glucocerebrosidase activity does not affect alpha-synuclein levels or lysosomal function in neuronal cells

To date, a plethora of studies have provided evidence favoring an association between Gaucher disease (GD) and Parkinson’s disease (PD). GD, the most common lysosomal storage disorder, results from the diminished activity of the lysosomal enzyme β-glucocerebrosidase (GCase), caused by mutations in the β-glucocerebrosidase gene (GBA). Alpha-synuclein (ASYN), a presynaptic protein, has been strongly implicated in PD pathogenesis. ASYN may in part be degraded by the lysosomes and may itself aberrantly impact lysosomal function. Therefore, a putative link between deficient GCase and ASYN, involving lysosomal dysfunction, has been proposed to be responsible for the risk for PD conferred by GBA mutations. In this current work, we aimed to investigate the effects of pharmacological inhibition of GCase on ASYN accumulation/aggregation, as well as on lysosomal function, in differentiated SH-SY5Y cells and in primary neuronal cultures. Following profound inhibition of the enzyme activity, we did not find significant alterations in ASYN levels, or any changes in the clearance or formation of its oligomeric species. We further observed no significant impairment of the lysosomal degradation machinery. These findings suggest that additional interaction pathways together with aberrant GCase and ASYN must govern this complex relation between GD and PD.

The glucocerobrosidase E326K variant predisposes to Parkinson's disease, but does not cause Gaucher's disease

BACKGROUND

Heterozygous loss-of-function mutations in the acid beta-glucocerebrosidase (GBA1) gene, responsible for the recessive lysosomal storage disorder, Gaucher's disease (GD), are the strongest known risk factor for Parkinson's disease (PD). Our aim was to assess the contribution of GBA1 mutations in a series of early-onset PD.

METHODS

One hundred and eighty-five PD patients (with an onset age of ≤50) and 283 age-matched controls were screened for GBA1 mutations by Sanger sequencing.

RESULTS

We show that the frequency of GBA1 mutations is much higher in this patient series than in typical late-onset patient cohorts. Furthermore, our results reveal that the most prevalent PD-associated GBA1 mutation is E326K, a variant that does not, when homozygous, cause GD.

CONCLUSIONS

Our results confirm recent reports that the mutation, E326K, predisposes to PD and suggest that, in addition to reduced GBA1 activity, other molecular mechanisms may contribute to the development of the disease.

α-Synuclein and mitochondrial dysfunction in Parkinson's disease

α-Synuclein (SNCA) is a substantive component of Lewy bodies, the pathological hallmark of Parkinson's disease (PD). The discovery and subsequent derivation of its role in PD has led to a suprising but fruitful convergence of the fields of biochemistry and molecular genetics. In particular, the manipulation of the cell lines of a number of forms of familial PD has implicated SNCA in distinct and diverse biochemical pathways related to its pathogenesis. This current and rapidly evolving concept indicates PD is a disease in which interacting pathways of oxidative stress, mitochondrial dysfunction and impaired regulation of protein turnover interact to cause dopaminergic cell dysfunction and death. SNCA has a central role in these processes and manipulation of its expression, degradation and aggregation appear to be promising neuroprotective therapeutic targets.

Glucocerebrosidase L444P mutation confers genetic risk for Parkinson's disease in central China

BACKGROUND

Mutations of the glucocerebrosidase (GBA) gene have reportedly been associated with Parkinson disease (PD) in various ethnic populations such as Singaporean, Japanese, Formosan, Canadian, American, Portuguese, Greek, Brazilian, British, Italian, Ashkenazi Jewish, southern and southwestern Chinese. The purpose of this study is to determine in central China whether or not the reported GBA mutations remain associated with PD.

METHODS

In this project, we conducted a controlled study in a cohort of 208 central Chinese PD patients and 298 controls for three known GBA mutations (L444P, N370S and R120W).

RESULTS

Our data reveals a significantly higher frequency of L444P mutation in GBA gene of PD cases (3.4%) compared with the controls (0.3%) (P = 0.007, OR = 10.34, 95% CI = 1.26 - 84.71). Specifically, the frequency of L444P mutation was higher in the late onset PD (LOPD) cases compared with that in control subjects. The N370S and R120W mutations were detected in neither the PD group nor the control subjects.

CONCLUSIONS

Our observations demonstrated that the GBA L444P mutation confers genetic risk for PD, especially LOPD, among the population in the central China area.