Functional analysis of 13 GBA mutant alleles identified in Gaucher disease patients: Pathogenic changes and "modifier" polymorphisms

The lysosomal β-glucocerebrosidase strikes mitochondria: implications for Parkinson's therapeutics

Parkinson's disease is a neurodegenerative disorder primarily known for typical motor features that arise due to the loss of dopaminergic neurons in the substantia nigra. However, the precise molecular aetiology of the disease is still unclear. Several cellular pathways have been linked to Parkinson's disease, including the autophagy-lysosome pathway, α-synuclein aggregation and mitochondrial function. Interestingly, the mechanistic link between GBA1, the gene that encodes for lysosomal β-glucocerebrosidase (GCase), and Parkinson's disease lies in the interplay between GCase functions in the lysosome and mitochondria. GCase mutations alter mitochondria-lysosome contact sites. In the lysosome, reduced GCase activity leads to glycosphingolipid build-up, disrupting lysosomal function and autophagy, thereby triggering α-synuclein accumulation. Additionally, α-synuclein aggregates reduce GCase activity, creating a self-perpetuating cycle of lysosomal dysfunction and α-synuclein accumulation. GCase can also be imported into the mitochondria, where it promotes the integrity and function of mitochondrial complex I. Thus, GCase mutations that impair its normal function increase oxidative stress in mitochondria, the compartment where dopamine is oxidized. In turn, the accumulation of oxidized dopamine adducts further impairs GCase activity, creating a second cycle of GCase dysfunction. The oxidative state triggered by GCase dysfunction can also induce mitochondrial DNA damage which, in turn, can cause dopaminergic cell death. In this review, we highlight the pivotal role of GCase in Parkinson's disease pathogenesis and discuss promising examples of GCase-based therapeutics, such as gene and enzyme replacement therapies, small molecule chaperones and substrate reduction therapies, among others, as potential therapeutic interventions.

Increased glucosylsphingosine levels and Gaucher disease in GBA1-associated Parkinson's disease

INTRODUCTION

Gaucher's disease (GD) is caused by biallelic mutations in the GBA1 gene, leading to reduced glucocerebrosidase (GCase) activity and substrate (glucosylceramide and glucosylsphingosine, GlcSph) accumulation. GBA1 variant carriers are at risk of Parkinson's disease (PD), but only those with biallelic mutations cross the threshold of GCase reduction, leading to substrate accumulation and GD. The link between GBA1 mutations, GD and PD is not fully understood. Here we aimed at reporting the results of a large PD population screening with dried blood spot tests for GD.

METHODS

We measured GCase activity and GlcSph levels in 1344 PD patients with dried blood spot tests, and performed GBA1 genetic sequencing.

RESULTS

While the GCase activity was reduced in GBA1-PD carriers compared to wild type PD, GlcSph was increased in GBA1-PD compared to GBA1-controls, regardless of the underlying type of GBA1 variant. 13.6 % and 0.4 % of PD patients had mono- or biallelic GBA1 mutations respectively. GCase deficiency, lipid accumulation and clinical manifestations of GD was detected in five PD patients with biallelic GBA1 mutations, of whom four had a risk combined with a GD causing variant.

CONCLUSIONS

GlcSph appearing higher in PD may represent a reliable biomarker of the disease and deserves to be further investigated. This study highlights the importance of screening PD patients for possible underlying GD, which is a treatable condition that should not be missed. We diagnosed GD cases carrying a "risk" variant in one allele, which is an unprecedented finding deserving further investigation.

GBA1 variants in Brazilian Gaucher disease patients

Gaucher disease (GD) is an autosomal recessive lysosomal disorder caused by pathogenic variants in GBA1 which result in the deficient activity of glucocerebrosidase (GCase). There are few data on the genetic characterization of Brazilian GD patients. This study aimed at characterizing the genotype of 72 unrelated Brazilian GD patients (type I = 63, type II = 4, type III = 5; male = 31). Forty patients were from South Brazil (SB), and 32 were from other regions of Brazil (Others). The exons and exon/intron junctions of GBA1 were analyzed by Sanger sequencing in 8 patients, or by massive parallel sequencing followed by Sanger of exons 9 and 10 in 64 patients. In total, 31 pathogenic variants were identified. The most frequent allele found was N370S (p.(Asn409Ser)) (41.0%), and the most frequent genotype was N370S/RecNciI p.[Asn409Ser];[Leu483Pro;Ala495Pro;Val499=](23.6%). Three variants (N370S - in exon 9, and RecNciI and L444P (p.(Leu483Pro), in exon 10) correspond to 76.3% of total alleles in SB and 59.4% in Others. Two novel variants were described: c.326del(p.(Gln109Argfs*9)) and c.690G>A (p.(?)). Although sequencing all the exons of GBA1 is the gold-standard method for the genetic analysis of GD patients, a step analysis can be proposed for Brazilian patients, starting with analysis of exons 9 and 10. The N370S allele is the most frequently associated with GD in Brazil.

Axonal Transport of Lysosomes Is Unaffected in Glucocerebrosidase-Inhibited iPSC-Derived Forebrain Neurons

Lysosomes are acidic organelles that traffic throughout neurons delivering catabolic enzymes to distal regions of the cell and maintaining degradative demands. Loss of function mutations in the gene GBA encoding the lysosomal enzyme glucocerebrosidase (GCase) cause the lysosomal storage disorder Gaucher's disease (GD) and are the most common genetic risk factor for synucleinopathies like Parkinson's disease (PD) and dementia with Lewy bodies (DLB). GCase degrades the membrane lipid glucosylceramide (GlcCer) and mutations in GBA, or inhibiting its activity, results in the accumulation of GlcCer and disturbs the composition of the lysosomal membrane. The lysosomal membrane serves as the platform to which intracellular trafficking complexes are recruited and activated. Here, we investigated whether lysosomal trafficking in axons was altered by inhibition of GCase with the pharmacological agent Conduritol B Epoxide (CBE). Using live cell imaging in human male induced pluripotent human stem cell (iPSC)-derived forebrain neurons, we demonstrated that lysosomal transport was similar in both control and CBE-treated neurons. Furthermore, we tested whether lysosomal rupture, a process implicated in various neurodegenerative disorders, was affected by inhibition of GCase. Using L-leucyl-L-leucine methyl ester (LLoME) to induce lysosomal membrane damage and immunocytochemical staining for markers of lysosomal rupture, we found no difference in susceptibility to rupture between control and CBE-treated neurons. These results suggest the loss of GCase activity does not contribute to neurodegenerative disease by disrupting either lysosomal transport or rupture.

Glucocerebrosidase is imported into mitochondria and preserves complex I integrity and energy metabolism

Mutations in GBA1, the gene encoding the lysosomal enzyme β-glucocerebrosidase (GCase), which cause Gaucher's disease, are the most frequent genetic risk factor for Parkinson's disease (PD). Here, we employ global proteomic and single-cell genomic approaches in stable cell lines as well as induced pluripotent stem cell (iPSC)-derived neurons and midbrain organoids to dissect the mechanisms underlying GCase-related neurodegeneration. We demonstrate that GCase can be imported from the cytosol into the mitochondria via recognition of internal mitochondrial targeting sequence-like signals. In mitochondria, GCase promotes the maintenance of mitochondrial complex I (CI) integrity and function. Furthermore, GCase interacts with the mitochondrial quality control proteins HSP60 and LONP1. Disease-associated mutations impair CI stability and function and enhance the interaction with the mitochondrial quality control machinery. These findings reveal a mitochondrial role of GCase and suggest that defective CI activity and energy metabolism may drive the pathogenesis of GCase-linked neurodegeneration.

The ovine Type II Gaucher disease model recapitulates aspects of human brain disease

Acute neuronopathic (type II) Gaucher disease (GD) is a devastating, untreatable neurological disorder resulting from mutations in the glucocerebrosidase gene (GBA1), with subsequent accumulation of glucosylceramide and glucosylsphingosine. Patients experience progressive decline in neurological function, with onset typically within the first three-to-six months of life and premature death before two years. Mice and drosophila with GD have been described, however little is known about the brain pathology observed in the naturally occurring ovine model of GD. We have characterised pathological changes in GD lamb brain and compared the histological findings to those in GD patient post-mortem tissue, to determine the validity of the sheep as a model of this disease. Five GD and five age-matched unaffected lamb brains were examined. We observed significant expansion of the endo/lysosomal system in GD lamb cingulate gyrus however TPP1 and cathepsin D levels were unchanged or reduced. H&E staining revealed neurons with shrunken, hypereosinophilic cytoplasm and hyperchromatic or pyknotic nuclei (red neurons) that were also shrunken and deeply Nissl stain positive. Amoeboid microglia were noted throughout GD brain. Spheroidal inclusions reactive for TOMM20, ubiquitin and most strikingly, p-Tau were observed in many brain regions in GD lamb brain, potentially indicating disturbed axonal trafficking. Our findings suggest that the ovine model of GD exhibits similar pathological changes to human, mouse, and drosophila type II GD brain, and represents a model suitable for evaluating therapeutic intervention, particularly in utero-targeted approaches.

Development of Small Molecules Targeting α-Synuclein Aggregation: A Promising Strategy to Treat Parkinson’s Disease

Parkinson’s disease, the second most common neurodegenerative disorder worldwide, is characterized by the accumulation of protein deposits in the dopaminergic neurons. These deposits are primarily composed of aggregated forms of α-Synuclein (α-Syn). Despite the extensive research on this disease, only symptomatic treatments are currently available. However, in recent years, several compounds, mainly of an aromatic character, targeting α-Syn self-assembly and amyloid formation have been identified. These compounds, discovered by different approaches, are chemically diverse and exhibit a plethora of mechanisms of action. This work aims to provide a historical overview of the physiopathology and molecular aspects associated with Parkinson’s disease and the current trends in small compound development to target α-Syn aggregation. Although these molecules are still under development, they constitute an important step toward discovering effective anti-aggregational therapies for Parkinson’s disease.

LRRK2 and GBA1 variant carriers have higher urinary bis(monacylglycerol) phosphate concentrations in PPMI cohorts

We quantified concentrations of three isoforms of the endolysosomal lipid, bis(monoacylglycerol) phosphate (BMP) in the urine of deeply phenotyped cohorts in the Parkinson's Progression Markers Initiative: LRRK2 G2019S PD (N = 134) and non-manifesting carriers (NMC) (G2019S+ NMC; N = 182), LRRK2 R1441G PD (N = 15) and R1441G+ NMC (N = 15), GBA1 N409S PD (N = 76) and N409S+ NMC (N = 178), sporadic PD (sPD, N = 379) and healthy controls (HC) (N = 190). The effects of each mutation and disease status were analyzed using nonparametric methods. Longitudinal changes in BMP levels were analyzed using linear mixed models. At baseline, all LRRK2 carriers had 3-7× higher BMP levels compared to HC, irrespective of the disease status. GBA1 N409S carriers also showed significant, albeit smaller, elevation (~30-40%) in BMP levels compared to HC. In LRRK2 G2019S PD, urinary BMP levels remained stable over two years. Furthermore, baseline BMP levels did not predict disease progression as measured by striatal DaT imaging, MDS-UPDRS III Off, or MoCA in any of the cohorts. These data support the utility of BMP as a target modulation biomarker in therapeutic trials of genetic and sPD but not as a prognostic or disease progression biomarker.

Dietary Responses of Dementia-Related Genes Encoding Metabolic Enzymes

The age-related loss of the cognitive function is a growing concern for global populations. Many factors that determine cognitive resilience or dementia also have metabolic functions. However, this duality is not universally appreciated when the action of that factor occurs in tissues external to the brain. Thus, we examined a set of genes involved in dementia, i.e., those related to vascular dementia, Alzheimer's disease, Parkinson's disease, and the human metabolism for activity in 12 metabolically active tissues. Mining the Genotype-Tissue Expression (GTEx) data showed that most of these metabolism-dementia (MD) genes (62 of 93, 67%) exhibit a higher median expression in any of the metabolically active tissues than in the brain. After identifying that several MD genes served as blood-based biomarkers of longevity in other studies, we examined the impact of the intake of food, nutrients, and other dietary factors on the expression of MD genes in whole blood in the Framingham Offspring Study (n = 2134). We observed positive correlations between flavonoids and HMOX1, taurine and UQCRC1, broccoli and SLC10A2, and myricetin and SLC9A8 (p < 2.09 × 10-4). In contrast, dairy protein, palmitic acid, and pie were negatively correlated, respectively, with the expression of IGF1R, CSF1R, and SLC9A8, among others (p < 2.92 × 10-4). The results of this investigation underscore the potential contributions of metabolic enzyme activity in non-brain tissues to the risk of dementia. Specific epidemiological or intervention studies could be designed using specific foods and nutrients or even dietary patterns focused on these foods and nutrients that influence the expression of some MD genes to verify the findings presented here.

GBA Variants and Parkinson Disease: Mechanisms and Treatments

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

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.

Clinical phenotype features and genetic etiologies of 38 children with progressive myoclonic epilepsy

Background

Progressive myoclonic epilepsy (PME) is a group of neurodegenerative diseases with genetic heterogeneity and phenotypic similarities, and many cases remain unknown of the genetic causes. This study is aim to summarize the clinical features and study the genetic causes of PME patients.

Methods

Sanger sequencing of the target gene, Next Generation Sequencing (NGS) panels of epilepsy, trio-based Whole Exome Sequencing (WES) and detection of cytosine-adenine-guanine (CAG) repeat number were used to investigate the genetic causes of PME patients.

Results

Thirty-eight children with PME whose seizure onset age ranged from 3 months to 12 years were collected from February 2012 to November 2019 in three hospitals in Beijing, China. The seizure types included myoclonic seizures (n = 38), focal seizures (n = 19), generalized tonic-clonie seizure (GTCS) (n = 13), absence seizures (n = 4), atonic seizures (n = 3), epileptic spasms (n = 2) and tonic seizures (n = 1). Twenty-seven cases were sporadic and 11 had family members affected. Established PME-related genes were identified in 30 out of 38 (78.9%) patients who had either recessively inherited or de novo heterozygous mutations. Among these 30 cases, there were 12 cases (31.6%) of neuronal ceroid lipofuscinoses (the causing gene contains TPP1, PPT1, CLN5, CLN6 and MFSD8), two cases of sialidosis (the causing gene is NEU1), two cases of neuronopathic Gaucher disease (the causing gene is GBA), one case of spinal muscular atrophy-progressive myoclonic epilepsy (the causing gene is ASAH1), four cases of KCNC1 mutation-related PME, four cases of KCTD7 mutation-related PME, two cases of TBC1D24 mutation-related PME, one case of GOSR2 related PME, and two of dentatorubral-pallidoluysian atrophy (the causing gene is ATN1). In total, 13 PME genes were identified in our cohort. The etiology was not clear in eight patients.

Conclusion

PME is a group of clinically and genetically heterogeneous diseases. Genetic diagnosis was clear in 78.9% of PME patients. Various of genetic testing methods could increase the rate of genetic diagnosis. Neuronal ceroid lipofuscinoses (NCL) is the most common etiology of PME in children. Nearly one third PME children were diagnosed with NCL. GOSR2 related PME was in our cohort in Asia for the first time.

A Quantitative Systems Pharmacology Model of Gaucher Disease Type 1 Provides Mechanistic Insight Into the Response to Substrate Reduction Therapy With Eliglustat

Gaucher’s disease type 1 (GD1) leads to significant morbidity and mortality through clinical manifestations, such as splenomegaly, hematological complications, and bone disease. Two types of therapies are currently approved for GD1: enzyme replacement therapy (ERT), and substrate reduction therapy (SRT). In this study, we have developed a quantitative systems pharmacology (QSP) model, which recapitulates the effects of eliglustat, the only first‐line SRT approved for GD1, on treatment‐naïve or patients with ERT‐stabilized adult GD1. This multiscale model represents the mechanism of action of eliglustat that leads toward reduction of spleen volume. Model capabilities were illustrated through the application of the model to predict ERT and eliglustat responses in virtual populations of adult patients with GD1, representing patients across a spectrum of disease severity as defined by genotype‐phenotype relationships. In summary, the QSP model provides a mechanistic computational platform for predicting treatment response via different modalities within the heterogeneous GD1 patient population.

Parkinson's disease in a patient with multiple sclerosis and heterozygous glucocerebrosidase gene mutation

More than 30 patients with multiple sclerosis (MS) and Parkinson's disease (PD) have been reported so far. Theories on the co-occurrence of MS and PD range from coincidental to causal. There has been only one report of MS in young onset PD in a patient heterozygous for Parkin mutation. We report a patient with MS who developed signs typical for PD and was found to be heterozygous mutation carrier in the gene for glucocerebrosidase (GBA1), a well-known risk factor for PD.

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We report a case of MS patient who developed PD and was found to be heterozygous carrier of GBA1 gene mutation.

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MS might increase the chances of PD development in GBA1 gene mutation carriers.

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The mechanisms by which GBA1 mutations increase the risk of development PD in the setting of MS are not known.

Nanopore sequencing of the glucocerebrosidase (GBA) gene in a New Zealand Parkinson's disease cohort

INTRODUCTION

Bi-allelic mutations in the gene for glucocerebrosidase (GBA) cause Gaucher disease, an autosomal recessive lysosomal storage disorder. Gaucher disease causing GBA mutations in the heterozygous state are also high risk factors for Parkinson's disease (PD). GBA analysis is challenging due to a related pseudogene and structural variations (SVs) that can occur at this locus. We have applied and refined a recently developed nanopore DNA sequencing method to analyze GBA variants in a clinically assessed New Zealand longitudinal cohort of PD.

METHOD

We examined amplicons encompassing the coding region of GBA (8.9 kb) from 229 PD cases and 50 healthy controls using the GridION nanopore sequencing platform, and Sanger validation.

RESULTS

We detected 23 variants in 21 PD cases (9.2% of patients). We detected modest PD risk variant p.N409S (rs76763715) in one case, p.E365K (rs2230288) in 12 cases, and p.T408 M (rs75548401) in seven cases, one of whom also had p.E365K. We additionally detected the possible risk variants p.R78C (rs146774384) in one case, p.D179H (rs147138516) in one case which occurred on the same haplotype as p.E365K, and one novel variant c.335C > T or p.(L335 = ), that potentially impacts splicing of GBA transcripts. Additionally, we found a higher prevalence of dementia among patients with GBA variants.

CONCLUSION

This work confirmed the utility of nanopore sequencing as a high-throughput method to identify known and novel GBA variants, and to assign precise haplotypes. Our observations may contribute to improved understanding of the effects of variants on disease pathogenesis, and to the development of more targeted treatments.

The role of monogenic genes in idiopathic Parkinson's disease

In the past two decades, mutations in multiple genes have been linked to autosomal dominant or recessive forms of monogenic Parkinson's disease (PD). Collectively, these monogenic (often familial) cases account for less than 5% of all PD, the majority being apparently sporadic cases. More recently, large-scale genome-wide association studies have identified over 40 loci that increase risk of PD. Importantly, there is overlap between monogenic and sporadic PD genes, particularly for the loci that contain the genes SNCA and LRRK2, which are mutated in monogenic dominant PD. There have also been reports of idiopathic PD cases with heterozygous variants in autosomal recessive genes suggesting that these mutations may increase risk of PD. These observations suggest that monogenic and idiopathic PD may have shared pathogenic mechanisms. Here, we focus mainly on the role of monogenic PD genes that represent pleomorphic risk loci for idiopathic PD. We also discuss the functional mechanisms that may play a role in increasing risk of disease in both monogenic and idiopathic forms.

Progressive myoclonus epilepsy in Gaucher Disease due to a new Gly-Gly mutation causing loss of an Exonic Splicing Enhancer

BACKGROUND

Patients with Gaucher Disease (GD) exhibit three phenotypes, including type 1 (non-neuronopathic), type 2 (acute neuronopathic), and type 3 (subacute neuronopathic).

AIM

Identifying which GBA changes represent benign polymorphisms and which may result in disease-causing mutations is essential for diagnosis and genotype/phenotype correlations but is often challenging.

RESULTS

Here, we describe a patient with type 3 GD, presenting with drug-resistant epilepsy, who bears a set of GBA polymorphic variants including the novel c.363A > G (Gly82Gly) synonymous mutation. In silico predictions, mRNA and functional studies revealed that the new Gly82Gly mutation causes skipping of GBA exon 4, leading to a severe reduction of the wild type GBA mRNA. This is the first report of a synonymous change causing GD through loss of an exonic splicing enhancer sequence. The synonymous mutation is in trans with the Asn188Ser missense mutation, thus making the Asn188Ser responsible for the patient's phenotype and strengthening the association of Asn188Ser with the particular neurological phenotype of type 3 GD.

CONCLUSION

We strengthen the association of Asn188Ser with the type 3 GD phenotype and progressive myoclonus epilepsy. Our data confirm that in silico predictions and mRNA analysis are mandatory in discriminating pathological mutations from the background of harmless polymorphisms, especially synonymous changes.

In Silico Analysis of Missense Mutations as a First Step in Functional Studies: Examples from Two Sphingolipidoses

In order to delineate a better approach to functional studies, we have selected 23 missense mutations distributed in different domains of two lysosomal enzymes, to be studied by in silico analysis. In silico analysis of mutations relies on computational modeling to predict their effects. Various computational platforms are currently available to check the probable causality of mutations encountered in patients at the protein and at the RNA levels. In this work we used four different platforms freely available online (Protein Variation Effect Analyzer- PROVEAN, PolyPhen-2, Swiss-model Expert Protein Analysis System—ExPASy, and SNAP2) to check amino acid substitutions and their effect at the protein level. The existence of functional studies, regarding the amino acid substitutions, led to the selection of the distinct protein mutants. Functional data were used to compare the results obtained with different bioinformatics tools. With the advent of next-generation sequencing, it is not feasible to carry out functional tests in all the variants detected. In silico analysis seems to be useful for the delineation of which mutants are worth studying through functional studies. Therefore, prediction of the mutation impact at the protein level, applying computational analysis, confers the means to rapidly provide a prognosis value to genotyping results, making it potentially valuable for patient care as well as research purposes. The present work points to the need to carry out functional studies in mutations that might look neutral. Moreover, it should be noted that single nucleotide polymorphisms (SNPs), occurring in coding and non-coding regions, may lead to RNA alterations and should be systematically verified. Functional studies can gain from a preliminary multi-step approach, such as the one proposed here.

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.

Association of glucocerebrosidase polymorphisms and mutations with dementia in incident Parkinson's disease

INTRODUCTION

Both polymorphisms and mutations in glucocerebrosidase (GBA) may influence the development of dementia in patients with Parkinson's disease.

METHODS

Four hundred forty-two patients and 419 controls were followed for 7 years. Dementia was diagnosed using established criteria. Participants were analyzed for GBA genetic variants, including E326K, T369M, and L444P. Associations between GBA carrier status and dementia were assessed with Cox survival analysis.

RESULTS

A total of 12.0% of patients with Parkinson's disease carried a GBA variant, and nearly half (22/53) of them progressed to dementia during follow-up. Carriers of deleterious GBA mutations (adjusted hazard ratio 3.81, 95% confidence interval 1.35 to 10.72; P = .011) or polymorphisms (adjusted hazard ratio 1.79; 95% confidence interval 1.07 to 3.00; P = .028) progressed to dementia more rapidly than noncarriers.

DISCUSSION

GBA variants are of great clinical relevance for the development of dementia in Parkinson's disease, especially due to the relatively higher frequency of these alleles compared with other risk alleles.

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.

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.

Large-scale exploratory genetic analysis of cognitive impairment in Parkinson's disease

Cognitive impairment is a common and disabling problem in Parkinson's disease (PD). Identification of genetic variants that influence the presence or severity of cognitive deficits in PD might provide a clearer understanding of the pathophysiology underlying this important nonmotor feature. We genotyped 1105 PD patients from the PD Cognitive Genetics Consortium for 249,336 variants using the NeuroX array. Participants underwent assessments of learning and memory (Hopkins Verbal Learning Test-Revised [HVLT-R]), working memory/executive function (Letter-Number Sequencing and Trail Making Test [TMT] A and B), language processing (semantic and phonemic verbal fluency), visuospatial abilities (Benton Judgment of Line Orientation [JoLO]), and global cognitive function (Montreal Cognitive Assessment). For common variants, we used linear regression to test for association between genotype and cognitive performance with adjustment for important covariates. Rare variants were analyzed using the optimal unified sequence kernel association test. The significance threshold was defined as a false discovery rate-corrected p-value (P_FDR) of 0.05. Eighteen common variants in 13 genomic regions exceeded the significance threshold for one of the cognitive tests. These included GBA rs2230288 (E326K; P_FDR = 2.7 × 10^-4) for JoLO, PARP4 rs9318600 (P_FDR = 0.006), and rs9581094 (P_FDR = 0.006) for HVLT-R total recall, and MTCL1 rs34877994 (P_FDR = 0.01) for TMT B-A. Analysis of rare variants did not yield any significant gene regions. We have conducted the first large-scale PD cognitive genetics analysis and nominated several new putative susceptibility genes for cognitive impairment in PD. These results will require replication in independent PD cohorts.

Successful newborn screening for Gaucher disease using fluorometric assay in China

Gaucher disease (GD) is an inherited metabolic disorder that involves accumulation of glycolipid glucocerebroside in monocyte–macrophage cells, which can result in multiple organ damage. Enzyme replacement and substrate reduction therapies have improved the potential for early diagnosis and treatment. Determining the true incidence of this rare disease is critical for relevant policy establishment. Newborn screening allows for early diagnosis and an comparatively accurate incidence of GD. A fluorometric method to detect acid β-glucocerebrosidase (GBA) activity on a dried blood spot punch was developed. Validity and feasibility of the fluorometric method was demonstrated by examining 116 healthy controls, 19 confirmed GD patients and 19 obligate carriers. GBA activity was measured on dried blood spots of 80 855 newborns. Samples from positively screened newborns were reanalyzed by a leukocyte GBA activity test and GBA gene analysis. Plasma glucosylsphingosine level was determined as a biomarker of the pathophysiology of GD. GD patients were distinguished from healthy controls and obligate carriers using the fluorometric method. Mean GBA activity in newborn screening specimens was 145.69±44.76 μmol l⁻¹ h⁻¹ (n=80 844). Three children had low GBA activity, of which one child had low GBA activity on the second dried blood spot specimen. Leukocyte, genetic and biomarker analysis confirmed the diagnosis and indicated that this child was in the early stages of GD. In conclusion, the incidence of GD in Shanghai of China is approximately 1 in 80 855. Screening for GD by fluorometric analysis of GBA activity is an efficient and feasible technology in newborns.

Genetics of Parkinson's Disease: Genotype-Phenotype Correlations

Since the first discovery of a specific genetic defect in the SNCA gene, encoding for α-synuclein, as a causative factor for Parkinson's disease 20 years ago, a multitude of other genes have been linked to this disease in rare cases with Mendelian inheritance. Furthermore, the genetic contribution to the much more common sporadic disease has been demonstrated through case control association studies and, more recently, genome-wide association studies. Interestingly, some of the genes with Mendelian inheritance, such as SNCA, are also relevant to the sporadic disease, suggesting common pathogenetic mechanisms. In this review, we place an emphasis on Mendelian forms, and in particular genetic defects which present predominantly with Parkinsonism. We provide details into the particular phenotypes associated with each genetic defect, with a particular emphasis on nonmotor symptoms. For genetic defects for whom a sufficient number of patients has been assessed, there are evident genotype-phenotype correlations. However, it should be noted that patients with the same causative mutation may present with distinctly divergent phenotypes. This phenotypic variability may be due to genetic, epigenetic or environmental factors. From a clinical and genetic point of view, it will be especially interesting in the future to identify genetic factors that modify disease penetrance, the age of onset or other specific phenotypic features.

The emerging role of autophagic-lysosomal dysfunction in Gaucher disease and Parkinson's disease

Gaucher disease (GD), the commonest lysosomal storage disorder, results from the lack or functional deficiency of glucocerebrosidase (GCase) secondary to mutations in the GBA1 gene. There is an established association between GBA1 mutations and Parkinson's disease (PD), and indeed GBA1 mutations are now considered to be the greatest genetic risk factor for PD. Impaired lysosomal-autophagic degradation of cellular proteins, including α-synuclein (α-syn), is implicated in the pathogenesis of PD, and there is increasing evidence for this also in GD and GBA1-PD. Indeed we have recently shown in a Drosophila model lacking neuronal GCase, that there are clear lysosomal-autophagic defects in association with synaptic loss and neurodegeneration. In addition, we demonstrated alterations in mechanistic target of rapamycin complex 1 (mTORC1) signaling and functional rescue of the lifespan, locomotor defects and hypersensitivity to oxidative stress on treatment of GCase-deficient flies with the mTOR inhibitor rapamycin. Moreover, a number of other recent studies have shown autophagy-lysosomal system (ALS) dysfunction, with specific defects in both chaperone-mediated autophagy (CMA), as well as macroautophagy, in GD and GBA1-PD model systems. Lastly we discuss the possible therapeutic benefits of inhibiting mTOR using drugs such as rapamycin to reverse the autophagy defects in GD and PD.

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.

A Novel Functional Missense Mutation p.T219A in Type 1 Gaucher's Disease

Background:

Gaucher's disease (GD) is an autosomal recessive disorder caused by a deficiency of acid β-glucosidase (glucocerebrosidase [GBA]) that results in the accumulation of glucocerebroside within macrophages. Many mutations have been reported to be associated with this disorder. This study aimed to discover more mutations and provide data for the genetic pattern of the gene, which will help the development of quick and accurate genetic diagnostic tools for this disease.

Methods:

Genomic DNA was obtained from peripheral blood leukocytes of the patient and Sanger sequencing is used to sequence GBA gene. Sequence alignments of mammalian β-GBA (GCase) and three-dimensional protein structure prediction of the mutation were made. A construct of this mutant and its compound heterozygous counterpart were used to measure GCase in vitro.

Results:

GCase is relatively conserved at p.T219A. This novel mutation differs from its wild-type in structure. Moreover, it also causes a reduction in GCase enzyme activity.

Conclusion:

This novel mutation (c.655A>G, p.T219A) is a pathogenic missense mutation, which contributes to GD.

Strong association between glucocerebrosidase mutations and Parkinson's disease in Sweden

Several genetic studies have demonstrated an association between mutations in glucocerebrosidase (GBA), originally implicated in Gaucher's disease, and an increased risk of Parkinson's disease (PD). We have investigated the possible involvement of genetic GBA variations in PD in the Swedish population. Three GBA variants, E326K, N370S, and L444P were screened in the largest Swedish Parkinson cohort reported to date; 1625 cases and 2025 control individuals. We found a significant association with high effect size of the rare variant L444P with PD (odds ratio 8.17; 95% confidence interval: 2.51-26.23; p-value = 0.0020) and a significant association of the common variant E326K (odds ratio 1.60; 95% confidence interval: 1.16-2.22; p-value = 0.026). The rare variant N370S showed a trend for association. Most L444P carriers (68%) were found to reside in northern Sweden, which is consistent with a higher prevalence of Gaucher's disease in this part of the country. Our findings support the role of GBA mutations as risk factors for PD and point to lysosomal dysfunction as a mechanism contributing to PD etiology.

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.

Synchronous Hepatoblastoma, Neuroblastoma, and Cutaneous Capillary Hemangiomas: A Case Report

Multiple synchronous tumors presenting in infancy raise concern for inherited or sporadic cancer predisposition syndromes, which include Beckwith-Wiedemann syndrome, familial adenomatous polyposis syndrome, and Li-Fraumeni syndrome. We report a case of a 7-month-old previously healthy male born following an in vitro fertilization-assisted twin pregnancy who presented with new-onset refractory shock, severe acidosis, and rapid decline over several hours. An autopsy revealed a ruptured liver involved by hepatoblastoma, an adrenal gland involved by neuroblastoma, and multiple cutaneous capillary hemangiomas. Standard genetic testing demonstrated that both twins were Gaucher disease (GD) carriers without evidence of other known cancer predisposition syndromes. This report describes a unique association of multiple synchronous tumors, which underscores the utility and importance of the pediatric autopsy. Moreover, given that the reported child was a GD carrier, the possibility the tumors were the result of a GD-mediated cancer-associated phenotype or an unrecognized sporadic clinical syndrome remains an unanswered, but intriguing, question worthy of further investigation.

GBA Variants are associated with a distinct pattern of cognitive deficits in Parkinson's disease

BACKGROUND

Loss-of-function mutations in the GBA gene are associated with more severe cognitive impairment in PD, but the nature of these deficits is not well understood and whether common GBA polymorphisms influence cognitive performance in PD is not yet known.

METHODS

We screened the GBA coding region for mutations and the E326K polymorphism in 1,369 PD patients enrolled at eight sites from the PD Cognitive Genetics Consortium. Participants underwent assessments of learning and memory (Hopkins Verbal Learning Test-Revised), working memory/executive function (Letter-Number Sequencing Test and Trail Making Test A and B), language processing (semantic and phonemic verbal fluency), visuospatial abilities (Benton Judgment of Line Orientation), and global cognitive function (MoCA). We used linear regression to test for association between genotype and cognitive performance with adjustment for important covariates and accounted for multiple testing using Bonferroni's corrections.

RESULTS

Mutation carriers (n = 60; 4.4%) and E326K carriers (n = 65; 4.7%) had a higher prevalence of dementia (mutations, odds ratio = 5.1; P = 9.7 × 10(-6) ; E326K, odds ratio = 6.4; P = 5.7 × 10(-7) ) and lower performance on Letter-Number Sequencing (mutations, corrected P[Pc ] = 9.0 × 10(-4) ; E326K, Pc  = 0.036), Trail Making B-A (mutations, Pc  = 0.018; E326K, Pc  = 0.018), and Benton Judgment of Line Orientation (mutations, Pc  = 0.0045; E326K, Pc  = 0.0013).

CONCLUSIONS

Both GBA mutations and E326K are associated with a distinct cognitive profile characterized by greater impairment in working memory/executive function and visuospatial abilities in PD patients. The discovery that E326K negatively impacts cognitive performance approximately doubles the proportion of PD patients we now recognize are at risk for more severe GBA-related cognitive deficits.

Sustained Systemic Glucocerebrosidase Inhibition Induces Brain α-Synuclein Aggregation, Microglia and Complement C1q Activation in Mice

AIMS

Loss-of-function mutations in GBA1, which cause the autosomal recessive lysosomal storage disease, Gaucher disease (GD), are also a key genetic risk factor for the α-synucleinopathies, including Parkinson's disease (PD) and dementia with Lewy bodies. GBA1 encodes for the lysosomal hydrolase glucocerebrosidase and reductions in this enzyme result in the accumulation of the glycolipid substrates glucosylceramide and glucosylsphingosine. Deficits in autophagy and lysosomal degradation pathways likely contribute to the pathological accumulation of α-synuclein in PD. In this report we used conduritol-β-epoxide (CBE), a potent selective irreversible competitive inhibitor of glucocerebrosidase, to model reduced glucocerebrosidase activity in vivo, and tested whether sustained glucocerebrosidase inhibition in mice could induce neuropathological abnormalities including α-synucleinopathy, and neurodegeneration.

RESULTS

Our data demonstrate that daily systemic CBE treatment over 28 days caused accumulation of insoluble α-synuclein aggregates in the substantia nigra, and altered levels of proteins involved in the autophagy lysosomal system. These neuropathological changes were paralleled by widespread neuroinflammation, upregulation of complement C1q, abnormalities in synaptic, axonal transport and cytoskeletal proteins, and neurodegeneration.

INNOVATION

A reduction in brain GCase activity has been linked to sporadic PD and normal aging, and may contribute to the susceptibility of vulnerable neurons to degeneration. This report demonstrates that systemic reduction of GCase activity using chemical inhibition, leads to neuropathological changes in the brain reminiscent of α-synucleinopathy.

CONCLUSIONS

These data reveal a link between reduced glucocerebrosidase and the development of α-synucleinopathy and pathophysiological abnormalities in mice, and support the development of GCase therapeutics to reduce α-synucleinopathy in PD and related disorders.

No evidence for substrate accumulation in Parkinson brains with GBA mutations

BACKGROUND

To establish whether Parkinson's disease (PD) brains previously described to have decreased glucocerebrosidase activity exhibit accumulation of the lysosomal enzyme's substrate, glucosylceramide, or other changes in lipid composition.

METHODS

Lipidomic analyses and cholesterol measurements were performed on the putamen (n = 5-7) and cerebellum (n = 7-14) of controls, Parkinson's disease brains with heterozygote GBA1 mutations (PD+GBA), or sporadic PD.

RESULTS

Total glucosylceramide levels were unchanged in both PD+GBA and sporadic PD brains when compared with controls. No changes in glucosylsphingosine (deacetylated glucosylceramide), sphingomyelin, gangliosides (GM2, GM3), or total cholesterol were observed in either putamen or cerebellum.

CONCLUSIONS

This study did not demonstrate glucocerebrosidase substrate accumulation in PD brains with heterozygote GBA1 mutations in areas of the brain with low α-synuclein pathology.

Understanding carbamoyl phosphate synthetase (CPS1) deficiency by using the recombinantly purified human enzyme: effects of CPS1 mutations that concentrate in a central domain of unknown function

Carbamoyl phosphate synthetase 1 deficiency (CPS1D) is an inborn error of the urea cycle that is due to mutations in the CPS1 gene. In the first large repertory of mutations found in CPS1D, a small CPS1 domain of unknown function (called the UFSD) was found to host missense changes with high frequency, despite the fact that this domain does not host substrate-binding or catalytic machinery. We investigate here by in vitro expression studies using baculovirus/insect cells the reasons for the prominence of the UFSD in CPS1D, as well as the disease-causing roles and pathogenic mechanisms of the mutations affecting this domain. All but three of the 18 missense changes found thus far mapping in this domain in CPS1D patients drastically decreased the yield of pure CPS1, mainly because of decreased enzyme solubility, strongly suggesting misfolding as a major determinant of the mutations negative effects. In addition, the majority of the mutations also decreased from modestly to very drastically the specific activity of the fraction of the enzyme that remained soluble and that could be purified, apparently because they decreased V(max). Substantial although not dramatic increases in K(m) values for the substrates or for N-acetyl-L-glutamate were observed for only five mutations. Similarly, important thermal stability decreases were observed for three mutations. The results indicate a disease-causing role for all the mutations, due in most cases to the combined effects of the low enzyme level and the decreased activity. Our data strongly support the value of the present expression system for ascertaining the disease-causing potential of CPS1 mutations, provided that the CPS1 yield is monitored. The observed effects of the mutations have been rationalized on the basis of an existing structural model of CPS1. This model shows that the UFSD, which is in the middle of the 1462-residue multidomain CPS1 protein, plays a key integrating role for creating the CPS1 multidomain architecture leading us to propose here a denomination of "Integrating Domain" for this CPS1 region. The majority of these 18 mutations distort the interaction of this domain with other CPS1 domains, in many cases by causing improper folding of structural elements of the Integrating Domain that play key roles in these interactions.

Glucocerebrosidase is shaking up the synucleinopathies

The lysosomal enzyme glucocerebrosidase, encoded by the glucocerebrosidase gene, is involved in the breakdown of glucocerebroside into glucose and ceramide. Lysosomal build-up of the substrate glucocerebroside occurs in cells of the reticulo-endothelial system in patients with Gaucher disease, a rare lysosomal storage disorder caused by the recessively inherited deficiency of glucocerebrosidase. Gaucher disease has a broad clinical phenotypic spectrum, divided into non-neuronopathic and neuronopathic forms. Like many monogenic diseases, the correlation between clinical manifestations and molecular genotype is not straightforward. There is now a well-established clinical association between mutations in the glucocerebrosidase gene and the development of more prevalent multifactorial disorders including Parkinson's disease and other synucleinopathies. In this review we discuss recent studies advancing our understanding of the cellular relationship between glucocerebrosidase and α-synuclein, the potential impact of established and emerging therapeutics for Gaucher disease for the treatment of the synucleinopathies, and the role of lysosomal pathways in the pathogenesis of these neurodegenerative disorders.

Reduced glucocerebrosidase is associated with increased α-synuclein in sporadic Parkinson's disease

Heterozygous mutations in GBA1, the gene encoding lysosomal glucocerebrosidase, are the most frequent known genetic risk factor for Parkinson's disease. Reduced glucocerebrosidase and α-synuclein accumulation are directly related in cell models of Parkinson's disease. We investigated relationships between Parkinson's disease-specific glucocerebrosidase deficits, glucocerebrosidase-related pathways, and α-synuclein levels in brain tissue from subjects with sporadic Parkinson's disease without GBA1 mutations. Brain regions with and without a Parkinson's disease-related increase in α-synuclein levels were assessed in autopsy samples from subjects with sporadic Parkinson's disease (n = 19) and age- and post-mortem delay-matched controls (n = 10). Levels of glucocerebrosidase, α-synuclein and related lysosomal and autophagic proteins were assessed by western blotting. Glucocerebrosidase enzyme activity was measured using a fluorimetric assay, and glucocerebrosidase and α-synuclein messenger RNA expression determined by quantitative polymerase chain reaction. Related sphingolipids were analysed by mass spectrometry. Multivariate statistical analyses were performed to identify differences between disease groups and regions, with non-parametric correlations used to identify relationships between variables. Glucocerebrosidase protein levels and enzyme activity were selectively reduced in the early stages of Parkinson's disease in regions with increased α-synuclein levels although limited inclusion formation, whereas GBA1 messenger RNA expression was non-selectively reduced in Parkinson's disease. The selective loss of lysosomal glucocerebrosidase was directly related to reduced lysosomal chaperone-mediated autophagy, increased α-synuclein and decreased ceramide. Glucocerebrosidase deficits in sporadic Parkinson's disease are related to the abnormal accumulation of α-synuclein and are associated with substantial alterations in lysosomal chaperone-mediated autophagy pathways and lipid metabolism. Our data suggest that the early selective Parkinson's disease changes are likely a result of the redistribution of cellular membrane proteins leading to a chronic reduction in lysosome function in brain regions vulnerable to Parkinson's disease pathology.

Functional analysis of 11 novel GBA alleles

Gaucher disease is the most frequent lysosomal storage disorder due to the deficiency of the acid β-glucosidase, encoded by the GBA gene. In this study, we report the structural and functional characterization of 11 novel GBA alleles. Seven single missense alleles, P159S, N188I, E235K, P245T, W312S, S366R and W381C, and two alleles carrying in cis mutations, (N188S; G265R) and (E326K; D380N), were studied for enzyme activity in transiently transfected cells. All mutants were inactive except the P159S, which retained 15% of wild-type activity. To further characterize the alleles carrying two in cis mutations, we expressed constructs bearing singly each mutation. The presence of G265R or D380N mutations completely abolished enzyme activity, while N188S and E326K mutants retained 25 and 54% of wild-type activity, respectively. Two mutations, affecting the acceptor splice site of introns 5 (c.589-1G>A) and 9 (c.1389-1G>A), led to the synthesis of aberrant mRNA. Unpredictably, family studies showed that two alleles resulted from germline or 'de novo' mutations. These results strengthen the importance of performing a complete and accurate molecular analysis of the GBA gene in order to avoid misleading conclusions and provide a comprehensive functional analysis of new GBA mutations.

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.

Sequence and copy number analyses of HEXB gene in patients affected by Sandhoff disease: functional characterization of 9 novel sequence variants

Sandhoff disease (SD) is a lysosomal disorder caused by mutations in the HEXB gene. To date, 43 mutations of HEXB have been described, including 3 large deletions. Here, we have characterized 14 unrelated SD patients and developed a Multiplex Ligation-dependent Probe Amplification (MLPA) assay to investigate the presence of large HEXB deletions. Overall, we identified 16 alleles, 9 of which were novel, including 4 sequence variation leading to aminoacid changes [c.626C>T (p.T209I), c.634C>A (p.H212N), c.926G>T (p.C309F), c.1451G>A (p.G484E)] 3 intronic mutations (c.1082+5G>A, c.1242+1G>A, c.1169+5G>A), 1 nonsense mutation c.146C>A (p.S49X) and 1 small in-frame deletion c.1260_1265delAGTTGA (p.V421_E422del). Using the new MLPA assay, 2 previously described deletions were identified. In vitro expression studies showed that proteins bearing aminoacid changes p.T209I and p.G484E presented a very low or absent activity, while proteins bearing the p.H212N and p.C309F changes retained a significant residual activity. The detrimental effect of the 3 novel intronic mutations on the HEXB mRNA processing was demonstrated using a minigene assay. Unprecedentedly, minigene studies revealed the presence of a novel alternative spliced HEXB mRNA variant also present in normal cells. In conclusion, we provided new insights into the molecular basis of SD and validated an MLPA assay for detecting large HEXB deletions.

The role of saposin C in Gaucher disease

Saposin C is one of four homologous proteins derived from sequential cleavage of the saposin precursor protein, prosaposin. It is an essential activator for glucocerebrosidase, the enzyme deficient in Gaucher disease. Gaucher disease is a rare autosomal recessive lysosomal storage disorder caused by mutations in the GBA gene that exhibits vast phenotypic heterogeneity, despite its designation as a "simple" Mendelian disorder. The observed phenotypic variability has led to a search for disease modifiers that can alter the Gaucher phenotype. The PSAP gene encoding saposin C is a prime candidate modifier for Gaucher disease. In humans, saposin C deficiency due to mutations in PSAP results in a Gaucher-like phenotype, despite normal in vitro glucocerebrosidase activity. Saposin C deficiency has also been shown to modify phenotype in one mouse model of Gaucher disease. The role of saposin C as an activator required for normal glucocerebrosidase function, and the consequences of saposin C deficiency are described, and are being explored as potential modifying factors in patients with Gaucher disease.

Newborn screening for lysosomal storage disorders in hungary

Even though lysosomal storage disorders (LSDs) are considered to be orphan diseases, they pose a highly relevant cause for morbidity and mortality as their cumulative prevalence is estimated to be 1:4,000. This is especially important as treatment in form of enzyme replacement therapy, substrate reduction therapy or stem cell transplantation is amenable for some LSDs. It is plausible that an early start of treatment might improve the overall prognosis and, even more important, prevent irreversible damage of key organs. To get a more precise insight into the real frequency of some LSDs in the general population, we screened 40,024 samples from the Hungarian newborn screening (NBS) program in Szeged for Fabry disease (FD), Gaucher disease (GD), Pompe disease (PD), and Niemann-Pick A/B (NPB) disease using tandem mass spectrometry. Altogether, 663 samples (1.66%) were submitted for retesting. Genetic confirmation was carried out for 120 samples with abnormal screening results after retesting, which identified three cases of GD, three cases of FD, nine cases of PD, and two cases with NPB. In some cases, we detected up to now unknown mutations - one in NPB and seven in PD - which raise questions about the clinical consequences of a NBS in the sense of late-onset manifestations. Overall, we conclude that screening for LSDs by tandem MS/MS followed by a genetic workup in identified patients is a robust, easy, valid, and feasible technology in newborn screening programs. Furthermore, early diagnosis of LSDs gives a chance to early treatment, but needs more clinical long-term data especially regarding the consequence of private mutations.

The enigma of the E326K mutation in acid β-glucocerebrosidase

A large number of mutations, and several polymorphisms, have been characterized in the GBA gene, encoding the lysosomal enzyme glucocerebrosidase, the activity of which is impaired in Gaucher disease. In this communication we summarize published and new data concerning biochemical characterization of the E326K amino acid change (1093G>A in the GBA1 cDNA) in tissue culture and its association with Parkinson disease, suggesting it is a disease causing mutation and not merely a polymorphism in the GBA gene.

Molecular basis of reduced glucosylceramidase activity in the most common Gaucher disease mutant, N370S

Gaucher disease is caused by the defective activity of the lysosomal hydrolase, glucosylceramidase. Although the x-ray structure of wild type glucosylceramidase has been resolved, little is known about the structural features of any of the >200 mutations. Various treatments for Gaucher disease are available, including enzyme replacement and chaperone therapies. The latter involves binding of competitive inhibitors at the active site to enable correct folding and transport of the mutant enzyme to the lysosome. We now use molecular dynamics, a set of structural analysis tools, and several statistical methods to determine the flexible behavior of the N370S Gaucher mutant at various pH values, with and without binding the chaperone, N-butyl-deoxynojirimycin. We focus on the effect of the chaperone on the whole protein, on the active site, and on three important structural loops, and we demonstrate how the chaperone modifies the behavior of N370S in such a way that it becomes more active at lysosomal pH. Our results suggest a mechanism whereby the binding of N-butyl-deoxynojirimycin helps target correctly folded glucosylceramidase to the lysosome, contributes to binding with saposin C, and explains the initiation of the substrate-enzyme complex. Such analysis provides a new framework for determination of the structure of other Gaucher disease mutants and suggests new approaches for rational drug design.