The incidence of Parkinsonism in patients with type 1 Gaucher disease: data from the ICGG Gaucher Registry

Skin α-Synuclein Seeding Activity in Patients with Type 1 Gaucher Disease

BACKGROUND

Patients with type 1 Gaucher disease (GD1) have a significantly increased risk of developing Parkinson's disease (PD).

OBJECTIVE

The objective of this study was to evaluate skin α-synuclein (αSyn) seeding activity as a biomarker for GD1-related PD (GD1-PD).

METHODS

This single-center study administered motor and cognitive examinations and questionnaires of nonmotor symptoms to adult patients with GD1. Optional skin biopsy was performed for skin αSyn seed amplification assay (αSyn SAA) using real-time quaking-induced conversion assay.

RESULTS

Forty-nine patients were enrolled, and 36 underwent skin biopsy. Two study participants had PD. Ten participants were αSyn SAA positive (27.8%), 7 (19.4%) were intermediate, and 19 (52.8%) were negative. Positive αSyn seeding activity was observed in the single GD1-PD case who consented to biopsy. αSyn SAA positivity was associated with older age (p = 0.043), although αSyn SAA positivity was more prevalent in patients with GD1 than historic controls.

CONCLUSIONS

Longitudinal follow-up is required to determine whether skin αSyn seeding activity can be an early biomarker for GD1-PD. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

High-throughput screening for small-molecule stabilizers of misfolded glucocerebrosidase in Gaucher disease and Parkinson's disease

Glucocerebrosidase (GCase) is implicated in both a rare, monogenic disorder (Gaucher disease, GD) and a common, multifactorial condition (Parkinson's disease, PD); hence, it is an urgent therapeutic target. To identify correctors of severe protein misfolding and trafficking obstruction manifested by the pathogenic L444P-variant of GCase, we developed a suite of quantitative, high-throughput, cell-based assays. First, we labeled GCase with a small proluminescent HiBiT peptide reporter tag, enabling quantitation of protein stabilization in cells while faithfully maintaining target biology. TALEN-based gene editing allowed for stable integration of a single HiBiT-GBA1 transgene into an intragenic safe-harbor locus in GBA1-knockout H4 (neuroglioma) cells. This GD cell model was amenable to lead discovery via titration-based quantitative high-throughput screening and lead optimization via structure-activity relationships. A primary screen of 10,779 compounds from the NCATS bioactive collections identified 140 stabilizers of HiBiT-GCase-L444P, including both pharmacological chaperones (ambroxol and noninhibitory chaperone NCGC326) and proteostasis regulators (panobinostat, trans-ISRIB, and pladienolide B). Two complementary high-content imaging-based assays were deployed to triage hits: The fluorescence-quenched substrate LysoFix-GBA captured functional lysosomal GCase activity, while an immunofluorescence assay featuring antibody hGCase-1/23 directly visualized GCase lysosomal translocation. NCGC326 was active in both secondary assays and completely reversed pathological glucosylsphingosine accumulation. Finally, we tested the concept of combination therapy by demonstrating synergistic actions of NCGC326 with proteostasis regulators in enhancing GCase-L444P levels. Looking forward, these physiologically relevant assays can facilitate the identification, pharmacological validation, and medicinal chemistry optimization of small molecules targeting GCase, ultimately leading to a viable therapeutic for GD and PD.

Gaucher disease provides a unique window into Parkinson disease pathogenesis

An exciting development in the field of neurodegeneration is the association between the rare monogenic disorder Gaucher disease and the common complex disorder Parkinson disease (PD). Gaucher disease is a lysosomal storage disorder resulting from an inherited deficiency of the enzyme glucocerebrosidase, encoded by GBA1, which hydrolyses the glycosphingolipids glucosylceramide and glucosylsphingosine. The observation of parkinsonism in a rare subgroup of individuals with Gaucher disease first directed attention to the role of glucocerebrosidase deficiency in the pathogenesis of PD. PD occurs more frequently in people heterozygous for Gaucher GBA1 mutations, and 3-25% of people with Parkinson disease carry a GBA1 variant. However, only a small percentage of individuals with GBA1 variants develop parkinsonism, suggesting that the penetrance is low. Despite over a decade of intense research in this field, including clinical and radiological evaluations, genetic studies and investigations using model systems, the mechanism underlying GBA1-PD is still being pursued. Insights from this association have emphasized the role of lysosomal pathways in parkinsonism. Furthermore, different therapeutic strategies considered or developed for Gaucher disease can now inform drug development for PD.

Fragment-Based Discovery of a Series of Allosteric-Binding Site Modulators of β-Glucocerebrosidase

β-Glucocerebrosidase (GBA/GCase) mutations leading to misfolded protein cause Gaucher's disease and are a major genetic risk factor for Parkinson's disease and dementia with Lewy bodies. The identification of small molecule pharmacological chaperones that can stabilize the misfolded protein and increase delivery of degradation-prone mutant GCase to the lysosome is a strategy under active investigation. Here, we describe the first use of fragment-based drug discovery (FBDD) to identify pharmacological chaperones of GCase. The fragment hits were identified by using X-ray crystallography and biophysical techniques. This work led to the discovery of a series of compounds that bind GCase with nM potency and positively modulate GCase activity in cells.

GBA1-and LRRK2-directed Treatments: The Way Forward

There is an urgent need to identify drug targets for disease modification in Parkinson's Disease (PD). In this mini-review we highlight the reasons genetically-defined drug targets show great promise. Specifically, clinical trials targeting the glucocerebrosidase-1 (GBA1) and leucine-rich repeat kinase 2 (LRRK2) genes are underway. Two key knowledge gaps are 1. How should we modify the GBA1 and LRRK2 pathways? and 2. Which patient populations are most likely to benefit? The exact mechanisms by which mutations in these genes cause PD are not fully understood. Most drugs targeting the GBA1 pathway in clinical trials aim at increasing glucocerebrosidase enzymatic (GCase) activity and targeting the LRRK2 pathway, at reducing its kinase activity. Carriers of mutations in these genes are natural candidates for such interventions; however, there are some biomarker data, specifically for GBA1, to support studying such interventions in non-carriers, i.e., sporadic PD. In summary, we anticipate significant progress in our path towards precision medicine in PD in the coming years.

Development of quantitative high-throughput screening assays to identify, validate, and optimize small-molecule stabilizers of misfolded β-glucocerebrosidase with therapeutic potential for Gaucher disease and Parkinson's disease

Glucocerebrosidase (GCase) is implicated in both a rare, monogenic disorder (Gaucher disease, GD) and a common, multifactorial condition (Parkinson's disease); hence, it is an urgent therapeutic target. To identify correctors of severe protein misfolding and trafficking obstruction manifested by the pathogenic L444P-variant of GCase, we developed a suite of quantitative, high-throughput, cell-based assays. First, we labeled GCase with a small pro-luminescent HiBiT peptide reporter tag, enabling quantitation of protein stabilization in cells while faithfully maintaining target biology. TALEN-based gene editing allowed for stable integration of a single HiBiT-GBA1 transgene into an intragenic safe-harbor locus in GBA1-knockout H4 (neuroglioma) cells. This GD cell model was amenable to lead discovery via titration-based quantitative high-throughput screening and lead optimization via structure-activity relationships. A primary screen of 10,779 compounds from the NCATS bioactive collections identified 140 stabilizers of HiBiT-GCase-L444P, including both pharmacological chaperones (ambroxol and non-inhibitory chaperone NCGC326) and proteostasis regulators (panobinostat, trans-ISRIB, and pladienolide B). Two complementary high-content imaging-based assays were deployed to triage hits: the fluorescence-quenched substrate LysoFix-GBA captured functional lysosomal GCase activity, while an immunofluorescence assay featuring antibody hGCase-1/23 provided direct visualization of GCase lysosomal translocation. NCGC326 was active in both secondary assays and completely reversed pathological glucosylsphingosine accumulation. Finally, we tested the concept of combination therapy, by demonstrating synergistic actions of NCGC326 with proteostasis regulators in enhancing GCase-L444P levels. Looking forward, these physiologically-relevant assays can facilitate the identification, pharmacological validation, and medicinal chemistry optimization of new chemical matter targeting GCase, ultimately leading to a viable therapeutic for two protein-misfolding diseases.

Late-onset Myoclonic Seizure in a 78-year-old Woman with Gaucher Disease

We herein report a 78-year-old woman with Gaucher disease (GD) who was initially diagnosed with GD type 1, had been receiving long-term enzyme replacement therapy since 58 years old, and developed neurological manifestations in her 70s. The neurological manifestations included myoclonic seizures and progressive cognitive decline. Although it is rare for GD patients to first develop neurologic manifestations at such an advanced age, physicians engaged in long-term care for GD patients should be alert for this possibility.

Comparative study of enriched dopaminergic neurons from siblings with Gaucher disease discordant for parkinsonism

Inducible pluripotent stem cells (iPSCs) derived from patient samples have significantly enhanced our ability to model neurological diseases. Comparative studies of dopaminergic (DA) neurons differentiated from iPSCs derived from siblings with Gaucher disease discordant for parkinsonism provides a valuable avenue to explore genetic modifiers contributing to GBA1 -associated parkinsonism in disease-relevant cells. However, such studies are often complicated by the inherent heterogeneity in differentiation efficiency among iPSC lines derived from different individuals. To address this technical challenge, we devised a selection strategy to enrich dopaminergic (DA) neurons expressing tyrosine hydroxylase (TH). A neomycin resistance gene (neo) was inserted at the C-terminus of the TH gene following a T2A self-cleavage peptide, placing its expression under the control of the TH promoter. This allows for TH+ DA neuron enrichment through geneticin selection. This method enabled us to generate comparable, high-purity DA neuron cultures from iPSC lines derived from three sisters that we followed for over a decade: one sibling is a healthy individual, and the other two have Gaucher disease (GD) with GBA1 genotype N370S/c.203delC+R257X (p.N409S/c.203delC+p.R296X). Notably, the younger sister with GD later developed Parkinson disease (PD). A comprehensive analysis of these high-purity DA neurons revealed that although GD DA neurons exhibited decreased levels of glucocerebrosidase (GCase), there was no substantial difference in GCase protein levels or lipid substrate accumulation between DA neurons from the GD and GD/PD sisters, suggesting that the PD discordance is related to of other genetic modifiers.

Secretome Analyses Identify FKBP4 as a GBA1-Associated Protein in CSF and iPS Cells from Parkinson's Disease Patients with GBA1 Mutations

Mutations in the GBA1 gene increase the risk of developing Parkinson's disease (PD). However, most carriers of GBA1 mutations do not develop PD throughout their lives. The mechanisms of how GBA1 mutations contribute to PD pathogenesis remain unclear. Cerebrospinal fluid (CSF) is used for detecting pathological conditions of diseases, providing insights into the molecular mechanisms underlying neurodegenerative disorders. In this study, we utilized the proximity extension assay to examine the levels of metabolism-linked protein in the CSF from 17 PD patients carrying GBA1 mutations (GBA1-PD) and 17 idiopathic PD (iPD). The analysis of CSF secretome in GBA1-PD identified 11 significantly altered proteins, namely FKBP4, THOP1, GLRX, TXNDC5, GAL, SEMA3F, CRKL, APLP1, LRP11, CD164, and NPTXR. To investigate GBA1-associated CSF changes attributed to specific neuronal subtypes responsible for PD, we analyzed the cell culture supernatant from GBA1-PD-induced pluripotent stem cell (iPSC)-derived midbrain dopaminergic (mDA) neurons. The secretome analysis of GBA1-PD iPSC-derived mDA neurons revealed that five differently regulated proteins overlapped with those identified in the CSF analysis: FKBP4, THOP1, GLRX, GAL, and CRKL. Reduced intracellular level of the top hit, FKPB4, was confirmed via Western Blot. In conclusion, our findings identify significantly altered CSF GBA1-PD-associated proteins with FKPB4 being firmly attributed to mDA neurons.

Rapid-Onset Dystonia and Parkinsonism in a Patient With Gaucher Disease

Biallelic mutations in GBA1 cause the lysosomal storage disorder Gaucher disease, and carriers of GBA1 variants have an increased risk of Parkinson's disease (PD). It is still unknown whether GBA1 variants are also associated with other movement disorders. We present the case of a woman with type 1 Gaucher disease who developed acute dystonia and parkinsonism at 35 years of age during a recombinant enzyme infusion treatment. She developed severe dystonia in all extremities and a bilateral pill-rolling tremor that did not respond to levodopa treatment. Despite the abrupt onset of symptoms, neither Sanger nor whole genome sequencing revealed pathogenic variants in ATP1A3 associated with rapid-onset dystonia-parkinsonism (RDP). Further examination showed hyposmia and presynaptic dopaminergic deficits in [18F]-DOPA PET, which are commonly seen in PD but not in RDP. This case extends the spectrum of movement disorders reported in patients with GBA1 mutations, suggesting an intertwined phenotype.

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 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.

Genetic mechanism vs genetic subtypes: The example of GBA

Genetic variants in GBA, encoding the lysosomal enzyme glucocerebrosidase (GCase), are common risk factors for Parkinson's disease (PD). Genotype-phenotype studies have demonstrated that different types of GBA variants have differential effects on the phenotype. Variants could be classified as mild or severe depending on the type of Gaucher disease they cause in the biallelic state. It was shown that severe GBA variants, as compared to mild variants, are associated with higher risk of PD, earlier age at onset, and faster progression of motor and nonmotor symptoms. The observed difference in phenotype might be caused by a diversity of cellular mechanisms related to the particular variants. The lysosomal function of GCase is thought to play a significant role in the development of GBA-associated PD, and other mechanisms such as endoplasmic reticulum retention, mitochondrial dysfunction, and neuroinflammation have also been suggested. Moreover, genetic modifiers such as LRRK2, TMEM175, SNCA, and CTSB can either affect GCase activity or modulate risk and age at onset of GBA-associated PD. To achieve ideal outcomes with precision medicine, therapies will have to be tailored to individuals with specific variants, potentially in combination with known modifiers.

Sex-Specific Microglial Responses to Glucocerebrosidase Inhibition: Relevance to GBA1-Linked Parkinson's Disease

Microglia are heterogenous cells characterized by distinct populations each contributing to specific biological processes in the nervous system, including neuroprotection. To elucidate the impact of sex-specific microglia heterogenicity to the susceptibility of neuronal stress, we video-recorded with time-lapse microscopy the changes in shape and motility occurring in primary cells derived from mice of both sexes in response to pro-inflammatory or neurotoxic stimulations. With this morpho-functional analysis, we documented distinct microglia subpopulations eliciting sex-specific responses to stimulation: male microglia tended to have a more pro-inflammatory phenotype, while female microglia showed increased sensitivity to conduritol-B-epoxide (CBE), a small molecule inhibitor of glucocerebrosidase, the enzyme encoded by the GBA1 gene, mutations of which are the major risk factor for Parkinson's Disease (PD). Interestingly, glucocerebrosidase inhibition particularly impaired the ability of female microglia to enhance the Nrf2-dependent detoxification pathway in neurons, attenuating the sex differences observed in this neuroprotective function. This finding is consistent with the clinical impact of GBA1 mutations, in which the 1.5-2-fold reduced risk of developing idiopathic PD observed in female individuals is lost in the GBA1 carrier population, thus suggesting a sex-specific role for microglia in the etiopathogenesis of PD-GBA1.

Physiologically-Based Pharmacokinetic Model Development, Validation, and Application for Prediction of Eliglustat Drug-Drug Interactions

Eliglustat is a glucosylceramide synthase inhibitor indicated as a long-term substrate reduction therapy for adults with type 1 Gaucher disease, a lysosomal rare disease. It is primarily metabolized by cytochrome P450 2D6 (CYP2D6), and variants in the gene encoding this enzyme are important determinants of eliglustat pharmacokinetics (PK) and drug-drug interactions (DDIs). The existing drug label addresses the DDIs to some extent but has omitted scenarios where both metabolizing CYPs (2D6 and 3A4) are mildly or moderately inhibited. The objectives of this study were (i) to develop and validate an eliglustat physiologically-based pharmacokinetic (PBPK) model with and without drug interactions, (ii) to simulate untested DDI scenarios, and (iii) to explore potential dosing flexibility using lower dose strength of eliglustat (commercially not available). PK data from healthy adults receiving eliglustat with or without interacting drugs were obtained from literature and used for the PBPK model development and validation. The model-predicted single-dose and steady-state maximum concentration (C_max ) and area under the concentration-time curve (AUC) of eliglustat were within 50-150% of the observed values when eliglustat was administered alone or coadministered with ketoconazole or paroxetine. Then as model-based simulations, we illustrated eliglustat exposure as a victim of interaction when coadministered with fluvoxamine following the US Food and Drug Administration (FDA) dosing recommendations. Second, we showed that with lower eliglustat doses (21 mg, 42 mg once daily) the exposure in participants of intermediate and poor metabolizer phenotypes was within the outlined safety margin (C_max <250 ng/mL) when eliglustat was administered with ketoconazole, where the current recommendation is a contraindication of coadministration (84 mg). The present study demonstrated that patients with CYP2D6 deficiency may benefit from lower doses of eliglustat.

Human Induced Pluripotent Stem Cell Phenotyping and Preclinical Modeling of Familial Parkinson's Disease

Parkinson's disease (PD) is primarily idiopathic and a highly heterogenous neurodegenerative disease with patients experiencing a wide array of motor and non-motor symptoms. A major challenge for understanding susceptibility to PD is to determine the genetic and environmental factors that influence the mechanisms underlying the variations in disease-associated traits. The pathological hallmark of PD is the degeneration of dopaminergic neurons in the substantia nigra pars compacta region of the brain and post-mortem Lewy pathology, which leads to the loss of projecting axons innervating the striatum and to impaired motor and cognitive functions. While the cause of PD is still largely unknown, genome-wide association studies provide evidence that numerous polymorphic variants in various genes contribute to sporadic PD, and 10 to 15% of all cases are linked to some form of hereditary mutations, either autosomal dominant or recessive. Among the most common mutations observed in PD patients are in the genes LRRK2, SNCA, GBA1, PINK1, PRKN, and PARK7/DJ-1. In this review, we cover these PD-related mutations, the use of induced pluripotent stem cells as a disease in a dish model, and genetic animal models to better understand the diversity in the pathogenesis and long-term outcomes seen in PD patients.

Rare lysosomal disease registries: lessons learned over three decades of real-world evidence

Lysosomal storage disorders (LSD) are rare diseases, caused by inherited deficiencies of lysosomal enzymes/transporters, that affect 1 in 7000 to 1 in 8000 newborns. Individuals with LSDs face long diagnostic journeys during which debilitating and life-threatening events can occur. Clinical trials and classical descriptions of LSDs typically focus on common manifestations, which are not representative of the vast phenotypic heterogeneity encountered in real-world experience. Additionally, recognizing that there was a limited understanding of the natural history, disease progression, and real-world clinical outcomes of rare LSDs, a collaborative partnership was pioneered 30 years ago to address these gaps. The Rare Disease Registries (RDR) (for Gaucher, Fabry, Mucopolysaccharidosis type I, and Pompe), represent the largest observational database for these LSDs. Over the past thirty years, data from the RDRs have helped to inform scientific understanding and the development of comprehensive monitoring and treatment guidelines by creating a framework for data collection and establishing a standard of care, with an overarching goal to improve the quality of life of affected patients. Here, we highlight the history, process, and impact of the RDRs, and discuss the lessons learned and future directions.

Genetic variations in GBA1 and LRRK2 genes: Biochemical and clinical consequences in Parkinson disease

Variants in the GBA1 and LRRK2 genes are the most common genetic risk factors associated with Parkinson disease (PD). Both genes are associated with lysosomal and autophagic pathways, with the GBA1 gene encoding for the lysosomal enzyme, glucocerebrosidase (GCase) and the LRRK2 gene encoding for the leucine-rich repeat kinase 2 enzyme. GBA1-associated PD is characterized by earlier age at onset and more severe non-motor symptoms compared to sporadic PD. Mutations in the GBA1 gene can be stratified into severe, mild and risk variants depending on the clinical presentation of disease. Both a loss- and gain- of function hypothesis has been proposed for GBA1 variants and the functional consequences associated with each variant is often linked to mutation severity. On the other hand, LRRK2-associated PD is similar to sporadic PD, but with a more benign disease course. Mutations in the LRRK2 gene occur in several structural domains and affect phosphorylation of GTPases. Biochemical studies suggest a possible convergence of GBA1 and LRRK2 pathways, with double mutant carriers showing a milder phenotype compared to GBA1-associated PD. This review compares GBA1 and LRRK2-associated PD, and highlights possible genotype-phenotype associations for GBA1 and LRRK2 separately, based on biochemical consequences of single variants.

Clinical Characteristics, Molecular Background, and Survival of Egyptian Patients With Gaucher Disease Over a 20-Year Follow-up

This study analyzes the general disease characteristics, impact of enzyme replacement therapy (ERT), and overall survival (OS) of 156 Egyptian patients with Gaucher disease (GD) enrolled on hormone replacement from 1998 to 2017. The mean age at diagnosis was 32.46±12.68 months. Anemia was noted at diagnosis in 50%, thrombocytopenia in 30.7%, severe splenomegaly in 58.7%, severe hepatomegaly in 11.9%, and skeletal findings were detected in 24.3% of the patients. The most prevalent GD type was type 3 (54.5%). Twenty-two of type 3 patients had no neurological manifestations at diagnosis, and 12 developed variable central nervous system manifestations during follow-up. The most common neurological features were limited eye movements, oculomotor apraxia, and squint. Of the 60 patients for whom genotypes were obtained, homozygous L444P was the most common (n=35/60, 58.3%). Treatment with ERT (imiglucerase) revealed significant improvements in blood indices, organ volumes, and growth parameters (P<0.05). Ten (11.7%) type 3 patients did not develop any neurological manifestations under ERT over 20 years. Mortality was 16%, and the 20-year OS was 73.3%. We conclude that in Egypt, type 3 is the most prevalent phenotype of GD, and homozygous L444P is the predominant GBA genotype of GD. Early age at diagnosis and treatment with ERT over 20 years revealed significant improvements in disease manifestations, with an OS of 73.3%.

The GBA1 D409V mutation exacerbates synuclein pathology to differing extents in two alpha-synuclein models

Heterozygous mutations in the GBA1 gene - encoding lysosomal glucocerebrosidase (GCase) - are the most common genetic risk factors for Parkinson's disease (PD). Experimental evidence suggests a correlation between decreased GCase activity and accumulation of alpha-synuclein (aSyn). To enable a better understanding of the relationship between aSyn and GCase activity, we developed and characterized two mouse models that investigate aSyn pathology in the context of reduced GCase activity. The first model used constitutive overexpression of wild-type human aSyn in the context of the homozygous GCase activity-reducing D409V mutant form of GBA1. Although increased aSyn pathology and grip strength reductions were observed in this model, the nigrostriatal system remained largely intact. The second model involved injection of aSyn preformed fibrils (PFFs) into the striatum of the homozygous GBA1 D409V knock-in mouse model. The GBA1 D409V mutation did not exacerbate the pathology induced by aSyn PFF injection. This study sheds light on the relationship between aSyn and GCase in mouse models, highlighting the impact of model design on the ability to model a relationship between these proteins in PD-related pathology.

Neuropathological Features of Gaucher Disease and Gaucher Disease with Parkinsonism

Deficient acid β-glucocerebrosidase activity due to biallelic mutations in GBA1 results in Gaucher disease (GD). Patients with this lysosomal storage disorder exhibit a wide range of associated manifestations, spanning from virtually asymptomatic adults to infants with severe neurodegeneration. While type 1 GD (GD1) is considered non-neuronopathic, a small subset of patients develop parkinsonian features. Variants in GBA1 are also an important risk factor for several common Lewy body disorders (LBDs). Neuropathological examinations of patients with GD, including those who developed LBDs, are rare. GD primarily affects macrophages, and perivascular infiltration of Gaucher macrophages is the most common neuropathologic finding. However, the frequency of these clusters and the affected anatomical region varies. GD affects astrocytes, and, in neuronopathic GD, neurons in cerebral cortical layers 3 and 5, layer 4b of the calcarine cortex, and hippocampal regions CA2-4. In addition, several reports describe selective degeneration of the cerebellar dentate nucleus in chronic neuronopathic GD. GD1 is characterized by astrogliosis without prominent neuronal loss. In GD-LBD, widespread Lewy body pathology is seen, often involving hippocampal regions CA2-4. Additional neuropathological examinations in GD are sorely needed to clarify disease-specific patterns and elucidate causative mechanisms relevant to GD, and potentially to more common neurodegenerative diseases.

What have we learned from genome-wide association studies (GWAS) in Parkinson's disease?

After fifteen years of genome-wide association studies (GWAS) in Parkinson's disease (PD), what have we learned? Addressing this question will help catalogue the progress made towards elucidating disease mechanisms, improving the clinical utility of the identified loci, and envisioning how we can harness the strides to develop translational GWAS strategies. Here we review the advances of PD GWAS made to date while critically addressing the challenges and opportunities for next-generation GWAS. Thus, deciphering the missing heritability in underrepresented populations is currently at the reach of hand for a truly comprehensive understanding of the genetics of PD across the different ethnicities. Moreover, state-of-the-art GWAS designs hold a true potential for enhancing the clinical applicability of genetic findings, for instance, by improving disease prediction (PD risk and progression). Lastly, advanced PD GWAS findings, alone or in combination with clinical and environmental parameters, are expected to have the capacity for defining patient enriched cohorts stratified by genetic risk profiles and readily available for neuroprotective clinical trials. Overall, envisioning future strategies for advanced GWAS is currently timely and can be instrumental in providing novel genetic readouts essential for a true clinical translatability of PD genetic findings.

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.

A cross-sectional survey of genetic counselors providing carrier screening regarding GBA variants and Parkinson disease susceptibility

PURPOSE

Adult-onset disease risks associated with carriers of recessive disease have and will continue to be identified. As carrier screening becomes more broadly utilized, providers face the dilemma of whether they should discuss these risks during discussions with prospective parents. This study aimed to understand whether preconception/prenatal genetic counselors (PPGCs) were aware of the risk of Parkinson disease in carriers of, and persons with, Gaucher disease and the reasons behind choosing whether to discuss this risk with patients.

METHODS

Eligible participants included board-certified or board-eligible genetic counselors who had counseled preconception/prenatal patients within the past 3 years. An online survey was distributed via the National Society of Genetic Counselors in November of 2017.

RESULTS

One hundred twenty genetic counselors completed the quantitative survey, distributed in Fall of 2017. While the majority of respondents knew of the Gaucher-related Parkinson's link (n = 78; 65%), just over one-third reported discussing it in preconception/prenatal settings (n = 30; 38.5%). Respondents reported discussing these links more consistently when disclosing positive results or when the patient/family approached the topic. Respondents cited the lack of professional guidelines as one of the main reasons for not discussing the link.

CONCLUSION

These results highlight an inconsistency in PPGCs' discussions of the Parkinson's risk in Gaucher disease carriers, and the need to develop guidelines regarding these issues to help standardize the care and education of patients.

LRRK2, GBA and their interaction in the regulation of autophagy: implications on therapeutics in Parkinson's disease

Mutations in leucine-rich repeat kinase 2 (LRRK2) and glucocerebrosidase (GBA) represent two most common genetic causes of Parkinson’s disease (PD). Both genes are important in the autophagic-lysosomal pathway (ALP), defects of which are associated with α-synuclein (α-syn) accumulation. LRRK2 regulates macroautophagy via activation of the mitogen activated protein kinase/extracellular signal regulated protein kinase (MAPK/ERK) kinase (MEK) and the calcium-dependent adenosine monophosphate (AMP)-activated protein kinase (AMPK) pathways. Phosphorylation of Rab GTPases by LRRK2 regulates lysosomal homeostasis and endosomal trafficking. Mutant LRRK2 impairs chaperone-mediated autophagy, resulting in α-syn binding and oligomerization on lysosomal membranes. Mutations in GBA reduce glucocerebrosidase (GCase) activity, leading to glucosylceramide accumulation, α-syn aggregation and broad autophagic abnormalities. LRRK2 and GBA influence each other: GCase activity is reduced in LRRK2 mutant cells, and LRRK2 kinase inhibition can alter GCase activity in GBA mutant cells. Clinically, LRRK2 G2019S mutation seems to modify the effects of GBA mutation, resulting in milder symptoms than those resulting from GBA mutation alone. However, dual mutation carriers have an increased risk of PD and earlier age of onset compared with single mutation carriers, suggesting an additive deleterious effect on the initiation of PD pathogenic processes. Crosstalk between LRRK2 and GBA in PD exists, but its exact mechanism is unclear. Drugs that inhibit LRRK2 kinase or activate GCase are showing efficacy in pre-clinical models. Since LRRK2 kinase and GCase activities are also altered in idiopathic PD (iPD), it remains to be seen if these drugs will be useful in disease modification of iPD.

Neuroinflammation in aucher disease, neuronal ceroid lipofuscinosis, and commonalities with Parkinson’s disease

Lysosomal storage diseases (LSDs) are rare genetic disorders caused by a disruption in cellular clearance, resulting in pathological storage of undegraded lysosomal substrates. Recent clinical and genetic studies have uncovered links between multiple LSDs and common neurodegenerative diseases such as Parkinson's disease (PD). Here, we review recent literature describing the role of glia cells and neuroinflammation in PD and LSDs, including Gaucher disease (GD) and neuronal ceroid lipofuscinosis (NCL), and highlight converging inflammation pathways that lead to neuron loss. Recent data indicates that lysosomal dysfunction and accumulation of storage materials can initiate the activation of glial cells, through interaction with cell surface or cytosolic pattern recognition receptors that detect pathogenic aggregates of cellular debris. Activated glia cells could act to protect neurons through the elimination of toxic protein or lipid aggregates early in the disease process. However prolonged glial activation that occurs over several decades in chronic-age related neurodegeneration could induce the inappropriate elimination of synapses, leading to neuron loss. These studies provide mechanistic insight into the relationship between lysosomal dysfunction and glial activation, and offer novel therapeutic pathways for the treatment of PD and LSDs focused on reducing neuroinflammation and mitigating cell loss.

Glucocerebrosidase dysfunction in neurodegenerative disease

Parkinson's disease (PD) and related neurodegenerative disorders, termed the synucleinopathies, are characterized pathologically by the accumulation of protein aggregates containing α-synuclein (aSyn), resulting in progressive neuronal loss. There is considerable need for the development of neuroprotective strategies to halt or slow disease progression in these disorders. To this end, evaluation of genetic mutations associated with the synucleinopathies has helped to elucidate crucial mechanisms of disease pathogenesis, revealing key roles for lysosomal and mitochondrial dysfunction. The GBA1 gene, which encodes the lysosomal hydrolase β-glucocerebrosidase (GCase) is the most common genetic risk factor for PD and is also linked to other neurodegenerative disorders including dementia with Lewy bodies (DLB). Additionally, homozygous mutations in GBA1 are associated with the rare lysosomal storage disorder, Gaucher's disease (GD). In this review, we discuss the current knowledge in the field regarding the diverse roles of GCase in neurons and the multifactorial effects of loss of GCase enzymatic activity. Importantly, GCase has been shown to have a bidirectional relationship with aSyn, resulting in a pathogenic feedback loop that can lead to progressive aSyn accumulation. Alterations in GCase activity have furthermore been linked to multiple distinct pathways involved in neurodegeneration, and therefore GCase has emerged as a promising target for therapeutic drug development for PD and related neurodegenerative disorders, particularly DLB.

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.

Counseling for personal health implications identified during reproductive genetic carrier screening

OBJECTIVE

Preconception and prenatal carrier screening is designed to provide reproductive risk information, but carriers for some autosomal recessive or X-linked conditions also have personal health risks. This study investigated the prevalence of and inclusion of personal health implications in pre- and post-test counseling.

METHODS

Twelve genetic conditions with personal health risks for carriers included on carrier screening panels but not otherwise screened routinely were identified (e.g., Gaucher disease with Parkinson's disease risk). A retrospective review was performed of patients with a positive carrier screen for one of these conditions at our center from 2012 to 2019.

RESULTS

Of 6147 individuals that had carrier screening for one of the twelve conditions, 96 (1.56%) did not report a known family history and screened positive for one of the conditions. Testing was ordered largely by reproductive endocrinologists (51.0%) and genetic counselors (35.4%). Most individuals did not receive pre- (96.8%) or post-test (64.6%) counseling about personal health risks. Post-test counseling was performed principally by genetic counselors (97.1%). For carriers of conditions with guidelines for specialist referral, most individuals (75.9%) were referred.

CONCLUSION

Expanded genetic carrier screening increasingly identifies individuals with personal health implications, but patients are frequently not counseled before or after testing. These findings stress the importance of developing guidelines for practitioners about expanded carrier screening counseling and follow-up.

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

Variants in the glucocerebrosidase (GBA) gene are the most common genetic risk factor for Parkinson disease (PD). These include pathogenic variants causing Gaucher disease (GD) (divided into “severe,” “mild,” or “complex”—resulting from recombinant alleles—based on the phenotypic effects in GD) and “risk” variants, which are not associated with GD but nevertheless confer increased risk of PD. As a group, GBA-PD patients have more severe motor and nonmotor symptoms, faster disease progression, and reduced survival compared with noncarriers. However, different GBA variants impact variably on clinical phenotype. In the heterozygous state, “complex” and “severe” variants are associated with a more aggressive and rapidly progressive disease. Conversely, “mild” and “risk” variants portend a more benign course. Homozygous or compound heterozygous carriers usually display severe phenotypes, akin to heterozygous “complex” or “severe” variants carriers. This article reviews genotype–phenotype correlations in GBA-PD, focusing on clinical and nonclinical aspects (neuroimaging and biochemical markers), and explores other disease modifiers that deserve consideration in the characterization of these patients.

Genetic Defects and Pro-inflammatory Cytokines in Parkinson's Disease

Parkinson's disease (PD) is a movement disorder attributed to the loss of dopaminergic (DA) neurons mainly in the substantia nigra pars compacta. Motor symptoms include resting tremor, rigidity, and bradykinesias, while non-motor symptoms include autonomic dysfunction, anxiety, and sleeping problems. Genetic mutations in a number of genes (e.g., LRRK2, GBA, SNCA, PARK2, PARK6, and PARK7) and the resultant abnormal activation of microglial cells are assumed to be the main reasons for the loss of DA neurons in PD with genetic causes. Additionally, immune cell infiltration and their participation in major histocompatibility complex I (MHCI) and/or MHCII-mediated processing and presentation of cytosolic or mitochondrial antigens activate the microglial cells and cause the massive generation of pro-inflammatory cytokines and chemokines, which are all critical for the propagation of brain inflammation and the neurodegeneration in PD with genetic and idiopathic causes. Despite knowing the involvement of several of such immune devices that trigger neuroinflammation and neurodegeneration in PD, the exact disease mechanism or the innovative biomarker that could detect disease severity in PD linked to LRRK2, GBA, SNCA, PARK2, PARK6, and PARK7 defects is largely unknown. The current review has explored data from genetics, immunology, and in vivo and ex vivo functional studies that demonstrate that certain genetic defects might contribute to microglial cell activation and massive generation of a number of pro-inflammatory cytokines and chemokines, which ultimately drive the brain inflammation and lead to neurodegeneration in PD. Understanding the detailed involvement of a variety of immune mediators, their source, and the target could provide a better understanding of the disease process. This information might be helpful in clinical diagnosis, monitoring of disease progression, and early identification of affected individuals.

Neurodegenerative Disease Risk in Carriers of Autosomal Recessive Disease

Genetics has driven significant discoveries in the field of neurodegenerative diseases (NDDs). An emerging theme in neurodegeneration warrants an urgent and comprehensive update: that carrier status of early-onset autosomal recessive (AR) disease, typically considered benign, is associated with an increased risk of a spectrum of late-onset NDDs. Glucosylceramidase beta (GBA1) gene mutations, responsible for the AR lysosomal storage disorder Gaucher disease, are a prominent example of this principle, having been identified as an important genetic risk factor for Parkinson disease. Genetic analyses have revealed further examples, notably GRN, TREM2, EIF2AK3, and several other LSD and mitochondria function genes. In this Review, we discuss the evidence supporting the strikingly distinct allele-dependent clinical phenotypes observed in carriers of such gene mutations and its impact on the wider field of neurodegeneration.

Brain Microglial Activation Increased in Glucocerebrosidase (GBA) Mutation Carriers without Parkinson's disease

BACKGROUND

Glucocerebrosidase gene mutations are a common genetic risk factor for Parkinson's disease. They exhibit incomplete penetrance. The objective of the present study was to measure microglial activation and dopamine integrity in glucocerebrosidase gene mutation carriers without Parkinson's disease compared to controls.

METHODS

We performed PET scans on 9 glucocerebrosidase gene mutation carriers without Parkinson's disease and 29 age-matched controls. We measured microglial activation as 11 C-(R)-PK11195 binding potentials, and dopamine terminal integrity with 18 F-dopa influx constants.

RESULTS

The 11 C-(R)-PK11195 binding potential was increased in the substantia nigra of glucocerebrosidase gene carriers compared with controls (Student t test; right, t = -4.45, P = 0.0001). Statistical parametric mapping also localized significantly increased 11 C-(R)-PK11195 binding potential in the occipital and temporal lobes, cerebellum, hippocampus, and mesencephalon. The degree of hyposmia correlated with nigral 11 C-(R)-PK11195 regional binding potentials (Spearman's rank, P = 0.0066). Mean striatal 18 F-dopa uptake was similar to healthy controls.

CONCLUSIONS

In vivo 11 C-(R)-PK11195 PET imaging detects neuroinflammation in brain regions susceptible to Lewy pathology in glucocerebrosidase gene mutation carriers without Parkinson's. © 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Cross-talks among GBA mutations, glucocerebrosidase, and α-synuclein in GBA-associated Parkinson's disease and their targeted therapeutic approaches: a comprehensive review

Current therapies for Parkinson's disease (PD) are palliative, of which the levodopa/carbidopa therapy remains the primary choice but is unable to modulate the progression of neurodegeneration. Due to the complication of such a multifactorial disorder and significant limitations of the therapy, numerous genetic approaches have been proved effective in finding out genes and mechanisms implicated in this disease. Following the observation of a higher frequency of PD in Gaucher's disease (GD), a lysosomal storage condition, mutations of glycosylceramidase beta (GBA) encoding glucocerebrosidase (GCase) have been shown to be involved and have been explored in the context of PD. GBA mutations are the most common genetic risk factor of PD. Various studies have revealed the relationships between PD and GBA gene mutations, facilitating a better understanding of this disorder. Various hypotheses delineate that the pathological mutations of GBA minimize the enzymatic activity of GCase, which affects the proliferation and clearance of α-synuclein; this affects the lysosomal homeostasis, exacerbating the endoplasmic reticulum stress or encouraging the mitochondrial dysfunction. Identification of the pathological mechanisms underlying the GBA-associated parkinsonism (GBA + PD) advances our understanding of PD. This review based on current literature aims to elucidate various genetic and clinical characteristics correlated with GBA mutations and to identify the numerous pathological processes underlying GBA + PD. We also delineate the therapeutic strategies to interfere with the mutant GCase function for further improvement of the related α-synuclein-GCase crosstalks. Moreover, the various therapeutic approaches such as gene therapy, chaperone proteins, and histone deacetylase inhibitors for the treatment of GBA + PD are discussed.

Cross-talks among GBA mutations, glucocerebrosidase, and α-synuclein in GBA-associated Parkinson’s disease and their targeted therapeutic approaches: a comprehensive review

Current therapies for Parkinson’s disease (PD) are palliative, of which the levodopa/carbidopa therapy remains the primary choice but is unable to modulate the progression of neurodegeneration. Due to the complication of such a multifactorial disorder and significant limitations of the therapy, numerous genetic approaches have been proved effective in finding out genes and mechanisms implicated in this disease. Following the observation of a higher frequency of PD in Gaucher’s disease (GD), a lysosomal storage condition, mutations of glycosylceramidase beta (GBA) encoding glucocerebrosidase (GCase) have been shown to be involved and have been explored in the context of PD. GBA mutations are the most common genetic risk factor of PD. Various studies have revealed the relationships between PD and GBA gene mutations, facilitating a better understanding of this disorder. Various hypotheses delineate that the pathological mutations of GBA minimize the enzymatic activity of GCase, which affects the proliferation and clearance of α-synuclein; this affects the lysosomal homeostasis, exacerbating the endoplasmic reticulum stress or encouraging the mitochondrial dysfunction. Identification of the pathological mechanisms underlying the GBA-associated parkinsonism (GBA + PD) advances our understanding of PD. This review based on current literature aims to elucidate various genetic and clinical characteristics correlated with GBA mutations and to identify the numerous pathological processes underlying GBA + PD. We also delineate the therapeutic strategies to interfere with the mutant GCase function for further improvement of the related α-synuclein–GCase crosstalks. Moreover, the various therapeutic approaches such as gene therapy, chaperone proteins, and histone deacetylase inhibitors for the treatment of GBA + PD are discussed.

Putative second hit rare genetic variants in families with seemingly GBA-associated Parkinson's disease

Rare variants in the beta-glucocerebrosidase gene (GBA1) are common genetic risk factors for alpha synucleinopathy, which often manifests clinically as GBA-associated Parkinson's disease (GBA-PD). Clinically, GBA-PD closely mimics idiopathic PD, but it may present at a younger age and often aggregates in families. Most carriers of GBA variants are, however, asymptomatic. Moreover, symptomatic PD patients without GBA variant have been reported in families with seemingly GBA-PD. These observations obscure the link between GBA variants and PD pathogenesis and point towards a role for unidentified additional genetic and/or environmental risk factors or second hits in GBA-PD. In this study, we explored whether rare genetic variants may be additional risk factors for PD in two families segregating the PD-associated GBA1 variants c.115+1G>A (ClinVar ID: 93445) and p.L444P (ClinVar ID: 4288). Our analysis identified rare genetic variants of the HSP70 co-chaperone DnaJ homolog subfamily B member 6 (DNAJB6) and lysosomal protein prosaposin (PSAP) as additional factors possibly influencing PD risk in the two families. In comparison to the wild-type proteins, variant DNAJB6 and PSAP proteins show altered functions in the context of cellular alpha-synuclein homeostasis when expressed in reporter cells. Furthermore, the segregation pattern of the rare variants in the genes encoding DNAJB6 and PSAP indicated a possible association with PD in the respective families. The occurrence of second hits or additional PD cosegregating rare variants has important implications for genetic counseling in PD families with GBA1 variant carriers and for the selection of PD patients for GBA targeted treatments.

Current Evidence for a Bidirectional Loop Between the Lysosome and Alpha-Synuclein Proteoforms

Cumulative evidence collected in recent decades suggests that lysosomal dysfunction contributes to neurodegenerative diseases, especially if amyloid proteins are involved. Among these, alpha-synuclein (aSyn) that progressively accumulates and aggregates in Lewy bodies is undisputedly a main culprit in Parkinson disease (PD) pathogenesis. Lysosomal dysfunction is evident in brains of PD patients, and mutations in lysosomal enzymes are a major risk factor of PD. At first glance, the role of protein-degrading lysosomes in a disease with pathological protein accumulation seems obvious and should guide the development of straightforward and rational therapeutic targets. However, our review demonstrates that the story is more complicated for aSyn. The protein can possess diverse posttranslational modifications, aggregate formations, and truncations, all of which contribute to a growing known set of proteoforms. These interfere directly or indirectly with lysosome function, reducing their own degradation, and thereby accelerating the protein aggregation and disease process. Conversely, unbalanced lysosomal enzymatic processes can produce truncated aSyn proteoforms that may be more toxic and prone to aggregation. This highlights the possibility of enhancing lysosomal function as a treatment for PD, if it can be confirmed that this approach effectively reduces harmful aSyn proteoforms and does not produce novel, toxic proteoforms.

Diffuse large B-cell non-Hodgkin's lymphoma in Gaucher disease

Gaucher disease type 1 (GD1) is the most common lysosomal storage disease and affects nearly 1 in 40,000 live births. In addition, it is the most common genetic disorder in the Ashkenazi Jewish population with phenotypic variation presenting in early childhood to asymptomatic nonagenarians. There have been a number of studies showing an increased risk of certain malignancies in patients, especially non- Hodgkin's lymphoma (NHL) and multiple myeloma. We describe a 66-year-old Ashkenazi Jewish male with GD1 who was first started on enzyme replacement therapy (ERT) with imiglucerase for GD1 at age 57 years, followed a year later by the diagnosis of diffuse large b-cell non-Hodgkin's lymphoma (DLBCL). He was treated with R-CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone, plus the monoclonal antibody rituximab), however relapsed and developed myelodysplasia necessitating an allo-stem-cell transplantation but succumbed to severe graft vs. host disease. In addition, we also describe a 38-year-old Ashkenazi Jewish male with GD1 who was diagnosed with DLBCL at age 22 years with Gaucher disease diagnosed on pre-treatment bone marrow biopsy which was confirmed by enzyme assay and genotyping. At age 24 years, he was started on ERT with imiglucerase and at age 35 years, he switched to eliglustat. He has remained in remission from the lymphoma. A meta-analysis of the literature will be elaborated upon and we will discuss the relationship of GD1 to NHL and discuss more recent information regarding lyso-GL1 and the development of NHL and multiple myeloma.

A Great Catch for Investigating Inborn Errors of Metabolism-Insights Obtained from Zebrafish

Inborn errors of metabolism cause abnormal synthesis, recycling, or breakdown of amino acids, neurotransmitters, and other various metabolites. This aberrant homeostasis commonly causes the accumulation of toxic compounds or depletion of vital metabolites, which has detrimental consequences for the patients. Efficient and rapid intervention is often key to survival. Therefore, it requires useful animal models to understand the pathomechanisms and identify promising therapeutic drug targets. Zebrafish are an effective tool to investigate developmental mechanisms and understanding the pathophysiology of disorders. In the past decades, zebrafish have proven their efficiency for studying genetic disorders owing to the high degree of conservation between human and zebrafish genes. Subsequently, several rare inherited metabolic disorders have been successfully investigated in zebrafish revealing underlying mechanisms and identifying novel therapeutic targets, including methylmalonic acidemia, Gaucher’s disease, maple urine disorder, hyperammonemia, TRAPPC11-CDGs, and others. This review summarizes the recent impact zebrafish have made in the field of inborn errors of metabolism.

Penetrance of Glucocerebrosidase (GBA) Mutations in Parkinson's Disease: A Kin Cohort Study

BACKGROUND

Homozygous glucocerebrosidase mutations cause Gaucher disease, whereas heterozygous mutations are the most important genetic risk factor for Parkinson's disease (PD). The penetrance of heterozygous glucocerebrosidase mutations for PD is variable (10%-30%), depends on the population studied, and has only been assessed in Gaucher disease or familial PD. The aim of this study was to assess the penetrance of glucocerebrosidase mutations in PD in unselected PD patients.

METHODS

The penetrance of glucocerebrosidase mutations was estimated using the kin-cohort method.

RESULTS

Data on family history were available for 63 of 123 PD glucocerebrosidase mutation carriers, identified among 2843 unrelated consecutive PD patients. Three hundred eighty-one first-degree relatives were analyzed. The risk of developing PD was 10% at 60 years, 16% at 70 years, and 19% at 80 years.

CONCLUSIONS

The estimated penetrance of glucocerebrosidase mutations in unselected PD patients is higher than that estimated in Gaucher disease cohorts and lower than that estimated in familial PD cohorts. © 2020 International Parkinson and Movement Disorder Society.

A Cross-Sectional Retrospective Study of Non-Splenectomized and Never-Treated Patients with Type 1 Gaucher Disease

Patients with type 1 Gaucher disease (GD1) present thrombocytopenia, anemia, organomegaly, and bone complications. Most experts consider that the less aggressive forms do not require specific treatment. However, little is known about the disease course of these forms. The objective of this cross-sectional retrospective study was to compare the clinical, radiological, and laboratory characteristics of patients with less severe GD1 at diagnosis and at the last evaluation to identify features that might lead to potential complications. Non-splenectomized and never-treated patients (19 women and 17 men) were identified in the French Gaucher Disease Registry (FGDR). Their median age was 36.6 years (2.4–75.1), and their median follow-up was 7.8 years (0.4–32.4). Moreover, 38.7% were heterozygous for the GBA1 N370S variant, and 22.6% for the GBA1 L444P variant. From diagnosis to the last evaluation, GD1 did not worsen in 75% of these patients. Some parameters improved (fatigue and hemoglobin concentration), whereas platelet count and chitotriosidase level remained stable. In one patient (2.7%), Lewy body dementia was diagnosed at 46 years of age. Bone lesion onset was late and usually a single event in most patients. This analysis highlights the genotypic heterogeneity of this subgroup, in which disease could remain stable and even improve spontaneously. It also draws attention to the possible risk of Lewy body disease and late onset of bone complications, even if isolated, to be confirmed in larger series and with longer follow-up.

Neurochemical abnormalities in patients with type 1 Gaucher disease on standard of care therapy

Type 1 Gaucher disease (GD1), a glycosphingolipid storage disorder caused by deficient activity of lysosomal glucocerebrosidase, is classically considered non-neuronopathic. However, current evidence challenges this view. Multiple studies show that mutations in GBA1 gene and decreased glucocerebrosidase activity are associated with increased risk for Parkinson disease. We tested the hypothesis that subjects with GD1 will show neurochemical abnormalities consistent with cerebral involvement. We performed Magnetic Resonance Spectroscopy at 7 T to quantify neurochemical profiles in participants with GD1 (n = 12) who are on stable therapy. Age and gender matched healthy participants served as controls (n = 13). Neurochemical profiles were obtained from parietal white matter (PWM), posterior cingulate cortex (PCC), and putamen. Further, in the GD1 group, the neurochemical profiles were compared between individuals with and without a single L444P allele. We observed significantly lower levels of key neuronal markers, N-acetylaspartate, γ-aminobutyric acid, glutamate and glutamate-to-glutamine ratio in PCC of participants with GD1 compared to healthy controls (P < .015). Glutamate concentration was also lower in the putamen in GD1 (P = .01). Glucose + taurine concentration was significantly higher in PWM (P = .04). Interestingly, individuals without L444P had significantly lower aspartate and N-acetylaspartylglutamate in PCC (both P < .001), although this group was 7 years younger than those with an L444P allele. This study demonstrates neurochemical abnormalities in individuals with GD1, for which clinical and prognostic significance remains to be determined. Further studies in a larger cohort are required to confirm an association of neurochemical levels with mutation status and glucocerebrosidase structure and function. SYNOPSIS: Ultrahigh field magnetic resonance spectroscopy reveals abnormalities in neurochemical profiles in patients with GD1 compared to matched healthy controls.

Gut-seeded α-synuclein fibrils promote gut dysfunction and brain pathology specifically in aged mice

Parkinson's disease is a synucleinopathy that is characterized by motor dysfunction, death of midbrain dopaminergic neurons and accumulation of α-synuclein (α-Syn) aggregates. Evidence suggests that α-Syn aggregation can originate in peripheral tissues and progress to the brain via autonomic fibers. We tested this by inoculating the duodenal wall of mice with α-Syn preformed fibrils. Following inoculation, we observed gastrointestinal deficits and physiological changes to the enteric nervous system. Using the AAV-PHP.S capsid to target the lysosomal enzyme glucocerebrosidase for peripheral gene transfer, we found that α-Syn pathology is reduced due to the increased expression of this protein. Lastly, inoculation of α-Syn fibrils in aged mice, but not younger mice, resulted in progression of α-Syn histopathology to the midbrain and subsequent motor defects. Our results characterize peripheral synucleinopathy in prodromal Parkinson's disease and explore cellular mechanisms for the gut-to-brain progression of α-Syn pathology.

Immunoglobulin Abnormalities in Gaucher Disease: an Analysis of 278 Patients Included in the French Gaucher Disease Registry

Gaucher disease (GD) is a rare lysosomal autosomal-recessive disorder due to deficiency of glucocerebrosidase; polyclonal gammopathy (PG) and/or monoclonal gammopathy (MG) can occur in this disease. We aimed to describe these immunoglobulin abnormalities in a large cohort of GD patients and to study the risk factors, clinical significance, and evolution. Data for patients enrolled in the French GD Registry were studied retrospectively. The risk factors of PG and/or MG developing and their association with clinical bone events and severe thrombocytopenia, two markers of GD severity, were assessed with multivariable Cox models and the effect of GD treatment on gammaglobulin levels with linear/logarithmic mixed models. Regression of MG and the occurrence of hematological malignancies were described. The 278 patients included (132 males, 47.5%) were followed up during a mean (SD) of 19 (14) years after GD diagnosis. PG occurred in 112/235 (47.7%) patients at GD diagnosis or during follow-up and MG in 59/187 (31.6%). Multivariable analysis retained age at GD diagnosis as the only independent risk factor for MG (> 30 vs. ≤30 years, HR 4.71, 95%CI [2.40–9.27]; p < 0.001). Risk of bone events or severe thrombocytopenia was not significantly associated with PG or MG. During follow-up, non-Hodgkin lymphoma developed in five patients and multiple myeloma in one. MG was observed in almost one third of patients with GD. Immunoglobulin abnormalities were not associated with the disease severity. However, prolonged surveillance of patients with GD is needed because hematologic malignancies may occur.

GBA1 mutations: Prospects for exosomal biomarkers in α-synuclein pathologies

The discovery that patients with Gaucher Disease (GD), a rare lysosomal storage disorder, were developing symptoms similar to Parkinson's disease (PD) led to investigation of the relationship between the two seemingly unrelated pathologies. GD, an autosomal recessive disorder, is the result of a biallelic mutation in the gene GBA1, which encodes for the enzyme glucocerebrosidase (GCase). Since the observation of its relation to PD, GBA1 mutations have become recognized as the most common genetic risk factor for development of synucleinopathies such as PD and dementia with Lewy bodies. Although the exact mechanism by which GBA1 mutations promote PD is unknown, current understanding suggests that impaired GCase inhibits lysosomal activity and decreases the overall ability of the cell to degrade proteins, specifically the neuronal protein α-synuclein. Decreased elimination of α-synuclein can lead to its abnormal accumulation and aggregation, an important component of PD development. Further understanding of how decreased GCase activity increases risk for α-synuclein pathology can assist with the development of clinical biomarkers for early detection of synucleinopathies, as well as promote novel treatments tailored for people with a GBA1 mutation. Historically, α-synuclein has not been a reliable biomarker for PD. However, recent research on α-synuclein content within exosomes, which are small vesicles released by cells that carry specific cellular cargo, has yielded encouraging results. Moreover, decreased GCase activity has been shown to influence exosomal contents. Exosomes have emerged as a promising new avenue for the identification of novel biomarkers and therapeutic targets aimed at improving neuronal GCase function and limiting the development of synucleinopathies.

Glucocerebrosidase Activity Modulates Neuronal Susceptibility to Pathological α-Synuclein Insult

Mutations in the GBA1 gene are the most common genetic risk factor for Parkinson's disease (PD) and dementia with Lewy bodies (DLB). GBA1 encodes the lysosomal lipid hydrolase glucocerebrosidase (GCase), and its activity has been linked to accumulation of α-synuclein. The current study systematically examines the relationship between GCase activity and both pathogenic and non-pathogenic forms of α-synuclein in primary hippocampal, cortical, and midbrain neuron and astrocyte cultures, as well as in transgenic mice and a non-transgenic mouse model of PD. We find that reduced GCase activity does not result in aggregation of α-synuclein. However, in the context of extant misfolded α-synuclein, GCase activity modulates neuronal susceptibility to pathology. Furthermore, this modulation does not depend on neuron type but rather is driven by the level of pathological α-synuclein seeds. This study has implications for understanding how GBA1 mutations influence PD pathogenesis and provides a platform for testing novel therapeutics.

Approach to Assessment of Parkinson Disease with Emphasis on Genetic Testing

This article presents a nongeneticist's guide to understanding the genetics of Parkinson disease (PD), including clinical diagnostic criteria, differential diagnoses, symptom management, when to suspect a hereditary factor, a summary of autosomal dominant and recessive PD genes, and proposed algorithm for genetic testing. There is increasing availability of genetic testing for PD but there are few recommendations on how these tests should be used in clinical practice. This article guides clinicians on the overall management of patients with PD, with emphasis on determining which patients should have genetic testing and how to interpret the results.