The risk of Parkinson's disease in type 1 Gaucher disease

Modeling bone marrow microenvironment and hematopoietic dysregulation in Gaucher disease through VavCre mediated Gba deletion

Biallelic mutations in Gba cause Gaucher disease (GD), a lysosomal disorder characterized by deficient glucocerebrosidase activity and the accumulation of glucosylceramide (GlcCer) and glucosylsphingosine (GlcSph), primarily in macrophages. Beyond macrophages, GD pathology affects additional hematopoietic lineages, contributing to immune dysregulation. Existing Mx1-Cre Gba knockout models require induction protocols that lead to gene deletion outside hematopoietic cells, limiting the study of hematopoietic-specific effects. To overcome these limitations, we generated a hematopoietic-specific Gba knockout model by crossing Gbafl/fl mice with Vav-Cre, enabling early deletion of Gba exons 8-11 in hematopoietic stem and progenitor cells. These mice were backcrossed to 129X1/SvJ and C57BL/6 J backgrounds, revealing that genetic background significantly influences disease severity. Efficient Gba excision was confirmed in bone marrow, spleen, and thymus, with minimal recombination in the liver. In VavCre 129 GD mice, glucocerebrosidase activity in the spleen was severely reduced, leading to GlcCer and GlcSph accumulation and Gaucher cell infiltration in the spleen and femurs. Transcriptomic analysis identified upregulation of inflammatory and lysosomal pathways. Immune cell deconvolution from RNA-seq data further revealed an expansion of monocytes, dendritic cells, and pro-inflammatory macrophage subsets, suggesting an altered immune landscape. Additionally, GPNMB, a potential GD biomarker, was significantly elevated in both spleens and sera of VavCre 129 GD mice. This hematopoietic-specific GD model provides a powerful platform for studying GD pathophysiology, modifier genes, and immune dysregulation. It offers new opportunities for biomarker discovery and for developing strategies targeting hematopoietic and immune mechanisms in GD and related lysosomal storage disorders.

Classification and Genotype-Phenotype Relationships of GBA1 Variants: MDSGene Systematic Review

Depending on zygosity and the specific change, different variants in the GBA1 gene can cause Parkinson's disease (PD, PARK-GBA1) with reduced penetrance, act as genetic risk factors for PD or parkinsonism, and/or lead to Gaucher's disease (GD). This MDSGene systematic literature review covers 27,963 patients carrying GBA1 variants from 1082 publications with 794 variants, including 13,342 patients with PD or other forms of parkinsonism. It provides a comprehensive overview of demographic, clinical, and genetic findings from an ethnically diverse sample originating from 82 countries across five continents. The most frequent pathogenic or likely pathogenic variants were "N409S" (aka "N370S"; dominating among Jewish and Whites), and "L483P" (aka "L444P"; dominating among Asians and Hispanics), whereas the most common coding risk variants were "E365K" (E326K), and "T408M" (T369M) (both common among Whites). A novel finding is that early-onset PD patients were predominantly of Asian ethnicity, whereas late-onset PD patients were mainly of White ethnicity. Motor cardinal features were similar between PD patients and other forms of parkinsonism, whereas motor complications and non-motor symptoms were more frequently reported in PD patients carrying "severe" variants than in those with "risk" or "mild" variants. Cognitive decline was reported in most patients after surgical treatment, despite achieving a beneficial motor function response. Most GD patients developing PD harbored the "N409S" variant, were of Ashkenazi Jewish ethnicity, and showed a positive response to chronic levodopa treatment. With this review, we start to fill the gaps regarding genotype-phenotype correlations in GBA1 variant carriers, especially concerning PD. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Differential gene expression patterns in Niemann-Pick Type C and Tay-Sachs diseases: Implications for neurodegenerative mechanisms

Lysosomal storage disorders (LSDs) are a group of rare genetic conditions characterized by the impaired function of enzymes responsible for lipid digestion. Among these LSDs, Tay-Sachs disease (TSD) and Niemann-Pick type C (NPC) may share a common gene expression profile. In this study, we conducted a bioinformatics analysis to explore the gene expression profile overlap between TSD and NPC. Analyses were performed on RNA-seq datasets for both TSD and NPC from the Gene Expression Omnibus (GEO) database. Datasets were subjected to differential gene expression analysis utilizing the DESeq2 package in the R programming language. A total of 147 differentially expressed genes (DEG) were found to be shared between the TSD and NPC datasets. Enrichment analysis was then performed on the DEGs. We found that the common DEGs are predominantly associated with processes such as cell adhesion mediated by integrin, cell-substrate adhesion, and urogenital system development. Furthermore, construction of protein-protein interaction (PPI) networks using the Cytoscape software led to the identification of four hub genes: APOE, CD44, SNCA, and ITGB5. Those hub genes not only can unravel the pathogenesis of related neurologic diseases with common impaired pathways, but also may pave the way towards targeted gene therapy of LSDs.In addition, they serve as the potential biomarkers for related neurodegenerative diseases warranting further investigations.

Emerging biomarkers in Gaucher disease

Gaucher disease (GD) is a rare lysosomal disorder characterized by the accumulation of glycosphingolipids in macrophages resulting from glucocerebrosidase (GCase) deficiency. The accumulation of toxic substrates, which causes the hallmark symptoms of GD, is dependent on the extent of enzyme dysfunction. Accordingly, three distinct subtypes have been recognized, with type 1 GD (GD1) as the common and milder form, while types 2 (GD2) and 3 (GD3) are categorized as neuronopathic and severe. Manifestations variably include hepatosplenomegaly, anemia, thrombocytopenia, easy bruising, inflammation, bone pain and other skeletal pathologies, abnormal eye movements and neuropathy. Although the molecular basis of GD is relatively well understood, currently used biomarkers are nonspecific and inadequate for making finer distinctions between subtypes and in evaluating changes in disease status and guiding therapy. Thus, there is continued effort to investigate and identify potential biomarkers to improve GD diagnosis, monitoring and potential identification of novel therapeutic targets. Here, we provide a comprehensive review of emerging biomarkers in GD that can enhance current understanding and improve quality of life through better testing, disease management and treatment.

Synaptic vesicle endocytosis deficits underlie GBA-linked cognitive dysfunction in Parkinson's disease and Dementia with Lewy bodies

GBA is the major risk gene for Parkinson's disease (PD) and Dementia with Lewy Bodies (DLB), two common α-synucleinopathies with cognitive deficits. We investigated the role of mutant GBA in cognitive decline by utilizing Gba (L444P) mutant, SNCA transgenic (tg), and Gba-SNCA double mutant mice. Notably, Gba mutant mice showed early cognitive deficits but lacked PD-like motor deficits or α-synuclein pathology. Conversely, SNCA tg mice displayed age-related motor deficits, without cognitive abnormalities. Gba-SNCA mice exhibited both cognitive decline and exacerbated motor deficits, accompanied by greater cortical phospho-α-synuclein pathology, especially in layer 5 neurons. Single-nucleus RNA sequencing of the cortex uncovered synaptic vesicle (SV) endocytosis defects in excitatory neurons of Gba mutant and Gba-SNCA mice, via robust downregulation of genes regulating SV cycle and synapse assembly. Immunohistochemistry and electron microscopy validated these findings. Our results indicate that Gba mutations, while exacerbating pre-existing α-synuclein aggregation and PD-like motor deficits, contribute to cognitive deficits through α-synuclein-independent mechanisms, involving dysfunction in SV endocytosis.

Unifying biology of neurodegeneration in lysosomal storage diseases

There are currently at least 70 characterised lysosomal storage diseases (LSD) resultant from inherited single-gene defects. Of these, at least 30 present with central nervous system (CNS) neurodegeneration and overlapping aetiology. Substrate accumulation and dysfunctional neuronal lysosomes are common denominator, but how variants in 30 different genes converge on this central cellular phenotype is unclear. Equally unresolved is how the accumulation of a diverse spectrum of substrates in the neuronal lysosomes results in remarkably similar neurodegenerative outcomes. Conversely, how is it that many other monogenic LSDs cause only visceral disease? Lysosomal substance accumulation in LSDs with CNS neurodegeneration (nLSD) includes lipofuscinoses, mucopolysaccharidoses, sphingolipidoses and glycoproteinoses. Here, we review the latest discoveries in the fundamental biology of four classes of nLSDs, comparing and contrasting new insights into disease mechanism with emerging evidence of unifying convergence.

Synaptic vesicle endocytosis deficits underlie GBA-linked cognitive dysfunction in Parkinson's disease and Dementia with Lewy bodies

GBA is the major risk gene for Parkinson's disease (PD) and Dementia with Lewy Bodies (DLB), two common α-synucleinopathies with cognitive deficits. We investigated the role of mutant GBA in cognitive decline by utilizing Gba (L444P) mutant, SNCA transgenic (tg), and Gba-SNCA double mutant mice. Notably, Gba mutant mice showed early cognitive deficits but lacked PD-like motor deficits or α-synuclein pathology. Conversely, SNCA tg mice displayed age-related motor deficits, without cognitive abnormalities. Gba-SNCA mice exhibited both cognitive decline and exacerbated motor deficits, accompanied by greater cortical phospho-α-synuclein pathology, especially in layer 5 neurons. Single-nucleus RNA sequencing of the cortex uncovered synaptic vesicle (SV) endocytosis defects in excitatory neurons of Gba mutant and Gba-SNCA mice, via robust downregulation of genes regulating SV cycle and synapse assembly. Immunohistochemistry and electron microscopy validated these findings. Our results indicate that Gba mutations, while exacerbating pre-existing α-synuclein aggregation and PD-like motor deficits, contribute to cognitive deficits through α-synuclein-independent mechanisms, involving dysfunction in SV endocytosis.

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.

Evaluation of a Liquid Chromatography-Tandem Mass Spectrometry Method for the Analysis of Glucosylceramide and Galactosylceramide Isoforms in Cerebrospinal Fluid of Parkinson's Disease Patients

Mutations in GBA1, encoding glucocerebrosidase beta 1 (GCase), are the most common genetic risk factor for Parkinson's disease (PD). GCase dysfunction leads to an accumulation of glucosylceramide (GluCer) substrates in different organs and fluids. Despite the challenges in quantifying GluCer isoforms in biological samples, their potential clinical interest as PD biomarkers justifies the development of robust assays. An extensively evaluated high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method for quantifying 14 GluCer and galactosylceramide (GalCer) isoforms in human cerebrospinal fluid (CSF) samples is presented. Sample pretreatment, HPLC, and MS/MS parameters were optimized. Evaluation was performed according to the recommendations of the Clinical and Laboratory Standards Institute and European Medicines Agency guidelines. Four 7-point calibration curves were generated, with a linearity interval from 2.5 to 200 nM (R2 ≥ 0.995). The limit of quantification was set at 5 nM. Between-run precision and accuracy were up to 12.5 and 9%, respectively. After method validation, we measured the levels of GluCer and GalCer isoforms in CSF human samples, including 6 healthy controls (HC), 22 idiopathic GBA1 wild-type PD (iPD) patients, and 5 GBA1-associated PD (PD-GBA) patients. GluCer/GalCer median ratios were found to be higher in the CSF of PD-GBA patients, particularly in severe GBA1 mutations, than those in iPD and HC. The observed trends in GluCer/GalCer ratios among groups provide novel information for the comprehensive analysis of sphingolipids as potential biomarkers of PD.

Hematopoietic stem cell transplantation or enzyme replacement therapy in Gaucher disease type 3

Gaucher disease (GD) is a lysosomal storage disorder with glucocerebroside accumulation in the macrophages. The disease is divided into three types based on neurocognitive involvement with GD1 having no involvement while the acute (GD2) and chronic (GD3) are neuronopathic. The non-neurological symptoms of GD3 are well treated with enzyme replacement therapy (ERT) which has replaced hematopoietic stem cell transplantation (HSCT). ERT is unable to prevent neurological progression as the enzyme cannot cross the blood-brain barrier. In this retrospective study, we report the general, neurocognitive, and biochemical outcomes of three siblings with GD3 after treatment with ERT or HSCT. Two were treated with HSCT (named HSCT1 and HSCT2) and one with ERT (ERT1). All patients were homozygous for the c.1448 T > C, (p.Leu483Pro) variant in the GBA1 gene associated with GD3. ERT1 experienced neurocognitive progression with development of seizures, oculomotor apraxia, perceptive hearing loss and mental retardation. HSCT1 had no neurological manifestations, while HSCT2 developed perceptive hearing loss and low IQ. Chitotriosidase concentrations were normal in plasma and cerebrospinal fluid (CSF) for HSCT1 and HSCT2, but both were markedly elevated in ERT1. We report a better neurological outcome and a normalization of chitotriosidase in the two siblings treated with HSCT compared to the ERT-treated sibling. With the advancements in HSCT over the past 25 years, we may reconsider using HSCT in GD3 to achieve a better neurological outcome and limit disease progression.

Activation and Purification of ß-Glucocerebrosidase by Exploiting its Transporter LIMP-2 - Implications for Novel Treatment Strategies in Gaucher's and Parkinson's Disease

Genetic variants of GBA1 can cause the lysosomal storage disorder Gaucher disease and are among the highest genetic risk factors for Parkinson's disease (PD). GBA1 encodes the lysosomal enzyme beta-glucocerebrosidase (GCase), which orchestrates the degradation of glucosylceramide (GluCer) in the lysosome. Recent studies have shown that GluCer accelerates α-synuclein aggregation, exposing GCase deficiency as a major risk factor in PD pathology and as a promising target for treatment. This study investigates the interaction of GCase and three disease-associated variants (p.E326K, p.N370S, p.L444P) with their transporter, the lysosomal integral membrane protein 2 (LIMP-2). Overexpression of LIMP-2 in HEK 293T cells boosts lysosomal abundance of wt, E326K, and N370S GCase and increases/rescues enzymatic activity of the wt and E326K variant. Using a novel purification approach, co-purification of untagged wt, E326K, and N370S GCase in complex with His-tagged LIMP-2 from cell supernatant of HEK 293F cells is achieved, confirming functional binding and trafficking for these variants. Furthermore, a single helix in the LIMP-2 ectodomain is exploited to design a lysosome-targeted peptide that enhances lysosomal GCase activity in PD patient-derived and control fibroblasts. These findings reveal LIMP-2 as an allosteric activator of GCase, suggesting a possible therapeutic potential of targeting this interaction.

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

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

Exploring the efficacy and safety of Ambroxol in Gaucher disease: an overview of clinical studies

Gaucher disease (GD) is mainly caused by glucocerebrosidase (GCase) enzyme deficiency due to genetic variations in the GBA1 gene leading to the toxic accumulation of sphingolipids in various organs, which causes symptoms such as anemia, thrombocytopenia, hepatosplenomegaly, and neurological manifestations. GD is clinically classified into the non-neuronopathic type 1, and the acute and chronic neuronopathic forms, types 2 and 3, respectively. In addition to the current approved GD medications, the repurposing of Ambroxol (ABX) has emerged as a prospective enzyme enhancement therapy option showing its potential to enhance mutated GCase activity and reduce glucosylceramide accumulation in GD-affected tissues of different GBA1 genotypes. The variability in response to ABX varies across different variants, highlighting the diversity in patients' therapeutic outcomes. Its oral availability and safety profile make it an attractive option, particularly for patients with neurological manifestations. Clinical trials are essential to explore further ABX's potential as a therapeutic medication for GD to encourage pharmaceutical companies' investment in its development. This review highlights the potential of ABX as a pharmacological chaperone therapy for GD and stresses the importance of addressing response variability in clinical studies to improve the management of this rare and complex disorder.

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.

Glycolipids in Parkinson's disease: beyond neuronal function

Glycolipid balance is key to normal body function, and its alteration can lead to a variety of diseases involving multiple organs and tissues. Glycolipid disturbances are also involved in Parkinson's disease (PD) pathogenesis and aging. Increasing evidence suggests that glycolipids affect cellular functions beyond the brain, including the peripheral immune system, intestinal barrier, and immunity. Hence, the interplay between aging, genetic predisposition, and environmental exposures could initiate systemic and local glycolipid changes that lead to inflammatory reactions and neuronal dysfunction. In this review, we discuss recent advances in the link between glycolipid metabolism and immune function and how these metabolic changes can exacerbate immunological contributions to neurodegenerative diseases, with a focus on PD. Further understanding of the cellular and molecular mechanisms that control glycolipid pathways and their impact on both peripheral tissues and the brain will help unravel how glycolipids shape immune and nervous system communication and the development of novel drugs to prevent PD and promote healthy aging.

Mechanisms of Glucocerebrosidase Dysfunction in Parkinson's Disease

Beta-glucocerebrosidase is a lysosomal hydrolase, encoded by GBA1 that represents the most common risk gene associated with Parkinson's disease (PD) and Lewy Body Dementia. Glucocerebrosidase dysfunction has been also observed in the absence of GBA1 mutations across different genetic and sporadic forms of PD and related disorders, suggesting a broader role of glucocerebrosidase in neurodegeneration. In this review, we highlight recent advances in mechanistic characterization of glucocerebrosidase function as the foundation for development of novel therapeutics targeting glucocerebrosidase in PD and related disorders.

Surgical treatment of movement disorders in neurometabolic conditions

Refractory movement disorders are a common feature of inborn errors of metabolism (IEMs), significantly impacting quality of life and potentially leading to life-threatening complications such as status dystonicus. Surgical techniques, including deep brain stimulation (DBS) and lesioning techniques, represent an additional treatment option. However, the application and benefits of these procedures in neurometabolic conditions is not well understood. This results in challenges selecting surgical candidates and counseling patients preoperatively. In this review, we explore the literature of surgical techniques for the treatment of movement disorders in IEMs. Globus pallidus internus DBS has emerged as a beneficial treatment option for dystonia in Panthotate-Kinase-associated Neurodegeneration. Additionally, several patients with Lesch-Nyhan Disease have shown improvement following pallidal stimulation, with more robust effects on self-injurious behavior than dystonia. Although there are numerous reports describing benefits of DBS for movement disorders in other IEMs, the sample sizes have generally been small, limiting meaningful conclusions. Currently, DBS is preferred to lesioning techniques. However, successful use of pallidotomy and thalamotomy in neurometabolic conditions has been reported and may have a role in selected patients. Surgical techniques have also been used successfully in patients with IEMs to treat status dystonicus. Advancing our knowledge of these treatment options could significantly improve the care for patients with neurometabolic conditions.

Polygenic Parkinson's Disease Genetic Risk Score as Risk Modifier of Parkinsonism in Gaucher Disease

BACKGROUND

Biallelic pathogenic variants in GBA1 are the cause of Gaucher disease (GD) type 1 (GD1), a lysosomal storage disorder resulting from deficient glucocerebrosidase. Heterozygous GBA1 variants are also a common genetic risk factor for Parkinson's disease (PD). GD manifests with considerable clinical heterogeneity and is also associated with an increased risk for PD.

OBJECTIVE

The objective of this study was to investigate the contribution of PD risk variants to risk for PD in patients with GD1.

METHODS

We studied 225 patients with GD1, including 199 without PD and 26 with PD. All cases were genotyped, and the genetic data were imputed using common pipelines.

RESULTS

On average, patients with GD1 with PD have a significantly higher PD genetic risk score than those without PD (P = 0.021).

CONCLUSIONS

Our results indicate that variants included in the PD genetic risk score were more frequent in patients with GD1 who developed PD, suggesting that common risk variants may affect underlying biological pathways. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Double-Edged Effects of Venglustat on Behavior and Pathology in Mice Overexpressing α-Synuclein

BACKGROUND

Venglustat is a brain-penetrant, small molecule inhibitor of glucosylceramide synthase used in clinical testing for treatment of Parkinson's disease (PD). Despite beneficial effects in certain cellular and rodent models, patients with PD with mutations in GBA, the gene for lysosomal glucocerebrosidase, experienced worsening of their motor function under venglustat treatment (NCT02906020, MOVES-PD, phase 2 trial).

OBJECTIVE

The objective of this study was to evaluate venglustat in mouse models of PD with overexpression of wild-type α-synuclein.

METHODS

Mice overexpressing α-synuclein (Thy1-aSyn line 61) or Gba-mutated mice with viral vector-induced overexpression of α-synuclein in the substantia nigra were administered venglustat as food admixture. Motor and cognitive performance, α-synuclein-related pathology, and microgliosis were compared with untreated controls.

RESULTS

Venglustat worsened motor function in Thy1-aSyn transgenics on the challenging beam and the pole test. Although venglustat did not alter the cognitive deficit in the Y-maze test, it alleviated anxiety-related behavior in the novel object recognition test. Venglustat reduced soluble and membrane-bound α-synuclein in the striatum and phosphorylated α-synuclein in limbic brain regions. Although venglustat reversed the loss of parvalbumin immunoreactivity in the basolateral amygdala, it tended to increase microgliosis and phosphorylated α-synuclein in the substantia nigra. Furthermore, venglustat also partially worsened motor performance and tended to increase neurofilament light chain in the cerebrospinal fluid in the Gba-deficient model with nigral α-synuclein overexpression and neurodegeneration.

CONCLUSIONS

Venglustat treatment in two mouse models of α-synuclein overexpression showed that glucosylceramide synthase inhibition had differential detrimental or beneficial effects on behavior and neuropathology possibly related to brain region-specific effects. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Case report: Multidisciplinary collaboration in diagnosis and treatment of child gaucher disease

Gaucher disease (GD) is an inherited lysosomal storage disease caused by mutations in the glucocerebrosidase gene. The decrease of glucocerebrosidase activity in lysosomes results in the accumulation of its substrate glucocerebroside in the lysosomes of macrophages in organs such as the liver, spleen, bones, lungs, brain and eyes, and the formation of typical storage cells, namely "Gaucher cells", leading to lesions in the affected tissues and organs. Hepatosplenomegaly, bone pain, cytopenia, neurological symptoms, and other systemic manifestations are common in clinical practice. Most pediatric patients have severe symptoms. Early diagnosis and treatment are crucial to improve the curative effect and prognosis. However, due to the low incidence of this disease, multi-system involvement in patients, and diverse clinical manifestations, multidisciplinary teamwork is needed for comprehensive evaluation, diagnosis and treatment. In this study, we reported 2 cases of different types of GD who were diagnosed, treated and followed up by multidisciplinary collaboration in infancy.

Post-translational proteomics platform identifies neurite outgrowth impairments in Parkinson's disease GBA-N370S dopamine neurons

Variants at the GBA locus, encoding glucocerebrosidase, are the strongest common genetic risk factor for Parkinson's disease (PD). To understand GBA-related disease mechanisms, we use a multi-part-enrichment proteomics and post-translational modification (PTM) workflow, identifying large numbers of dysregulated proteins and PTMs in heterozygous GBA-N370S PD patient induced pluripotent stem cell (iPSC) dopamine neurons. Alterations in glycosylation status show disturbances in the autophagy-lysosomal pathway, which concur with upstream perturbations in mammalian target of rapamycin (mTOR) activation in GBA-PD neurons. Several native and modified proteins encoded by PD-associated genes are dysregulated in GBA-PD neurons. Integrated pathway analysis reveals impaired neuritogenesis in GBA-PD neurons and identify tau as a key pathway mediator. Functional assays confirm neurite outgrowth deficits and identify impaired mitochondrial movement in GBA-PD neurons. Furthermore, pharmacological rescue of glucocerebrosidase activity in GBA-PD neurons improves the neurite outgrowth deficit. Overall, this study demonstrates the potential of PTMomics to elucidate neurodegeneration-associated pathways and potential drug targets in complex disease models.

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

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

Sphingolipids in neurodegenerative diseases

Neurodegenerative Diseases (NDDs) are a group of disorders that cause progressive deficits of neuronal function. Recent evidence argues that sphingolipid metabolism is affected in a surprisingly broad set of NDDs. These include some lysosomal storage diseases (LSDs), hereditary sensory and autonomous neuropathy (HSAN), hereditary spastic paraplegia (HSP), infantile neuroaxonal dystrophy (INAD), Friedreich's ataxia (FRDA), as well as some forms of amyotrophic lateral sclerosis (ALS) and Parkinson's disease (PD). Many of these diseases have been modeled in Drosophila melanogaster and are associated with elevated levels of ceramides. Similar changes have also been reported in vertebrate cells and mouse models. Here, we summarize studies using fly models and/or patient samples which demonstrate the nature of the defects in sphingolipid metabolism, the organelles that are implicated, the cell types that are initially affected, and potential therapeutics for these diseases.

[Misdiagnosis of Gaucher disease in real life: Retrospective study of the French Gaucher's disease registry]

INTRODUCTION

Gaucher disease is an autosomal recessive genetic disorder. It is caused by a deficiency of the lysosomal enzyme, glucocerebrosidase which leads to an accumulation of glucosylceramide in the macrophages. Splenomegaly, hepatomegaly, cytopenias (anemia, thrombocytopenia) and bone disorders are the main symptoms. The diagnosis is often delayed, leading to unnecessary investigations and treatments, and delaying the specific treatment. The primary objective of our study was to establish, in patients who had a diagnostic delay of more than one year, the reported misdiagnoses before the final diagnosis. The secondary objectives were to investigate the risk factors associated with error and delayed diagnosis.

METHODS

Retrospective study including patients with Gaucher disease from the French Gaucher Disease Registry. Collection of data by a single investigator from a standardized form.

RESULTS

Among 83 patients with a known diagnostic delay, 13 patients (15 %) had one or two misdiagnoses. These included osteo-articular diagnoses (osteomyelitis, osteoarthritis, arthritis, osteochondritis, rheumatic fever, n=8), haematological diagnoses (gestational thrombocytopenia, immunological thrombocytopenia, n=4), infectious diagnoses (visceral leishmaniasis, mononucleosis, n=2) and hemochromatosis. The osteo-articular and infectious diagnoses concerned the child and the adolescent while the haematological diagnoses and the hemochromatosis concerned the adult. No factors were found associated with misdiagnoses. Patients with a diagnostic delay greater than one year were less likely to have hepatosplenomegaly as the first symptom.

CONCLUSION

There is a risk of diagnostic error related to phenotypic heterogeneity and lack of specificity of Gaucher disease symptoms. This study helps to better identify the misdiagnoses associated with Gaucher disease.

Lipidomics-Paving the Road towards Better Insight and Precision Medicine in Rare Metabolic Diseases

Even though the application of Next-Generation Sequencing (NGS) has significantly facilitated the identification of disease-associated mutations, the diagnostic rate of rare diseases is still below 50%. This causes a diagnostic odyssey and prevents specific treatment, as well as genetic counseling for further family planning. Increasing the diagnostic rate and reducing the time to diagnosis in children with unclear disease are crucial for a better patient outcome and improvement of quality of life. In many cases, NGS reveals variants of unknown significance (VUS) that need further investigations. The delineation of novel (lipid) biomarkers is not only crucial to prove the pathogenicity of VUS, but provides surrogate parameters for the monitoring of disease progression and therapeutic interventions. Lipids are essential organic compounds in living organisms, serving as building blocks for cellular membranes, energy storage and signaling molecules. Among other disorders, an imbalance in lipid homeostasis can lead to chronic inflammation, vascular dysfunction and neurodegenerative diseases. Therefore, analyzing lipids in biological samples provides great insight into the underlying functional role of lipids in healthy and disease statuses. The method of choice for lipid analysis and/or huge assemblies of lipids (=lipidome) is mass spectrometry due to its high sensitivity and specificity. Due to the inherent chemical complexity of the lipidome and the consequent challenges associated with analyzing it, progress in the field of lipidomics has lagged behind other omics disciplines. However, compared to the previous decade, the output of publications on lipidomics has increased more than 17-fold within the last decade and has, therefore, become one of the fastest-growing research fields. Combining multiple omics approaches will provide a unique and efficient tool for determining pathogenicity of VUS at the functional level, and thereby identifying rare, as well as novel, genetic disorders by molecular techniques and biochemical analyses.

A Mouse Model to Test Novel Therapeutics for Parkinson's Disease: an Update on the Thy1-aSyn ("line 61") Mice

Development of neuroprotective therapeutics for Parkinson's disease (PD) is facing a lack of translation from pre-clinical to clinical trials. One strategy for improvement is to increase predictive validity of pre-clinical studies by using extensively characterized animal models with a comprehensive set of validated pharmacodynamic readouts. Mice over-expressing full-length, human, wild-type alpha-synuclein under the Thy-1 promoter (Thy1-aSyn line 61) reproduce key features of sporadic PD, such as progressive loss of striatal dopamine, alpha-synuclein pathology, deficits in motor and non-motor functions, and elevation of inflammatory markers. Extensive work with this model by multiple laboratories over the past decade further increased confidence in its robustness and validity, especially for analyzing pathomechanisms of alpha-synuclein pathology and down-stream pathways, and for pre-clinical drug testing. Interestingly, while postnatal transgene expression is widespread in central and peripheral neurons, the extent and progression of down-stream pathology differs between brain regions, thereby replicating the characteristic selective vulnerability of neurodegenerative diseases. In-depth characterization of these readouts in conjunction with behavioral deficits has led to more informative endpoints for pre-clinical trials. Each drug tested in Thy1-aSyn line 61 enhances knowledge on how molecular targets, pathology, and functional behavioral readouts are interconnected, thereby further optimizing the platform towards predictive validity for clinical trials. Here, we present the current state of the art using Thy1-aSyn line 61 for drug target discovery, validation, and pre-clinical testing.

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.

Neuroinflammation in neuronopathic Gaucher disease: Role of microglia and NK cells, biomarkers, and response to substrate reduction therapy

Background

Neuronopathic Gaucher disease (nGD) is a rare neurodegenerative disorder caused by biallelic mutations in GBA and buildup of glycosphingolipids in lysosomes. Neuronal injury and cell death are prominent pathological features; however, the role of GBA in individual cell types and involvement of microglia, blood-derived macrophages, and immune infiltrates in nGD pathophysiology remains enigmatic.

Methods

Here, using single-cell resolution of mouse nGD brains, lipidomics, and newly generated biomarkers, we found induction of neuroinflammation pathways involving microglia, NK cells, astrocytes, and neurons.

Results

Targeted rescue of Gba in microglia and neurons, respectively, in Gba-deficient, nGD mice reversed the buildup of glucosylceramide (GlcCer) and glucosylsphingosine (GlcSph), concomitant with amelioration of neuroinflammation, reduced serum neurofilament light chain (Nf-L), and improved survival. Serum GlcSph concentration was correlated with serum Nf-L and ApoE in nGD mouse models as well as in GD patients. Gba rescue in microglia/macrophage compartment prolonged survival, which was further enhanced upon treatment with brain-permeant inhibitor of glucosylceramide synthase, effects mediated via improved glycosphingolipid homeostasis, and reversal of neuroinflammation involving activation of microglia, brain macrophages, and NK cells.

Conclusions

Together, our study delineates individual cellular effects of Gba deficiency in nGD brains, highlighting the central role of neuroinflammation driven by microglia activation. Brain-permeant small-molecule inhibitor of glucosylceramide synthase reduced the accumulation of bioactive glycosphingolipids, concomitant with amelioration of neuroinflammation involving microglia, NK cells, astrocytes, and neurons. Our findings advance nGD disease biology whilst identifying compelling biomarkers of nGD to improve patient management, enrich clinical trials, and illuminate therapeutic targets.

Funding

Research grant from Sanofi; other support includes R01NS110354, Yale Liver Center P30DK034989, pilot project grant.

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.

A rare homozygous p.Arg87Trp variant of the GBA gene in Gaucher disease: A case report

Gaucher disease (GD) is a rare metabolic disorder due to pathogenic variants in the GBA gene. We report the first case of the rare p.Arg87Trp pathogenic variant (formerly known as R48W) of the GBA gene in the Tunisian population. A female Arab patient was assessed at the age of 26 due to abdominal distension, bone pain, and headache since she was 25. Physical examination revealed splenomegaly, rib deformation, lumbar scoliosis, and upper limb tremor. Bone marrow was infiltrated by Gaucher cells. The patient was homozygous for the rare p.Arg87Trp variant which is known to be associated with a mild phenotype. This report highlights the necessity of screening the Tunisian population for this rare variant.

Gaucher disease is the most common inherited lysosomal storage disorder. It is a multisystem condition resulting from glucocerebrosidase deficiency, with high inter‐ and intrafamilial phenotypic variability. Gaucher disease patients can be eligible for enzymatic replacement therapy. Therefore, it should be suspected in adults presenting with unexplained splenomegaly and skeletal deformities.

The diagnosis and management of Gaucher disease in pediatric patients: Where do we go from here?

Gaucher disease (GD) is an autosomal recessive inherited lysosomal storage disease that often presents in early childhood and is associated with damage to multiple organ systems. Many challenges associated with GD diagnosis and management arise from the considerable heterogeneity of disease presentations and natural history. Phenotypic classification has traditionally been based on the absence (in type 1 GD) or presence (in types 2 and 3 GD) of neurological involvement of varying severity. However, patient management and prediction of prognosis may be best served by a dynamic, evolving definition of individual phenotype rather than by a rigid system of classification. Patients may experience considerable delays in diagnosis, which can potentially be reduced by effective screening programs; however, program implementation can involve ethical and practical challenges. Variation in the clinical course of GD and an uncertain prognosis also complicate decisions concerning treatment initiation, with differing stakeholder perspectives around efficacy and acceptable cost/benefit ratio. We review the challenges faced by physicians in the diagnosis and management of GD in pediatric patients. We also consider future directions and goals, including acceleration of accurate diagnosis, improvements in the understanding of disease heterogeneity (natural history, response to treatment, and prognosis), the need for new treatments to address unmet needs for all forms of GD, and refinement of the tools for monitoring disease progression and treatment efficacy, such as specific biomarkers.

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.

Development and validation of Gaucher disease type 1 (GD1)-specific patient-reported outcome measures (PROMs) for clinical monitoring and for clinical trials

BACKGROUND

Disease-specific patient-reported outcome measures (PROMs) are fundamental to understanding the impact on, and expectations of, patients with genetic disorders, and can facilitate constructive and educated conversations about treatments and outcomes. However, generic PROMs may fail to capture disease-specific concerns. Here we report the development and validation of a Gaucher disease (GD)-specific PROM for patients with type 1 Gaucher disease (GD1) a lysosomal storage disorder characterized by hepatosplenomegaly, thrombocytopenia, anemia, bruising, bone disease, and fatigue.

RESULTS AND DISCUSSION

The questionnaire was initially developed with input from 85 patients or parents of patients with GD1 or GD3 in Israel. Owing to few participating patients with GD3, content validity was assessed for patients with GD1 only. Content validity of the revised questionnaire was assessed in 33 patients in the US, France, and Israel according to US Food and Drug Administration standards, with input from a panel of six GD experts and one patient advocate representative. Concept elicitation interviews explored patient experience of symptoms and treatments, and a cognitive debriefing exercise explored patients' understanding and relevance of instructions, items, response scales, and recall period. Two versions of the questionnaire were subsequently developed: a 24-item version for routine monitoring in clinical practice (rmGD1-PROM), and a 17-item version for use in clinical trials (ctGD1-PROM). Psychometric validation of the ctGD1-PROM was assessed in 46 adult patients with GD1 and re-administered two weeks later to examine test-retest reliability. Findings from the psychometric validation study revealed excellent internal consistency and strong evidence of convergent validity of the ctGD1-PROM based on correlations with the 36-item Short Form Health Survey. Most items were found to show moderate, good, or excellent test-retest reliability.

CONCLUSIONS

Development of the ctGD1-PROM represents an important step forward for researchers measuring the impact of GD and its respective treatment.

Neurocognitive profile of adults with the Norrbottnian type of Gaucher disease

INTRODUCTION

Gaucher disease (GD) is a monogenic, lysosomal storage disorder, classified according to the presence of acute (type 2), chronic (type 3), or no (type 1) neurological manifestations. The Norrbottnian subtype of neuronopathic GD type 3 (GD3) is relatively frequent in the northern part of Sweden. It exhibits a wide range of neurological symptoms but is characterized by extended life expectancy compared to GD3 in other countries. The aim of our study was to describe the cognitive profile of adult patients with Norrbottnian GD3.

MATERIALS AND METHODS

Ten patients with GD3 (five males and five females) underwent neurocognitive testing with the Repeatable Battery for Assessment of Neuropsychological Status (RBANS). RBANS consists of different short tests that assess Immediate Memory, Visuospatial and Constructional function, Language, Attention, and Delayed Memory. General neurological symptoms of the patients were assessed with the modified severity scoring tool.

RESULTS

Patients (median age 41.5 range 24-57) performed lower than average in all cognitive domains. The overall index score was low (median 58.5, Interquartile range [IQR] 25.5), with the most profound deficit in attention (median 57, IQR 32.5) and immediate memory (median 76.5, IQR 13). Higher scores were found in language (median 83, IQR 21.5), delayed memory (median 81, IQR 41), and visuospatial/constructional function (median 86, IQR 32.35).

CONCLUSION

Norrbottnian GD3 patients showed a unique neurocognitive profile with low overall performance, mostly derived from low scores in attention and memory domains whereas language and visuospatial/constructional ability were relatively spared.

Therapeutics in the Pipeline Targeting α-Synuclein for Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder and the fastest growing neurologic disease in the world, yet no disease-modifying therapy is available for this disabling condition. Multiple lines of evidence implicate the protein α-synuclein (α-Syn) in the pathogenesis of PD, and as such, there is intense interest in targeting α-Syn for potential disease modification. α-Syn is also a key pathogenic protein in other synucleionpathies, most commonly dementia with Lewy bodies. Thus, therapeutics targeting this protein will have utility in these disorders as well. Here we discuss the various approaches that are being investigated to prevent and mitigate α-Syn toxicity in PD, including clearing its pathologic aggregates from the brain using immunization strategies, inhibiting its misfolding and aggregation, reducing its expression level, enhancing cellular clearance mechanisms, preventing its cell-to-cell transmission within the brain and perhaps from the periphery, and targeting other proteins associated with or implicated in PD that contribute to α-Syn toxicity. We also discuss the therapeutics in the pipeline that harness these strategies. Finally, we discuss the challenges and opportunities for the field in the discovery and development of therapeutics for disease modification in PD. SIGNIFICANCE STATEMENT: PD is the second most common neurodegenerative disorder, for which disease-modifying therapies remain a major unmet need. A large body of evidence points to α-synuclein as a key pathogenic protein in this disease as well as in dementia with Lewy bodies, making it of leading therapeutic interest. This review discusses the various approaches being investigated and progress made to date toward discovering and developing therapeutics that would slow and stop progression of these disabling diseases.

Pathological α-syn aggregation is mediated by glycosphingolipid chain length and the physiological state of α-syn in vivo

GBA1 mutations that encode lysosomal β-glucocerebrosidase (GCase) cause the lysosomal storage disorder Gaucher disease (GD) and are strong risk factors for synucleinopathies, including Parkinson's disease and Lewy body dementia. Only a subset of subjects with GBA1 mutations exhibit neurodegeneration, and the factors that influence neurological phenotypes are unknown. We find that α-synuclein (α-syn) neuropathology induced by GCase depletion depends on neuronal maturity, the physiological state of α-syn, and specific accumulation of long-chain glycosphingolipid (GSL) GCase substrates. Reduced GCase activity does not initiate α-syn aggregation in neonatal mice or immature human midbrain cultures; however, adult mice or mature midbrain cultures that express physiological α-syn oligomers are aggregation prone. Accumulation of long-chain GSLs (≥C22), but not short-chain species, induced α-syn pathology and neurological dysfunction. Selective reduction of long-chain GSLs ameliorated α-syn pathology through lysosomal cathepsins. We identify specific requirements that dictate synuclein pathology in GD models, providing possible explanations for the phenotypic variability in subjects with GCase deficiency.

GBA mutations, glucosylceramide and Parkinson's disease

Mutations in GBA, which encodes the lysosomal enzyme glucocerebrosidase, are the highest genetic risk factor for Parkinson's disease (PD), although the mechanistic link between GBA mutations and PD is unknown. An attractive hypothesis is that the lipid substrate of glucocerebrosidase, glucosylceramide, accumulates in patients with PD with a GBA mutation (PD-GBA). Despite the availability of new and accurate methods to quantitatively measure brain glucosylceramide levels, there is little evidence that glucosylceramide, or its deacetylated derivative, glucosylsphingosine, accumulates in human PD or PD-GBA brain or cerebrospinal fluid. Thus, a straightforward association between glucosylceramide levels and the development of PD does not appear valid, necessitating the involvement of other cellular pathways to explain this association, which could involve defects in lysosomal function.

Long-read single molecule real-time (SMRT) sequencing of GBA1 locus in Gaucher disease national cohort from Argentina reveals high frequency of complex allele underlying severe skeletal phenotypes: Collaborative study from the Argentine Group for Diagnosis and Treatment of Gaucher Disease

Gaucher disease is reckoned for extreme phenotypic diversity that does not show consistent genotype/phenotype correlations. In Argentina, a national collaborative group, Grupo Argentino de Diagnóstico y Tratamiento de la Enfermedad de Gaucher, GADTEG, have delineated uniformly severe type 1 Gaucher disease manifestations presenting in childhood with large burden of irreversible skeletal disease. Here using Long-Read Single Molecule Real-Time (SMRT) Sequencing of GBA1 locus, we show that RecNciI allele is highly prevalent and associates with severe skeletal manifestations in childhood.

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.

The remote assessment of parkinsonism supporting ongoing development of interventions in Gaucher disease

Mutations in GBA which are causative of Gaucher disease in their biallelic form, are the most common genetic risk factor for Parkinson's disease (PD). The diagnosis of PD relies upon clinically defined motor features which appear after irreversible neurodegeneration. Prodromal symptoms of PD may provide a means to predict latent pathology, years before the onset of motor features. Previous work has reported prodromal features of PD in GBA mutation carriers, however this has been insufficiently sensitive to identify those that will develop PD. The Remote Assessment of Parkinsonism Supporting Ongoing Development of Interventions in Gaucher Disease (RAPSODI GD) study assesses a large cohort of GBA mutation carriers, to aid development of procedures for earlier diagnosis of PD.

Impact of Gba2 on neuronopathic Gaucher's disease and α-synuclein accumulation in medaka (Oryzias latipes)

Homozygous mutations in the lysosomal glucocerebrosidase gene, GBA1, cause Gaucher’s disease (GD), while heterozygous mutations in GBA1 are a strong risk factor for Parkinson’s disease (PD), whose pathological hallmark is intraneuronal α-synuclein (asyn) aggregates. We previously reported that gba1 knockout (KO) medaka exhibited glucosylceramide accumulation and neuronopathic GD phenotypes, including short lifespan, the dopaminergic and noradrenergic neuronal cell loss, microglial activation, and swimming abnormality, with asyn accumulation in the brains. A recent study reported that deletion of GBA2, non-lysosomal glucocerebrosidase, in a non-neuronopathic GD mouse model rescued its phenotypes. In the present study, we generated gba2 KO medaka and examined the effect of Gba2 deletion on the phenotypes of gba1 KO medaka. The Gba2 deletion in gba1 KO medaka resulted in the exacerbation of glucosylceramide accumulation and no improvement in neuronopathic GD pathological changes, asyn accumulation, or swimming abnormalities. Meanwhile, though gba2 KO medaka did not show any apparent phenotypes, biochemical analysis revealed asyn accumulation in the brains. gba2 KO medaka showed a trend towards an increase in sphingolipids in the brains, which is one of the possible causes of asyn accumulation. In conclusion, this study demonstrated that the deletion of Gba2 does not rescue the pathological changes or behavioral abnormalities of gba1 KO medaka, and GBA2 represents a novel factor affecting asyn accumulation in the brains.

Parkinson's disease and mitophagy: an emerging role for LRRK2

Parkinson's disease (PD) is a progressive neurodegenerative disorder that affects around 2% of individuals over 60 years old. It is characterised by the loss of dopaminergic neurons in the substantia nigra pars compacta of the midbrain, which is thought to account for the major clinical symptoms such as tremor, slowness of movement and muscle stiffness. Its aetiology is poorly understood as the physiological and molecular mechanisms leading to this neuronal loss are currently unclear. However, mitochondrial and lysosomal dysfunction seem to play a central role in this disease. In recent years, defective mitochondrial elimination through autophagy, termed mitophagy, has emerged as a potential contributing factor to disease pathology. PINK1 and Parkin, two proteins mutated in familial PD, were found to eliminate mitochondria under distinct mitochondrial depolarisation-induced stress. However, PINK1 and Parkin are not essential for all types of mitophagy and such pathways occur in most cell types and tissues in vivo, even in the absence of overt mitochondrial stress - so-called basal mitophagy. The most common mutation in PD, that of glycine at position 2019 to serine in the protein kinase LRRK2, results in increased activity and this was recently shown to disrupt basal mitophagy in vivo. Thus, different modalities of mitophagy are affected by distinct proteins implicated in PD, suggesting impaired mitophagy may be a common denominator for the disease. In this short review, we discuss the current knowledge about the link between PD pathogenic mutations and mitophagy, with a particular focus on LRRK2.

Towards physiologically relevant human pluripotent stem cell (hPSC) models of Parkinson's disease

The derivation of human embryonic stem cells followed by the discovery of induced pluripotent stem cells and leaps in genome editing approaches have continuously fueled enthusiasm for the development of new models of neurodegenerative diseases such as Parkinson's disease (PD). PD is characterized by the relative selective loss of dopaminergic neurons (DNs) in specific areas of substantia nigra pars compacta (SNpc). While degeneration in late stages can be widespread, there is stereotypic early degeneration of these uniquely vulnerable neurons. Various causes of selective vulnerability have been investigated but much remains unclear. Most studies have sought to identify cell autonomous properties of the most vulnerable neurons. However, recent findings from genetic studies and model systems have added to our understanding of non-cell autonomous contributions including regional-specific neuro-immune interactions with astrocytes, resident or damage-activated microglia, neuro-glia cell metabolic interactions, involvement of endothelial cells, and damage to the vascular system. All of these contribute to specific vulnerability and, along with aging and environmental factors, might be integrated in a complex stressor-threshold model of neurodegeneration. In this forward-looking review, we synthesize recent advances in the field of PD modeling using human pluripotent stem cells, with an emphasis on organoid and complex co-culture models of the nigrostriatal niche, with emerging CRISPR applications to edit or perturb expression of causal PD genes and associated risk factors, such as GBA, to understand the impact of these genes on relevant phenotypes.

The Cell Biology of LRRK2 in Parkinson's Disease

Point mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of familial Parkinson's disease (PD) and are implicated in a significant proportion of apparently sporadic PD cases. Clinically, LRRK2-driven PD is indistinguishable from sporadic PD, making it an attractive genetic model for the much more common sporadic PD. In this review, we highlight recent advances in understanding LRRK2's subcellular functions using LRRK2-driven PD models, while also considering some of the limitations of these model systems. Recent developments of particular importance include new evidence of key LRRK2 functions in the endolysosomal system and LRRK2's regulation of and by Rab GTPases. Additionally, LRRK2's interaction with the cytoskeleton allowed elucidation of the LRRK2 structure and appears relevant to LRRK2 protein degradation and LRRK2 inhibitor therapies. We further discuss how LRRK2's interactions with other PD-driving genes, such as the VPS35, GBA1, and SNCA genes, may highlight cellular pathways more broadly disrupted in PD.

Therapeutic Potential of αS Evolvability for Neuropathic Gaucher Disease

Gaucher disease (GD), the most common lysosomal storage disorder (LSD), is caused by autosomal recessive mutations of the glucocerebrosidase gene, GBA1. In the majority of cases, GD has a non-neuropathic chronic form with adult onset (GD1), while other cases are more acute and severer neuropathic forms with early onset (GD2/3). Currently, no radical therapies are established for GD2/3. Notably, GD1, but not GD2/3, is associated with increased risk of Parkinson's disease (PD), the elucidation of which might provide a clue for novel therapeutic strategies. In this context, the objective of the present study is to discuss that the evolvability of α-synuclein (αS) might be differentially involved in GD subtypes. Hypothetically, aging-associated PD features with accumulation of αS, and the autophagy-lysosomal dysfunction might be an antagonistic pleiotropy phenomenon derived from αS evolvability in the development in GD1, without which neuropathies like GD2/3 might be manifested due to the autophagy-lysosomal dysfunction. Supposing that the increased severity of GD2/3 might be attributed to the decreased activity of αS evolvability, suppressing the expression of β-synuclein (βS), a potential buffer against αS evolvability, might be therapeutically efficient. Of interest, a similar view might be applicable to Niemann-Pick type C (NPC), another LSD, given that the adult type of NPC, which is comorbid with Alzheimer's disease, exhibits milder medical symptoms compared with those of infantile NPC. Thus, it is predicted that the evolvability of amyloid β and tau, might be beneficial for the adult type of NPC. Collectively, a better understanding of amyloidogenic evolvability in the pathogenesis of LSD may inform rational therapy development.

Cerebrospinal Fluid Profiles in Parkinson's Disease: No Accumulation of Glucosylceramide, but Significant Downregulation of Active Complement C5 Fragment

BACKGROUND

As mutations in glucocerebrosidase 1 (GBA1) are a major risk factor for Parkinson's disease (PD), decreased GBA1 activity might play an important role in the pathogenesis of the disease. However, there are currently no reports on glucosylceramide levels in the cerebrospinal fluid (CSF) in PD.

OBJECTIVE

We investigated whether glucosylceramide accumulation and abnormal immune status in the brain are associated with PD.

METHODS

We measured glucosylceramide by liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) as well as levels of the active fragment of complement C5, C5a, in the CSF of 33 PD, 15 amyotrophic lateral sclerosis (ALS) and 22 neurologically normal control (NNC) subjects. Serum C5a levels in all PD and ALS cases and in a limited number of NNC subjects (n = 8) were also measured.

RESULTS

C5a levels in CSF were significantly downregulated in PD compared with NNC. Moreover, CSF C5a/serum C5a ratio showed pronounced perturbations in PD and ALS patients. LC-ESI-MS/MS revealed a statistically significant accumulation of a specific subspecies of glucosylceramide (d18 : 1/C23 : 0 acyl chain fatty acid) in ALS, but not in PD. Interestingly, CSF glucosylceramide (d18 : 1/C23 : 0) exhibited a significant correlation with CSF C5a levels in PD, but not ALS. No correlation was observed between C5a levels or glucosylceramide subspecies content and disease duration, levodopa equivalent daily dose or Hoehn & Yahr staging in PD.

CONCLUSION

Our findings demonstrate complement dysregulation without glucosylceramide accumulation in PD CSF. Furthermore, we found an association between a specific glucosylceramide subspecies and immune status in PD.

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.