Screening for VPS35 mutations in Parkinson's disease

Identification of high-performing antibodies for Vacuolar protein sorting-associated protein 35 (hVPS35) for use in Western Blot, immunoprecipitation and immunofluorescence

Vacuolar protein sorting-associated protein 35 is a subunit of the retromer complex, a vital constituent of the endosomal protein sorting pathway. The D620N mutation in the VPS35 gene has been reported to be linked to type 17 Parkinson's Disease progression, the exact molecular mechanism remains to be solved. The scientific community would benefit from the accessibility of validated and high-quality anti-hVPS35 antibodies. In this study, we characterized thirteen hVPS35 commercial antibodies for Western Blot, immunoprecipitation, and immunofluorescence using a standardized experimental protocol based on comparing read-outs in knockout cell lines and isogenic parental controls. We identified many high-performing antibodies and encourage readers to use this report as a guide to select the most appropriate antibody for their specific needs.

Endemic parkinsonism: clusters, biology and clinical features

The term 'endemic parkinsonism' refers to diseases that manifest with a dominant parkinsonian syndrome, which can be typical or atypical, and are present only in a particular geographically defined location or population. Ten phenotypes of endemic parkinsonism are currently known: three in the Western Pacific region; two in the Asian-Oceanic region; one in the Caribbean islands of Guadeloupe and Martinique; and four in Europe. Some of these disease entities seem to be disappearing over time and therefore are probably triggered by unique environmental factors. By contrast, other types persist because they are exclusively genetically determined. Given the geographical clustering and potential overlap in biological and clinical features of these exceptionally interesting diseases, this Review provides a historical reference text and offers current perspectives on each of the 10 phenotypes of endemic parkinsonism. Knowledge obtained from the study of these disease entities supports the hypothesis that both genetic and environmental factors contribute to the development of neurodegenerative diseases, not only in endemic parkinsonism but also in general. At the same time, this understanding suggests useful directions for further research in this area.

VPS35 and α-Synuclein fail to interact to modulate neurodegeneration in rodent models of Parkinson's disease

BACKGROUND

Mutations in the vacuolar protein sorting 35 ortholog (VPS35) gene cause late-onset, autosomal dominant Parkinson's disease (PD), with a single missense mutation (Asp620Asn, D620N) known to segregate with disease in families with PD. The VPS35 gene encodes a core component of the retromer complex, involved in the endosomal sorting and recycling of transmembrane cargo proteins. VPS35-linked PD is clinically indistinguishable from sporadic PD, although it is not yet known whether VPS35-PD brains exhibit α-synuclein-positive brainstem Lewy pathology that is characteristic of sporadic cases. Prior studies have suggested a functional interaction between VPS35 and the PD-linked gene product α-synuclein in lower organisms, where VPS35 deletion enhances α-synuclein-induced toxicity. In mice, VPS35 overexpression is reported to rescue hippocampal neuronal loss in human α-synuclein transgenic mice, potentially suggesting a retromer deficiency in these mice.

METHODS

Here, we employ multiple well-established genetic rodent models to explore a functional or pathological interaction between VPS35 and α-synuclein in vivo.

RESULTS

We find that endogenous α-synuclein is dispensable for nigrostriatal pathway dopaminergic neurodegeneration induced by the viral-mediated delivery of human D620N VPS35 in mice, suggesting that α-synuclein does not operate downstream of VPS35. We next evaluated retromer levels in affected brain regions from human A53T-α-synuclein transgenic mice, but find normal levels of the core subunits VPS35, VPS26 or VPS29. We further find that heterozygous VPS35 deletion fails to alter the lethal neurodegenerative phenotype of these A53T-α-synuclein transgenic mice, suggesting the absence of retromer deficiency in this PD model. Finally, we explored the neuroprotective capacity of increasing VPS35 expression in a viral-based human wild-type α-synuclein rat model of PD. However, we find that the overexpression of wild-type VPS35 is not sufficient for protection against α-synuclein-induced nigral dopaminergic neurodegeneration, α-synuclein pathology and reactive gliosis.

CONCLUSION

Collectively, our data suggest a limited interaction of VPS35 and α-synuclein in neurodegenerative models of PD, and do not provide support for their interaction within a common pathophysiological pathway.

A Practical Approach to Early-Onset Parkinsonism

Early-onset parkinsonism (EO parkinsonism), defined as subjects with disease onset before the age of 40 or 50 years, can be the main clinical presentation of a variety of conditions that are important to differentiate. Although rarer than classical late-onset Parkinson’s disease (PD) and not infrequently overlapping with forms of juvenile onset PD, a correct diagnosis of the specific cause of EO parkinsonism is critical for offering appropriate counseling to patients, for family and work planning, and to select the most appropriate symptomatic or etiopathogenic treatments. Clinical features, radiological and laboratory findings are crucial for guiding the differential diagnosis. Here we summarize the most important conditions associated with primary and secondary EO parkinsonism. We also proposed a practical approach based on the current literature and expert opinion to help movement disorders specialists and neurologists navigate this complex and challenging landscape.

Unveiling the cryo-EM structure of retromer

Retromer (VPS26/VPS35/VPS29) is a highly conserved eukaryotic protein complex that localizes to endosomes to sort transmembrane protein cargoes into vesicles and elongated tubules. Retromer mediates retrieval pathways from endosomes to the trans-Golgi network in all eukaryotes and further facilitates recycling pathways to the plasma membrane in metazoans. In cells, retromer engages multiple partners to orchestrate the formation of tubulovesicular structures, including sorting nexin (SNX) proteins, cargo adaptors, GTPases, regulators, and actin remodeling proteins. Retromer-mediated pathways are especially important for sorting cargoes required for neuronal maintenance, which links retromer loss or mutations to multiple human brain diseases and disorders. Structural and biochemical studies have long contributed to the understanding of retromer biology, but recent advances in cryo-electron microscopy and cryo-electron tomography have further uncovered exciting new snapshots of reconstituted retromer structures. These new structures reveal retromer assembles into an arch-shaped scaffold and suggest the scaffold may be flexible and adaptable in cells. Interactions with cargo adaptors, particularly SNXs, likely orient the scaffold with respect to phosphatidylinositol-3-phosphate (PtdIns3P)-enriched membranes. Pharmacological small molecule chaperones have further been shown to stabilize retromer in cultured cell and mouse models, but mechanisms by which these molecules bind remain unknown. This review will emphasize recent structural and biophysical advances in understanding retromer structure as the field moves towards a molecular view of retromer assembly and regulation on membranes.

Clinical manifestations of Parkinson's disease harboring VPS35 retromer complex component p.D620N with long-term follow-up

INTRODUCTION

To identify and investigate patients with Parkinson's disease (PD) harboring VPS35 variants in Japan.

METHODS

Using targeted gene panel screening, we analyzed 393 familial, 294 young-onset, and 52 late-onset sporadic PD patients derived from the Juntendo PD DNA bank, and obtained clinical information from the medical records on each patient in whom we found VPS35 p.D620N variants.

RESULTS

We identified VPS35 p.D620N in three new patients: two patients with familial PD and one patient with sporadic PD. Additionally, we newly confirmed p.D620 from a patient of a family reported previously. The prevalence of familial PD was 0.7% (2/307), young-onset sporadic PD was 0.3% (1/294), and late-onset sporadic PD was 0% (0/52) in our cohort. Combining four patients with p.D620N from our previous reports, haplotype analysis indicated at least two founders in our cohort. Patients commonly showed a slow progression of parkinsonism with onset in middle or late age and mild parkinsonism with good response to levodopa and little cognitive decline even for more than 10 years of disease duration. Psychosis was occurred in two patients. One-half of patients required device-aided therapies such as deep brain stimulation or levodopa-carbidopa intestinal gel. Brain magnetic resonance imaging mostly showed normal findings, even at more than 10 years after onset. ¹²³I-metaiodobenzylguanidine myocardial scintigraphy indicated normal heart-to-mediastinum ratio values among three of four patients.

CONCLUSIONS

Patients with VPS35 p.D620N showed distinctive symptoms and neuroimaging. Our findings expand the clinical findings of patients with VPS35 variants.

Formation of retromer transport carriers is disrupted by the Parkinson disease-linked Vps35 D620N variant

Retromer core complex is an endosomal scaffold that plays a critical role in orchestrating protein trafficking within the endosomal system. Here we characterized the effect of the Parkinson's disease-linked Vps35 D620N in the endo-lysosomal system using Vps35 D620N rescue cell models. Vps35 D620N fully rescues the lysosomal and autophagy defects caused by retromer knock-out. Analogous to Vps35 knock out cells, the endosome-to-trans-Golgi network transport of cation-independent mannose 6-phosphate receptor (CI-M6PR) is impaired in Vps35 D620N rescue cells because of a reduced capacity to form endosome transport carriers. Cells expressing the Vps35 D620N variant have altered endosomal morphology, resulting in smaller, rounder structures with less tubule-like branches. At the molecular level retromer incorporating Vps35 D620N variant has a decreased binding to retromer associated proteins wiskott-aldrich syndrome protein and SCAR homologue (WASH) and SNX3 which are known to associate with retromer to form the endosome transport carriers. Hence, the partial defects on retrograde protein trafficking carriers in the presence of Vps35 D620N represents an altered cellular state able to cause Parkinson's disease.

Olfactory Dysfunction in Familial and Sporadic Parkinson's Disease

This minireview discusses our current understanding of the olfactory dysfunction that is frequently observed in sporadic and familial forms of Parkinson's disease and parkinsonian syndromes. We review the salient characteristics of olfactory dysfunction in these conditions, discussing its prevalence and characteristics, how neuronal processes and circuits are altered in Parkinson's disease, and what is assessed by clinically used measures of olfactory function. We highlight how studies of monogenic Parkinson's disease and investigations in ethnically diverse populations have contributed to understanding the mechanisms underlying olfactory dysfunction. Furthermore, we discuss how imaging and system-level approaches have been used to understand the pathogenesis of olfactory dysfunction. We discuss the challenging, remaining gaps in understanding the basis of olfactory dysfunction in neurodegeneration. We propose that insights could be obtained by following longitudinal cohorts with familial forms of Parkinson's disease using a combination of approaches: a multifaceted longitudinal assessment of olfactory function during disease progression is essential to identify not only how dysfunction arises, but also to address its relationship to motor and non-motor Parkinson's disease symptoms. An assessment of cohorts having monogenic forms of Parkinson's disease, available within the Genetic Epidemiology of Parkinson's Disease (GEoPD), as well as other international consortia, will have heuristic value in addressing the complexity of olfactory dysfunction in the context of the neurodegenerative process. This will inform our understanding of Parkinson's disease as a multisystem disorder and facilitate the more effective use of olfactory dysfunction assessment in identifying prodromal Parkinson's disease and understanding disease progression.

Long-Term Outcomes of Genetic Parkinson's Disease

Parkinson’s disease (PD) is a progressive neurodegenerative disorder that affects 1–2% of people by the age of 70 years. Age is the most important risk factor, and most cases are sporadic without any known environmental or genetic causes. Since the late 1990s, mutations in the genes SNCA, PRKN, LRRK2, PINK1, DJ-1, VPS35, and GBA have been shown to be important risk factors for PD. In addition, common variants with small effect sizes are now recognized to modulate the risk for PD. Most studies in genetic PD have focused on finding new genes, but few have studied the long-term outcome of patients with the specific genetic PD forms. Patients with known genetic PD have now been followed for more than 20 years, and we see that they may have distinct and different prognoses. New therapeutic possibilities are emerging based on the genetic cause underlying the disease. Future medication may be based on the pathophysiology individualized to the patient’s genetic background. The challenge is to find the biological consequences of different genetic variants. In this review, the clinical patterns and long-term prognoses of the most common genetic PD variants are presented.

Genetic predispositions of Parkinson's disease revealed in patient-derived brain cells

Parkinson's disease (PD) is the second most prevalent neurological disorder and has been the focus of intense investigations to understand its etiology and progression, but it still lacks a cure. Modeling diseases of the central nervous system in vitro with human induced pluripotent stem cells (hiPSC) is still in its infancy but has the potential to expedite the discovery and validation of new treatments. Here, we discuss the interplay between genetic predispositions and midbrain neuronal impairments in people living with PD. We first summarize the prevalence of causal Parkinson's genes and risk factors reported in 74 epidemiological and genomic studies. We then present a meta-analysis of 385 hiPSC-derived neuronal lines from 67 recent independent original research articles, which point towards specific impairments in neurons from Parkinson's patients, within the context of genetic predispositions. Despite the heterogeneous nature of the disease, current iPSC models reveal converging molecular pathways underlying neurodegeneration in a range of familial and sporadic forms of Parkinson's disease. Altogether, consolidating our understanding of robust cellular phenotypes across genetic cohorts of Parkinson's patients may guide future personalized drug screens in preclinical research.

The Role of VPS35 in the Pathobiology of Parkinson's Disease

The vacuolar protein sorting 35 (VPS35) gene located on chromosome 16 has recently emerged as a cause of late-onset familial Parkinson's disease (PD) (PARK17). The gene encodes a 796-residue protein nearly ubiquitously expressed in human tissues. The protein localizes on endosomes where it assembles with other peripheral membrane proteins to form the retromer complex. How VPS35 mutations induce dopaminergic neuron degeneration in humans is still unclear. Because the retromer complex recycles the receptors that mediate the transport of hydrolase to lysosome, it has been suggested that VPS35 mutations lead to impaired lysosomal and autophagy function. Recent studies also demonstrated that VPS35 and the retromer complex influence mitochondrial homeostasis, suggesting that VPS35 mutations elicit mitochondrial dysfunction. More recent studies have identified a key role of VPS35 in neurotransmission, whilst others reported a functional interaction between VPS35 and other genes associated with familial PD, including α-SYNUCLEIN-PARKIN-LRRK2. Here, we review the biological role of VPS35 protein, the VPS35 mutations identified in human PD patients, and the potential molecular mechanism by which VPS35 mutations can induce progressive neurodegeneration in PD.

VPS35-Based Approach: A Potential Innovative Treatment in Parkinson's Disease

Several symptomatic treatments for Parkinson's disease (PD) are currently available. Still, the challenge today is to find a therapy that might reduce degeneration and slow down disease progression. The identification of pathogenic mutations in familial Parkinsonism (fPD) associated to the monogenic forms of PD provided pathophysiological insights and highlighted novel targets for therapeutic intervention. Mutations in the VPS35 gene have been associated with autosomal dominant fPD and a clinical phenotype indistinguishable from idiopathic PD. Although VPS35 mutations are relatively rare causes of PD, their study may help understanding specific cellular and molecular alterations that lead to accumulation α-synuclein in neurons of PD patients. Interacting with such mechanisms may provide innovative therapeutic approaches. We review here the evidence on the physiological role of VPS35 as a key intracellular trafficking protein controlling relevant neuronal functions. We further analyze VPS35 activity on α-synuclein degradation pathways that control the equilibrium between α-synuclein clearance and accumulation. Finally, we highlight the strategies for increasing VPS35 levels as a potential tool to treat PD.

Deep brain stimulation and genetic variability in Parkinson's disease: a review of the literature

Deep brain stimulation is offered as symptomatic treatment in advanced Parkinson's disease, depending on a clinical assessment of the individual patient's risk-benefit profile. Genetics contribute to phenotypic variability in Parkinson's disease, suggesting that genetic testing could have clinical relevance for personalized therapy. Aiming to review current evidence linking genetic variation to deep brain stimulation treatment and outcomes in Parkinson's disease we performed systematic searches in the Embase and PubMed databases to identify relevant publications and summarized the findings. We identified 39 publications of interest. Genetic screening studies indicate that monogenic forms of Parkinson's disease and high-risk variants of GBA may be more common in cohorts treated with deep brain stimulation. Studies assessing deep brain stimulation outcomes in patients carrying mutations in specific genes are limited in size. There are reports suggesting that the phenotype associated with parkin mutations could be suitable for early surgery. In patients with LRRK2 mutations, outcomes of deep brain stimulation seem at least as good as in mutation-negative patients, whereas less favorable outcomes are seen in patients carrying mutations in GBA. Careful assessment of clinical symptoms remains the primary basis for clinical decisions associated with deep brain stimulation surgery in Parkinson's disease, although genetic information could arguably be taken into account in special cases. Current evidence is scarce, but highlights a promising development where genetic profiling may be increasingly relevant for clinicians tailoring personalized medical or surgical therapy to Parkinson's disease patients.

Deep brain stimulation and genetic variability in Parkinson's disease: a review of the literature

Deep brain stimulation is offered as symptomatic treatment in advanced Parkinson’s disease, depending on a clinical assessment of the individual patient’s risk-benefit profile. Genetics contribute to phenotypic variability in Parkinson’s disease, suggesting that genetic testing could have clinical relevance for personalized therapy. Aiming to review current evidence linking genetic variation to deep brain stimulation treatment and outcomes in Parkinson’s disease we performed systematic searches in the Embase and PubMed databases to identify relevant publications and summarized the findings. We identified 39 publications of interest. Genetic screening studies indicate that monogenic forms of Parkinson’s disease and high-risk variants of GBA may be more common in cohorts treated with deep brain stimulation. Studies assessing deep brain stimulation outcomes in patients carrying mutations in specific genes are limited in size. There are reports suggesting that the phenotype associated with parkin mutations could be suitable for early surgery. In patients with LRRK2 mutations, outcomes of deep brain stimulation seem at least as good as in mutation-negative patients, whereas less favorable outcomes are seen in patients carrying mutations in GBA. Careful assessment of clinical symptoms remains the primary basis for clinical decisions associated with deep brain stimulation surgery in Parkinson’s disease, although genetic information could arguably be taken into account in special cases. Current evidence is scarce, but highlights a promising development where genetic profiling may be increasingly relevant for clinicians tailoring personalized medical or surgical therapy to Parkinson’s disease patients.

Contributions of VPS35 Mutations to Parkinson's Disease

Parkinson's Disease (PD) is a multi-system neurodegenerative disease where approximately 90% of cases are idiopathic. The remaining 10% of the cases can be traced to a genetic origin and research has largely focused on these associated genes to gain a better understanding of the molecular and cellular pathogenesis for PD. The gene encoding vacuolar protein sorting protein 35 (VPS35) has been definitively linked to late onset familial PD following the identification of a point mutation (D620N) as the causal agent in a Swiss family. Since its discovery, numerous studies have been undertaken to characterize the role of VPS35 in cellular processes and efforts have been directed toward understanding the perturbations caused by the D620N mutation. In this review, we examine what is currently known about VPS35, which has pleiotropic effects, as well as proposed mechanisms of pathogenesis by the D620N mutation. A brief survey of other VPS35 polymorphisms is also provided. Lastly, model systems that are being utilized for these investigations and possible directions for future research are discussed.

Deep brain stimulation for monogenic Parkinson's disease: a systematic review

Deep brain stimulation (DBS) is an effective treatment for Parkinson’s disease (PD) patients with motor fluctuations and dyskinesias. The key DBS efficacy studies were performed in PD patients with unknown genotypes; however, given the estimated monogenic mutation prevalence of approximately 5–10%, most commonly LRRK2, PRKN, PINK1 and SNCA, and risk-increasing genetic factors such as GBA, proper characterization is becoming increasingly relevant. We performed a systematic review of 46 studies that reported DBS effects in 221 genetic PD patients. The results suggest that monogenic PD patients have variable DBS benefit depending on the mutated gene. Outcome appears excellent in patients with the most common LRRK2 mutation, p.G2019S, and good in patients with PRKN mutations but poor in patients with the more rare LRRK2 p.R1441G mutation. The overall benefit of DBS in SNCA, GBA and LRRK2 p.T2031S mutations may be compromised due to rapid progression of cognitive and neuropsychiatric symptoms. In the presence of other mutations, the motor changes in DBS-treated monogenic PD patients appear comparable to those of the general PD population.

The genetic landscape of Parkinson's disease

The cause of Parkinson's disease (PD) remains unknown in most patients. Since 1997, with the first genetic mutation known to cause PD described in SNCA gene, many other genes with Mendelian inheritance have been identified. We summarize genetic, clinical and neuropathological findings related to the 27 genes reported in the literature since 1997, associated either with autosomal dominant (AD): LRRK2, SNCA, VPS35, GCH1, ATXN2, DNAJC13, TMEM230, GIGYF2, HTRA2, RIC3, EIF4G1, UCHL1, CHCHD2, and GBA; or autosomal recessive (AR) inheritance: PRKN, PINK1, DJ1, ATP13A2, PLA2G6, FBXO7, DNAJC6, SYNJ1, SPG11, VPS13C, PODXL, and PTRHD1; or an X-linked transmission: RAB39B. Clinical and neuropathological variability among genes is great. LRRK2 mutation carriers present a phenotype similar to those with idiopathic PD whereas, depending on the SNCA mutations, the phenotype ranges from early onset typical PD to dementia with Lewy bodies, including many other atypical forms. DNAJC6 nonsense mutations lead to a very severe phenotype whereas DNAJC6 missense mutations cause a more typical form. PRKN, PINK1 and DJ1 cases present with typical early onset PD with slow progression, whereas other AR genes present severe atypical Parkinsonism. RAB39B is responsible for a typical phenotype in women and a variable phenotype in men. GBA is a major PD risk factor often associated with dementia. A growing number of reported genes described as causal genes (DNAJC13, TMEM230, GIGYF2, HTRA2, RIC3, EIF4G1, UCHL1, and CHCHD2) are still awaiting replication or indeed have not been replicated, thus raising questions as to their pathogenicity. Phenotypic data collection and next generation sequencing of large numbers of cases and controls are needed to differentiate pathogenic dominant mutations with incomplete penetrance from rare, non-pathogenic variants. Although known genes cause a minority of PD cases, their identification will lead to a better understanding their pathological mechanisms, and may contribute to patient care, genetic counselling, prognosis determination and finding new therapeutic targets.

The Golgi-localized, gamma ear-containing, ARF-binding (GGA) protein family alters alpha synuclein (α-syn) oligomerization and secretion

Several age-related neurodegenerative disorders are associated with protein misfolding and aggregation of toxic peptides. α-synuclein (α-syn) aggregation and the resulting cytotoxicity is a hallmark of Parkinson's disease (PD) as well as dementia with Lewy bodies. Rising evidence points to oligomeric and pre-fibrillar forms as the pathogenic species, and oligomer secretion seems to be crucial for the spreading and progression of PD pathology. Recent studies implicate that dysfunctions in endolysosomal/autophagosomal pathways increase α-syn secretion. Mutation in the retromer-complex protein VPS35, which is involved in endosome to Golgi transport, was suggested to cause familial PD. GGA proteins regulate vesicular traffic between Golgi and endosomes and might work as antagonists for retromer complex mediated transport. To investigate the role of the GGAs in the α-syn oligomerization and/or secretion process we utilized protein-fragment complementation assays (PCA). We here demonstrate that GGAs alter α-syn oligomer secretion and α-syn oligomer-mediated toxicity. Specifically, we determined that GGA3 modifies extracellular α-syn species in an exosome-independent manner. Our data suggest that GGA3 drives α-syn oligomerization in endosomal compartments and thus facilitates α-syn oligomer secretion. Preventing the early events in α-syn oligomer release may be a novel approach to halt disease spreading in PD and other synucleinopathies.

Retromer Dysfunction and Neurodegenerative Disease

In recent years, genomic, animal and cell biology studies have implicated deficiencies in retromer-mediated trafficking of proteins in an increasing number of neurodegenerative diseases including Alzheimer's Disease (AD), Parkinson's Disease (PD) and Frontotemporal Lobar Degener-ation (FTLD). The retromer complex, which is highly conserved across all eukaryotes, regulates the sorting of transmembrane proteins out of endo-somes to the cell surface or to the trans-Golgi network. Within retromer, cargo selection and binding are performed by a trimer of the Vps26, Vps29 and Vps35 proteins, named the "Cargo-Selective Complex (CSC)". Sorting of cargo into tubules for distribution to the trans-Golgi network or the cell sur-face is achieved through the dimeric sorting nexin (SNX) component of retromer and accessory proteins such as the WASH complex which medi-ates the formation of discrete endosomal tubules enabling the sorting of cargo into distinct pathways through production of filamentous actin patch-es. In the present article, we review the molecular structure and function of the retromer and summarize the evidence linking retromer dysfunction to neurodegenerative disease.

VPS35, the Retromer Complex and Parkinson's Disease

Mutations in the vacuolar protein sorting 35 ortholog (VPS35) gene encoding a core component of the retromer complex, have recently emerged as a new cause of late-onset, autosomal dominant familial Parkinson’s disease (PD). A single missense mutation, AspD620Asn (D620N), has so far been unambiguously identified to cause PD in multiple individuals and families worldwide. The exact molecular mechanism(s) by which VPS35 mutations induce progressive neurodegeneration in PD are not yet known. Understanding these mechanisms, as well as the perturbed cellular pathways downstream of mutant VPS35, is important for the development of appropriate therapeutic strategies. In this review, we focus on the current knowledge surrounding VPS35 and its role in PD. We provide a critical discussion of the emerging data regarding the mechanisms underlying mutant VPS35-mediated neurodegeneration gleaned from genetic cell and animal models and highlight recent advances that may provide insight into the interplay between VPS35 and several other PD-linked gene products (i.e. α-synuclein, LRRK2 and parkin) in PD. Present data support a role for perturbed VPS35 and retromer function in the pathogenesis of PD.

Identification of VPS35 p.D620N mutation-related Parkinson's disease in a Taiwanese family with successful bilateral subthalamic nucleus deep brain stimulation: a case report and literature review

Background

Vacuolar protein sorting 35 (VPS35) was recently reported to be a genetic cause for late-onset autosomal dominant Parkinson’s disease (PD). However, VPS35 mutations are rarely reported in Asian populations. Herein, we report the first Taiwanese family with the pathogenic VPS35 p.D620N mutation, including one patient treated successfully with subthalamic nucleus deep brain stimulation (STN-DBS).

Case presentation

A 61-year-old woman presented with progressive left hand resting tremor at the age of 42. Neurological examinations revealed mask face and akinetic-rigidity over left extremities. She showed a good response to levodopa treatment, and her unified Parkinson’s disease rating scale (UPDRS) motor scores improved from 42 to 15 under the levodopa equivalent dose of 1435 mg/day. She developed peak-dose dyskinesia and motor fluctuation seven years after the onset of symptoms, and received bilateral STN-DBS at the age of 55. Stimulation led to a marked improvement in her motor symptoms with a 37% improvement in the UPDRS motor score during the OFF period five years after surgery. The patient’s mother and three siblings were also diagnosed with PD in their forties, following an autosomal-dominant inheritance pattern. We performed genetic analysis of the proband using a targeted next generation sequencing (NGS) panel covering 17 known PD-causative genes. We identified a pathogenic missense mutation in VPS35 gene, c.1858G > A (p.D620N), in this patient.

Conclusions

This is the first report of the VPS35 p.D620N mutation in a Taiwanese family. Additionally, our report contributes to the current understanding of genetically defined PD patients treated successfully with STN-DBS.

An updated review of Parkinson's disease genetics and clinicopathological correlations

Knowledge regarding the pathophysiological basis of Parkinson's disease (PD) has been greatly expanded over the past two decades, with extraordinary contributions from the field of genetics. However, genetic classifications became complex, difficult to follow, and at times misleading, by placing well-established monogenic forms of the disease along with others associated with risk loci, often ill characterized. The present paper summarizes the genetic, clinical, and neuropathological findings of the currently described monogenic forms of PD and also approaches the progress made in determining genetic risk factors for PD. Furthermore, the text incorporates the data into a recently proposed classification system that will hopefully bring a "user-friendly" approach to this issue. This paper also highlights a number of inconsistencies regarding classification of PD as a single, unique clinicopathological entity-in fact, in order to achieve the development of truly innovative therapies, PD should probably be regarded clinically as a "Parkinson's disease cluster", instead of a single disease. In the future, we hope that an in-depth and groundbreaking understanding of PD will allow the development of truly disease-modifying therapies that will target the molecular processes responsible for the cascade of pathological events underlying each form of PD.

Vacuolar Protein Sorting Genes in Parkinson's Disease: A Re-appraisal of Mutations Detection Rate and Neurobiology of Disease

Mammalian retromers play a critical role in protein trans-membrane sorting from endosome to the trans-Golgi network (TGN). Recently, retromer alterations have been related to the onset of Parkinson's Disease (PD) since the variant p.Asp620Asn in VPS35 (Vacuolar Protein Sorting 35) was identified as a cause of late onset PD. This variant causes a primary defect in endosomal trafficking and retromers formation. Other mutations in VPS genes have been reported in both sporadic and familial PD. These mutations are less defined. Understanding the specific prevalence of all VPS gene mutations is key to understand the relevance of retromers impairment in the onset of PD. A number of PD-related mutations despite affecting different biochemical systems (autophagy, mitophagy, proteasome, endosomes, protein folding), all converge in producing an impairment in cell clearance. This may explain how genetic predispositions to PD may derive from slightly deleterious VPS mutations when combined with environmental agents overwhelming the clearance of the cell. This manuscript reviews genetic data produced in the last 5 years to re-define the actual prevalence of VPS gene mutations in the onset of PD. The prevalence of p.Asp620Asn mutation in VPS35 is 0.286 of familial PD. This increases up to 0.548 when considering mutations affecting all VPS genes. This configures mutations in VPS genes as the second most frequent autosomal dominant PD genotype. This high prevalence, joined with increased awareness of the role played by retromers in the neurobiology of PD, suggests environmentally-induced VPS alterations as crucial in the genesis of PD.

Genetic perspective on the role of the autophagy-lysosome pathway in Parkinson disease

Parkinson disease (PD), once considered as a prototype of a sporadic disease, is now known to be considerably affected by various genetic factors, which interact with environmental factors and the normal process of aging, leading to PD. Large studies determined that the hereditary component of PD is at least 27%, and in some populations, single genetic factors are responsible for more than 33% of PD patients. Interestingly, many of these genetic factors, such as LRRK2, GBA, SMPD1, SNCA, PARK2, PINK1, PARK7, SCARB2, and others, are involved in the autophagy-lysosome pathway (ALP). Some of these genes encode lysosomal enzymes, whereas others correspond to proteins that are involved in transport to the lysosome, mitophagy, or other autophagic-related functions. Is it possible that all these factors converge into a single pathway that causes PD? In this review, we will discuss these genetic findings and the role of the ALP in the pathogenesis of PD and will try to answer this question. We will suggest a novel hypothesis for the pathogenic mechanism of PD that involves the lysosome and the different autophagy pathways.

The role of the retromer complex in aging-related neurodegeneration: a molecular and genomic review

The retromer coat complex is a vital component of the intracellular trafficking mechanism sorting cargo from the endosomes to the trans-Golgi network or to the cell surface. In recent years, genes encoding components of the retromer coat complex and members of the vacuolar protein sorting 10 (Vps10) family of receptors, which play pleiotropic functions in protein trafficking and intracellular/intercellular signaling in neuronal and non-neuronal cells and are primary cargos of the retromer complex, have been implicated as genetic risk factors for sporadic and autosomal dominant forms of several neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease and frontotemporal lobar degeneration. In addition to their functions in protein trafficking, the members of the Vps10 receptor family (sortilin, SorL1, SorCS1, SorCS2, and SorCS3) modulate neurotrophic signaling pathways. Both sortilin and SorCS2 act as cell surface receptors to mediate acute responses to proneurotrophins. In addition, sortilin can modulate the intracellular response to brain-derived neurotrophic factor (BDNF) by direct control of BDNF levels and regulating anterograde trafficking of Trk receptors to the synapse. This review article summarizes the emerging data from this rapidly growing field of intracellular trafficking signaling in the pathogenesis of neurodegeneration.

In vivo evidence of pathogenicity of VPS35 mutations in the Drosophila

Mutations of VPS35, a component of the retromer complex have been associated with late onset familial Parkinson's disease. The D620N mutation in VPS35 appears to be most prevalent, however, P316S was found in two cases within the same family and a control, whereas L774M was identified in 6 cases and 1 control. In vivo evidence of their pathogenicity is lacking. Here we investigated the in vivo effects of P316S, D620N and L774M using Drosophila as a model. We generated transgenic human VPS35-expressing mutations and demonstrated that VPS35 D620N transgenic flies led to late-onset loss of TH-positive DA neurons, poor mobility, shortened lifespans and increased sensitivity to rotenone, a PD-linked environmental toxin, with some of these phenotypes observed for P316S but not in L774M transgenic flies. We conclude that D620N and to a smaller extent P316S are associated with pathogenicity in PD.

Recent advances in Parkinson’s disease genetics

The last 5 years have seen rapid progress in Parkinson’s disease (PD) genetics, with the publication of a series of large-scale genome wide association studies for PD, and evaluation of the roles of the LRRK2 and GBA genes in the aetiology of PD. We are beginning to develop a coherent picture of the interplay of Mendelian and non-Mendelian factors in PD. Pathways involved in mitochondrial quality control (mitophagy), lysosomal function and immune function are emerging as important in the pathogenesis of PD. These pathways represent a target for therapeutic intervention and a way in which the heterogeneity of disease cause, as well as disease mechanism, can be established. In the future, there is likely to be an individualised basis for the treatment of PD, linked to the identification of specific genetic factors.

Parkinson's disease-linked mutations in VPS35 induce dopaminergic neurodegeneration

Mutations in the vacuolar protein sorting 35 homolog (VPS35) gene at the PARK17 locus, encoding a key component of the retromer complex, were recently identified as a new cause of late-onset, autosomal dominant Parkinson's disease (PD). Here we explore the pathogenic consequences of PD-associated mutations in VPS35 using a number of model systems. VPS35 exhibits a broad neuronal distribution throughout the rodent brain, including within the nigrostriatal dopaminergic pathway. In the human brain, VPS35 protein levels and distribution are similar in tissues from control and PD subjects, and VPS35 is not associated with Lewy body pathology. The common D620N missense mutation in VPS35 does not compromise its protein stability or localization to endosomal and lysosomal vesicles, or the vesicular sorting of the retromer cargo, sortilin, SorLA and cation-independent mannose 6-phosphate receptor, in rodent primary neurons or patient-derived human fibroblasts. In yeast we show that PD-linked VPS35 mutations are functional and can normally complement VPS35 null phenotypes suggesting that they do not result in a loss-of-function. In rat primary cortical cultures the overexpression of human VPS35 induces neuronal cell death and increases neuronal vulnerability to PD-relevant cellular stress. In a novel viral-mediated gene transfer rat model, the expression of D620N VPS35 induces the marked degeneration of substantia nigra dopaminergic neurons and axonal pathology, a cardinal pathological hallmark of PD. Collectively, these studies establish that dominant VPS35 mutations lead to neurodegeneration in PD consistent with a gain-of-function mechanism, and support a key role for VPS35 in the development of PD.

Advances in the Genetics of Parkinson's Disease: A Guide for the Clinician

Over the last 16 years, insights in clinical and genetic characteristics of Parkinson's disease (PD) have increased substantially. We summarize the clinical, genetic, and pathological findings of autosomal dominant PD linked to mutations in SNCA, leucine-rich repeat kinase 2, vacuolar protein sorting-35, and eukaryotic translation initiation factor 4 gamma 1 and autosomal recessive PD linked to parkin,PINK1, and DJ-1, as well as autosomal recessive complicated parkinsonian syndromes caused by mutations in ATP13A2,FBXO7,PLA2G6,SYNJ1, and DNAJC6. We also review the advances in high- and low-risk genetic susceptibility factors and present multisystem disorders that may present with parkinsonism as the major clinical feature and provide recommendations for prioritization of genetic testing. Finally, we consider the challenges of future genetic research in PD.

VPS35 Parkinson's disease phenotype resembles the sporadic disease

Recently a new autosomal dominant Parkinson's disease mutation (p.Asp620Asn) in the VPS35 gene was discovered. The clinical features of 14 PD patients with this mutation from three Austrian families were evaluated. Age at disease-onset appears lower and depression was more common in Austrian patients compared to sporadic PD patients. However, we were unable to identify a specific clinical maker of VPS35 patients, who otherwise resemble sporadic PD patients.

The pallidopyramidal syndromes: nosology, aetiology and pathogenesis

Purpose of review

The aims of this review is to suggest a new nomenclature and classification system for the diseases currently categorized as neurodegeneration with brain iron accumulation (NBIA) or dystonia-parkinsonism, and to discuss the mechanisms implicated in the pathogenesis of these diseases.

Recent findings

NBIA is a disease category encompassing syndromes with iron accumulation and prominent dystonia–parkinsonism. However, as there are many diseases with similar clinical presentations but without iron accumulation and/or known genetic cause, the current classification system and nomenclature remain confusing. The pathogenetic mechanisms of these diseases and the causes of gross iron accumulation and significant burden of neuroaxonal spheroids are also elusive. Recent genetic and functional studies have identified surprising links between NBIA, Parkinson's disease and lysosomal storage disorders (LSD) with the common theme being a combined lysosomal–mitochondrial dysfunction. We hypothesize that mitochondria and lysosomes form a functional continuum with a predominance of mitochondrial and lysosomal pathways in NBIA and LSD, respectively, and with Parkinson's disease representing an intermediate form of disease.

Summary

During the past 18 months, important advances have been made towards understanding the genetic and pathological underpinnings of the pallidopyramidal syndromes with important implications for clinical practice and future treatment developments.

Advances in the genetics of Parkinson disease

Parkinson disease (PD) is a multifactorial neurodegenerative disease that was long considered the result of environmental factors. In the past 15 years, however, a genetic aetiology for PD has begun to emerge. Here, we review results from linkage and next-generation sequencing studies of familial parkinsonism, as well as candidate gene and genome-wide association findings in sporadic PD. In these studies, many of the genetic findings overlap, despite different designs and study populations, highlighting novel therapeutic targets. The molecular results delineate a sequence of pathological events whereby deficits in synaptic exocytosis and endocytosis, endosomal trafficking, lysosome-mediated autophagy and mitochondrial maintenance increase susceptibility to PD. These discoveries provide the rationale, molecular insight and research tools to develop neuroprotective and disease-modifying therapies.

VPS35 and EIF4G1 mutations are rare in Parkinson's disease among Indians

Mutations in 2 genes, vacuolar protein sorting homolog 35 (VPS35) and eukaryotic translation initiation factor 4 gamma 1 (EIF4G1), have been recently reported as causal in autosomal dominant Parkinson's disease (PD) among Caucasians. Their contribution to PD in other ethnic groups remains limited with 1% of VPS35 mutations observed in Caucasian and Japanese populations, but none in Chinese, and 11.57% of EIF4G1 mutations in Caucasian families and 0.09% and 0.17% in Caucasian and Chinese sporadic cases, respectively. We investigated the contribution, if any, of these 2 genes to familial and sporadic PD among the ethnically distinct Indian population. Complete exonic regions of these 2 genes were resequenced in 15 well-characterized PD families; the reported p.Asp620Asn in VPS35 and p.Arg1205His in EIF4G1 mutations were screened in an additional 54 familial and 251 sporadic PD cases, and no mutations were observed. These results, together with our previous reports on the absence of mutations in SNCA and LRRK2, warrant a continuing search for novel causative genes for PD among Indians.

A multi-centre clinico-genetic analysis of the VPS35 gene in Parkinson disease indicates reduced penetrance for disease-associated variants

Background

Two recent studies identified a mutation (p.Asp620Asn) in the vacuolar protein sorting 35 gene as a cause for an autosomal dominant form of Parkinson disease . Although additional missense variants were described, their pathogenic role yet remains inconclusive.

Methods and results

We performed the largest multi-center study to ascertain the frequency and pathogenicity of the reported vacuolar protein sorting 35 gene variants in more than 15,000 individuals worldwide. p.Asp620Asn was detected in 5 familial and 2 sporadic PD cases and not in healthy controls, p.Leu774Met in 6 cases and 1 control, p.Gly51Ser in 3 cases and 2 controls. Overall analyses did not reveal any significant increased risk for p.Leu774Met and p.Gly51Ser in our cohort.

Conclusions

Our study apart from identifying the p.Asp620Asn variant in familial cases also identified it in idiopathic Parkinson disease cases, and thus provides genetic evidence for a role of p.Asp620Asn in Parkinson disease in different populations worldwide.

The VPS35 gene and Parkinson's disease

Parkinson's disease (PD), the second most common age-related neurodegenerative disease, is characterized by loss of dopaminergic and nondopaminergic neurons, leading to a variety of motor and nonmotor symptoms. In addition to environmental factors, genetic predisposition and specific gene mutations have been shown to play an important role in the pathogenesis of this disorder. Recently, the identification of the vacuolar protein sorting 35 homolog gene (VPS35), linked to autosomal dominant late-onset PD, has provided new clues to the pathogenesis of PD. Here we discuss the VPS35 gene, its protein function, and various pathways involved in Wnt/β-catenin signaling and in the role of DMT1 mediating the uptake of iron and iron translocation from endosomes to the cytoplasm. Further understanding of these mechanisms will undoubtedly provide new insights into the pathogenic mechanisms of PD and may lead to prevention and better treatment of the disorder.

Monogenic Parkinson's disease and parkinsonism: clinical phenotypes and frequencies of known mutations

Mutations in seven genes are robustly associated with autosomal dominant (SNCA, LRRK2, EIF4G1, VPS35) or recessive (parkin/PARK2, PINK1, DJ1/PARK7) Parkinson's disease (PD) or parkinsonism. Changes in a long list of additional genes have been suggested as causes for parkinsonism or PD, including genes for hereditary ataxias (ATXN2, ATXN3, FMR1), frontotemporal dementia (C9ORF72, GRN, MAPT, TARDBP), DYT5 (GCH1, TH, SPR), and others (ATP13A2, CSF1R, DNAJC6, FBXO, GIGYF2, HTRA2, PLA2G6, POLG, SPG11, UCHL1). This review summarizes the clinical features of diseases caused by mutations in these genes, and their frequencies. Point mutations and multiplications in SNCA cause cognitive or psychiatric symptoms, parkinsonism, dysautonomia and myoclonus with widespread alpha-synuclein pathology in the central and peripheral nervous system. LRRK2 mutations may lead to a clinical phenotype closely resembling idiopathic PD with a puzzling variety in neuropathology. Mutations in parkin/PARK2, PINK1 or DJ1/PARK7 may cause early-onset parkinsonism with a low risk for cognitive decline and a pathological process usually restricted to the brainstem. Carriers of mutations in the other genes may develop parkinsonism with or without additional symptoms, but rarely a disease resembling PD. The pathogenicity of several mutations remains unconfirmed. Although some mutations occur with high frequency in specific populations, worldwide all are very rare. The genetic cause of the majority of patients with sporadic or hereditary PD remains unknown in most populations. Clinical genetic testing is useful for selected patients. Testing strategies need to be adapted individually based on clinical phenotype and estimated frequency of the mutation in the patient's population.

Whole exome sequencing of rare variants in EIF4G1 and VPS35 in Parkinson disease

OBJECTIVE

Recently, vacuolar protein sorting 35 (VPS35) and eukaryotic translation initiation factor 4 gamma 1 (EIF4G1) have been identified as 2 causal Parkinson disease (PD) genes. We used whole exome sequencing for rapid, parallel analysis of variations in these 2 genes.

METHODS

We performed whole exome sequencing in 213 patients with PD and 272 control individuals. Those rare variants (RVs) with <5% frequency in the exome variant server database and our own control data were considered for analysis. We performed joint gene-based tests for association using RVASSOC and SKAT (Sequence Kernel Association Test) as well as single-variant test statistics.

RESULTS

We identified 3 novel VPS35 variations that changed the coded amino acid (nonsynonymous) in 3 cases. Two variations were in multiplex families and neither segregated with PD. In EIF4G1, we identified 11 (9 nonsynonymous and 2 small indels) RVs including the reported pathogenic mutation p.R1205H, which segregated in all affected members of a large family, but also in 1 unaffected 86-year-old family member. Two additional RVs were found in isolated patients only. Whereas initial association studies suggested an association (p = 0.04) with all RVs in EIF4G1, subsequent testing in a second dataset for the driving variant (p.F1461) suggested no association between RVs in the gene and PD.

CONCLUSIONS

We confirm that the specific EIF4G1 variation p.R1205H seems to be a strong PD risk factor, but is nonpenetrant in at least one 86-year-old. A few other select RVs in both genes could not be ruled out as causal. However, there was no evidence for an overall contribution of genetic variability in VPS35 or EIF4G1 to PD development in our dataset.

VPS35 Asp620Asn and EIF4G1 Arg1205His mutations are rare in Parkinson disease from southwest China

The Asp620Asn mutation in the vacuolar protein sorting protein 35 (VPS35) gene and the Arg1205His mutation in the eukaryotic translation initiation factor 4 gamma 1 (EIF4G1) gene were identified in autosomal dominant late-onset familial and sporadic Parkinson disease (PD) patients in a Caucasian population. However, the frequencies of these 2 mutations among Chinese PD patients are unknown. We examined these mutations in a large cohort consisting of 609 PD patients and 600 healthy control subjects from Southwest China. Our results suggest that the Asp620Asn mutation in VPS35 and the Arg1205His mutation in EIF4G1 do not play a role in PD in the Southwest China population. The novel Arg1205Cys mutation in EIF4G1 detected in the current study should be further studied among other Asian patients.

Genetics of Parkinson disease and other movement disorders

PURPOSE OF REVIEW

We will review the recent advances in the genetics of Parkinson disease and other movement disorders such as dystonia, essential tremor and restless legs syndrome (RLS).

RECENT FINDINGS

Mutations in VPS35 were identified as a novel cause of autosomal dominant Parkinson disease using exome sequencing. Next generation sequencing (NGS) was also used to identify PRRT2 mutations as a cause of paroxysmal kinesigenic dyskinesia (DYT10). Using a different technique, that is linkage analysis, mutations in EIF4G1 were implicated as a cause of Parkinson disease and mutations in SLC20A2 as a cause of familial idiopathic basal ganglia calcification. Furthermore, genome-wide association studies (GWAS) and meta-analyses have confirmed known risk genes and identified new risk loci in Parkinson disease, RLS and essential tremor. New models to study genetic forms of Parkinson disease, such as stem cell-derived neurons, have helped to elucidate disease-relevant molecular pathways, such as the molecular link between Gaucher disease and Parkinson disease.

SUMMARY

New genes have been implicated in Parkinson disease and other movement disorders through the use of NGS. The identification of risk variants has been facilitated by GWAS and meta-analyses. Furthermore, new models are being developed to study the molecular mechanisms involved in the pathogenesis of these diseases.

Suppression of dynamin GTPase decreases α-synuclein uptake by neuronal and oligodendroglial cells: a potent therapeutic target for synucleinopathy

Background

The intracellular deposition of misfolded proteins is a common neuropathological hallmark of most neurodegenerative disorders. Increasing evidence suggests that these pathogenic proteins may spread to neighboring cells and induce the propagation of neurodegeneration.

Results

In this study, we have demonstrated that α-synuclein (αSYN), a major constituent of intracellular inclusions in synucleinopathies, was taken up by neuronal and oligodendroglial cells in both a time- and concentration-dependent manner. Once incorporated, the extracellular αSYN was immediately assembled into high-molecular-weight oligomers and subsequently formed cytoplasmic inclusion bodies. Furthermore, αSYN uptake by neurons and cells of the oligodendroglial lineage was markedly decreased by the genetic suppression and pharmacological inhibition of the dynamin GTPases, suggesting the involvement of the endocytic pathway in this process.

Conclusions

Our findings shed light on the mode of αSYN uptake by neuronal and oligodendroglial cells and identify therapeutic strategies aimed at reducing the propagation of protein misfolding.

The use of next-generation sequencing in movement disorders

New advances in genomic technology are being introduced at a greater speed and are revolutionizing the field of genetics for both complex and Mendelian diseases. For instance, during the past few years, genome-wide association studies (GWAS) have identified a large number of significant associations between genomic loci and movement disorders such as Parkinson's disease and progressive supranuclear palsy. GWAS are carried out through the use of high-throughput SNP genotyping arrays, which are also used to perform linkage analyses in families previously considered statistically underpowered for genetic analyses. In inherited movement disorders, using this latter technology, it has repeatedly been shown that mutations in a single gene can lead to different phenotypes, while the same clinical entity can be caused by mutations in different genes. This is being highlighted with the use of next-generation sequencing technologies and leads to the search for genes or genetic modifiers that contribute to the phenotypic expression of movement disorders. Establishing an accurate genome-epigenome-phenotype relationship is becoming a major challenge in the post-genomic research that should be facilitated through the implementation of both functional and cellular analyses.

Study of the genetic variability in a Parkinson's Disease gene: EIF4G1

Chartier-Harlin and colleagues [2] recently reported mutations in the eukaryotic translation initiation factor 4-gamma (EIF4G1) gene in families with parkinsonism. Large-scale screening found two mutations (p.R1205H and p.A502V) only in affected individuals, although their relative frequency was very low. The aim of this study was to investigate EIF4G1 parkinsonism-related variants in two separate cohorts and study coding variability across the gene. We first screened a series of familial Parkinson's Disease (PD) patients in an attempt to confirm previous results by showing segregation. Then, to determine the extent of coding variation in the gene, we first screened a cohort of sub-Saharan African individuals from the Centre d’Etude du Polymorphisme Humain – Human Genome Diversity Cell Line Panel (HGDP) [1] and then analyzed data from 5350 individuals National Heart, Lung, and Blood Institute (NHLBI) exome sequencing project. We failed to identify any PD-related mutations in the familial samples. Conversely we found the p.A502V variant in the NHLBI population. We observed a high number of coding polymorphism in the exons where the two PD variants have been previously reported. We conclude that either EIF4G1 variants are an extremely rare cause of familial PD in Caucasian cohorts, or that A502V is in fact a rare benign variant not involved in PD aetiology. Our data also suggests that the protein can tolerate some extent of variability particularly at this point of the gene.