Proceedings of the Tenth International Meeting on Neuroacanthocytosis Syndromes

The 10th International Meeting on Neuroacanthocytosis Syndromes was held online on March 10th12th, 2021. The COVID19 pandemic situation made our planned meeting in Barcelona on March 2020 to be suspended by one year, and finally took place online. The meeting followed the previous nine international symposia, the last of which was held in Dresden, Germany in March, 2018. The setting of the meeting encouraged interactions, exchange of ideas and networking opportunities among the high number of participants from around the globe, including scientists, neurologists and specially patients and caregivers. A total of 27 oral communications were distributed in 8 sessions with topics ranging from molecular and cellular functions of VPS13 genes and proteins, their involvement in Neuroacanthocytosis Syndromes and finally clinical aspects and patients care. In addition, 5 posters were presented. Altogether, scientists and neurologists discussed recent advances and set the bases for next steps, action points, and future studies in close collaboration with the patients associations, which are always actively involved in the whole process.


*Author affiliations can be found in the back matter of this article
Proceedings of the Tenth International Meeting on Neuroacanthocytosis Syndromes INTRODUCTION Neuroacanthocytosis syndromes are rare disorders that include acanthocytosis of red blood cells, and neurological manifestations such as chorea, epilepsy, and problems with mood, thinking and memory. Mutations in the VPS13A and XK genes cause chorea-acanthocytosis (ChAc) and McLeod syndrome, respectively. These two syndromes were the focus of most of the talks during the meeting, although the involvement of other VPS13 genes in several "VPS13opathies" were also presented and discussed. Detailed clinical phenotyping, genetic analysis, Western blot diagnosis (in the case of VPS13A) and biomarkers such as creatine kinase (CK) elevation and red blood cell sedimentation, emerged as key elements that might be used to detect, diagnose and follow progression of the syndromes. Common cellular and molecular mechanisms between the different VPS13opathies were present throughout the meeting. These include the role of the different VPS13s in mediating lipid transport in membrane contact sites, as well as their involvement in mitochondria, endoplasmic reticulum, lipid droplet and endosomal functions. Direct interactions between VPS13A and XK proteins may explain some of the common features between ChAc and McLeod syndrome. Also, the relation between VPS13A function and Lyn, PIP3 and IDH3A signaling, together with calcium modulation in the cell may provide potential therapeutic targets for ChAc treatment. Finally, recent insights in VPS13A distribution in the mouse brain, and advances in the phenotyping of mouse models of ChAc, were described and might pave the way for improved understanding ChAc pathophysiology.
At the therapeutic level, outcomes from pharmacological targeting of Lyn kinase and PI3K pathway were detailed, and indicated positive effects in treating red cell blood alterations in patients but not central nervous system symptoms. Deep brain stimulation of globus pallidus was suggested as palliative treatment for patients. Because of the low number of patients worldwide, sharing information regarding patients was encouraged and, in this regard, improvements on the neuroacanthocytosis case registry database were discussed, with the aim of re-activating its use and ensure its continuity for the benefit of all the community. Importantly, patients and caregivers received professional advices for improving their respective quality of lives.
As with our recent symposia, basic scientists and clinicians discussed recent advances and set the bases for next steps, action points, and future studies, in close collaboration with the patient associations, which are always actively involved. which distinguish these disorders from other basal ganglia conditions include seizures and peripheral neuropathy. The typical "rubber person" gait is due to a combination of dystonia, neuropathy, and probably motor impersistence. Dysarthria can be prominent and very disabling. Dysphagia requires ongoing management to minimize risks of aspiration pneumonia. Elevated creatine kinase and liver enzyme abnormalities can suggest either diagnosis. Neuroimaging demonstrates atrophy of the caudate nucleus and putamen. Acanthocytes are variably present and can be absent. Chorea-acanthocytosis is an autosomal recessive syndrome caused by mutations of the gene encoding for the protein chorein. Patients typically present with a combination of symptoms in young adulthood which slowly progress over 1-2 decades. Prominent orofacial dyskinesia and swallowing dystonia suggests the diagnosis, as does self-mutilating tongue-and lip-biting.

Abstract
Chorea-Acanthocytosis (ChAc), one of the core Neuroacanthocytosis syndromes, is an adult-onset rare neurodegenerative disorder caused by alteration in gene VPS13A, one of the four members of the human gene family presenting similarity to yeast VPS13 gene; all of these genes have now been associated with recessive disorders. Extensive screening in affected patients revealed ChAc results from a wide range of pathogenic variations, including large deletions/duplications, splicing-site mutations, small insertions/deletions, nonsense mutations, or missense mutations, with a gene-wide distribution and no hot-spots. These studies provided important insight about this disorder, including the following. First, despite several RNA transcript variants having been described, only the major A variant, originally described as including exons 1-68+70-73, appears to be directly associated with ChAc. Second, most pathogenic variations lead to absence of the VPS13A protein (chorein), confirming that this disease results from loss-of-function of chorein; this allowed to develop a semi-diagnostic test based on the analysis by western blotting of protein extracts from blood, an approach much faster and cheaper than DNA sequencing. Third, a relatively small number of the described pathogenic variations are missense mutations, suggesting that some of the affected residues might be particularly relevant for the function or the stability of chorein. Fourth, despite a number of reports about the occurrence of "dominant ChAc" (patients presenting with ChAc syndrome but having only one VPS13A allele mutated), the current scientific data only support the recessive nature of this condition.
The above points will be among those discussed in a presentation about the current knowledge on the genetics of ChAc in general. As an example to illustrate some of these points, specific details will be presented on the genetics of Spanish patients, one of the largest groups of studied ChAc cases, in which many of the different types of pathogenic variations have been found.

Abstract
As of 2020, with the help of a large group of international colleagues, we have collected blood samples of more than 700 patients with a clinical suspicion of VPS13A disease (formerly chorea-acanthocytosis, ChAc) or related disorders (Danek, Bader & Miltenberger). So far, we confirmed a diagnosis of VPS13A disease by Western blot of the chorein protein in 190 patients. Our free diagnostic chorein Western blot service is generously financed by the Advocacy for Neuroacanthocytosis patients. We have started to compare different protein detection protocols to achieve the most reliable approach for protein-based diagnosis of VPS13A disease. Results from the currently run batch of 80 samples will be presented. In parallel, we analyze the VPS13A gene to gain more information about the associations between genetic changes and chorein levels. In the first analysis of patients with normal chorein (22 cases), we have detected mutations in six patients. In four patients a core neuroacanthocytosis syndrome was diagnosed: in two patients each from mutations in the VPS13A gene (confirming the diagnosis of VPS13A disease) and from mutations in the XK gene, associated with McLeod syndrome. Two patients showed variants in genes associated with other types of movement disorders (KMT2B, GNAL). Overall, we have currently observed six cases with known VPS13A mutations in the presence of normal appearing chorein bands in Western blotting and discuss the details in a dedicated presentation at this meeting (Miltenberger et al.

The role of VPS13C and VPS13D genes in the pathogenesis of movement disorders
Coro Paisán-Ruíz 1 1. Department of Neurology, Icahn School of Medicine at Mount Sinai, New York, USA.

Abstract
Pathogenic genetic variations within VPS13C and VPS13D genes have recently been identified in movement disorder phenotypes. An overview of the disease-associated phenotypes and genetic variations will be summarized here to assist in the clinical diagnosis of prospective patients and families.

Contribution of rare homozygous and compound heterozygous VPS13C missense mutations to dementia with Lewy bodies and Parkinson's disease Abstract
Dementia with Lewy bodies (DLB) and Parkinson's disease (PD) are clinically, pathologically and etiologically disorders embedded in the Lewy body disease (LBD) continuum,1 characterized by neuronal α-synuclein pathology. Rare homozygous and compound heterozygous premature termination codon (PTC) mutations in the Vacuolar Protein Sorting 13 homolog C gene (VPS13C) are associated with early-onset recessive PD. We observed in two siblings with early-onset age (<45) and autopsy confirmed DLB, compound heterozygous missense mutations in VPS13C, p.Trp395Cys and p.Ala444Pro, inherited from their healthy parents in a recessive manner. In lymphoblast cells of the index patient, the missense mutations reduced VPS13C expression by 90% (p = 0.0002). Subsequent, we performed targeted resequencing of VPS13C in 844 LBD patients and 664 control persons. Using the optimized sequence kernel association test, we obtained a significant association (p = 0.0233) of rare VPS13C genetic variants (minor allele frequency ≤ 1%) with LBD. Among the LBD patients, we identified one patient with homozygous missense mutations and three with compound heterozygous missense mutations in trans position, indicative for recessive inheritance. In four patients with compound heterozygous mutations, we were unable to determine trans position. The frequency of LBD patient carriers of proven recessive compound heterozygous missense mutations is 0.59% (5/844). In autopsy brain tissue of two unrelated LBD patients, the recessive compound heterozygous missense mutations reduced VPS13C expression. Overexpressing of wild type or mutant VPS13C in HeLa or SH-SY5Y cells, demonstrated that the mutations p.Trp395Cys or p.Ala444Pro, abolish the endosomal/lysosomal localization of VPS13C. Overall, our data indicate that rare missense mutations in VPS13C are associated with LBD and recessive compound heterozygous missense mutations might have variable effects on the expression and functioning of VPS13C. We conclude that comparable to the recessive inherited PTC mutations in VPS13C, combinations of rare recessive compound heterozygous missense mutations reduce VPS13C expression and contribute to increased risk of LBD.

VPS13 PROTEINS IN CELL PROCESSES
Targeting VPS13 proteins to membrane contact sites Samantha K. Dziurdzik 1 , Michael Davey 1 and Elizabeth Conibear 1 1. Department of Medical Genetics, University of British Columbia, Vancouver, Canada.

Abstract
Mutations in each of the four human VPS13 (VPS13A-D) proteins are associated with distinct neurological disorders: Chorea acanthocytosis, Cohen syndrome, early-onset Parkinson's disease and spastic ataxia. Recent evidence suggests that the different VPS13 paralogs transport lipids between organelles at different membrane contact sites. However, how each VPS13 isoform is targeted to these different sites is not known. Yeast has a single Vps13 protein whose localization depends on developmental stage or nutrient conditions. We have found that the membrane localization of yeast Vps13 requires a conserved six-repeat region, the Vps13 Adaptor Binding (VAB) domain, which binds to organelle-specific adaptors. Our results suggest that all adaptors compete for a single binding site in the VAB domain. Using a systematic mutagenesis strategy to define the contribution of each repeat, we have identified the putative adaptor binding site. Importantly, missense disease-causing mutations are predicted to impact this binding site, suggesting a conserved adaptor binding role for the VAB domain. Current efforts are focused on identifying novel VAB binding partners in both yeast and humans.

Abstract
The VPS13 protein family has been implicated in a variety of cellular function. While in yeast all these functions are performed by a single VPS13 gene, mammalian genomes encode 4 different VPS13 proteins whose physiological roles differ and whose mutations result in distinct, generally severe, clinical conditions. However, as our recent studies suggest, the shared core function of all these proteins, and of the related protein ATG2, is to act as conduits for the bulk flow of lipids at sites of contacts between intracellular membranes. They do so by acting as bridges that tether two adjacent membranes and allow lipid flux along a hydrophobic groove that spans their entire length. Two of the mammalian VPS13 isoforms, VPS13A and VPS13D, whose loss-of-function mutations cause Chorea Acanthocytosis and heterogeneous movement disorders including ataxias, respectively, act at contacts between the ER and mitochondria, although they bind to mitochondria via different mechanisms. Such localization is consistent with the redundant role of yeast VPS13 and ERMES, a protein complex that mediates lipid transport between the ER and mitochondria, even though yeast VPS13 itself populates contact sites other than those between ER and mitochondria (PMID: 26370498; PMID: 27280386). Conserved and redundant roles of VPS13 proteins in mitochondria function underscore the dependence of these organelles, which are excluded from membrane traffic, on protein mediated lipid exchange with other membranes. The two other mammalian VPS13 isoforms, VPS13B and VPS13C, have a different subcellular localization, with VPS13C, whose mutations result in Parkinson's disease,1 acting at contacts between the ER and late-endosomes/lysosomes. In my talk, I will summarize these studies and discuss how these discoveries shed light on mechanisms of disease, with emphasis on Chorea Acanthocytosis.

Abstract
The evolutionary conserved VPS13A gene is associated with the neurodegenerative disorder Chorea Acanthocytosis. We demonstrated that VPS13A is a peripheral membrane protein, associated with mitochondria, the endoplasmic reticulum, and lipid droplets. VPS13A is localized at sites where the endoplasmic reticulum and mitochondria are in close contact. VPS13A interacts with the ER residing protein VAP-A via its FFAT domain. Interaction with mitochondria is mediated via its C-terminal domain. In VPS13A-depleted cells, ER and mitochondria contact sites are decreased, mitochondria are fragmented and mitophagy is decreased. VPS13A also localizes to lipid droplets and affects lipid droplet motility. We further explored possible cellular functions of VPS13A using Drosophila melanogaster with its large cells and versatile genetic tools as a model organism. We demonstrated the presence of increased numbers of lipid droplets in specific brain areas of Vps13 mutants. We also demonstrated that Drosophila Vps13 is required for timely removal of large cellular remnants. During this process a Vps13-rich and Vps13-dependent membranous structure is being formed that surrounds the to-be-degraded cellular remnants. We will discuss how these new data link impairment of Vps13-related proteins with neurodegeneration.

Abstract
VPS13A is a lipid transfer protein that localizes to different membrane contact sites between organelles and its mutation causes the rare disease chorea-acanthocytosis (ChAc). Previous work from our laboratory demonstrated that VPS13A localizes at the interface between mitochondria-endoplasmic reticulum and between mitochondria-endosomes in HeLa cells. Inhibition of VPS13A expression by siRNAs results in defects in lysosome function and accumulation of endolysosomal markers such as RAB7A and LAMP1 (Muñoz-Braceras, S; Tornero-Écija, AR; Vincent, O and Escalante, R. (2019). VPS13A is closely associated with mitochondria and is required for efficient lysosomal degradation. Dis Model Mech. 12(2)(PMID: 30709847). Accumulation of endolysosomal markers could be a useful phenotype for testing compounds in preclinical studies. However, the high cellular variability intrinsically linked to the use of siRNAs prevented us from obtaining conclusive results. We have optimized a CRISPR/Cas9 approach to generate a reliable model to compare wild-type and VPS13A Knock-out HeLa cells. The characterization of this model and preliminary results will be presented.

Abstract
Cohen syndrome (CS) is a rare genetic disorder caused by variations affecting the VPS13B gene. It is characterized by a wide variety of clinical features that includes a typical facial dysmorphism, hypotonia, neutropenia, microcephaly, intellectual disability, and severe visual impairments. Understanding the molecular function of VPS13B is a prerequisite to the development of therapeutic approaches to treat chronic and progressive symptoms of CS. So far, very little is known about VPS13B cellular functions. Based on its domain structure and homologies with the yeast VPS13, VPS13B is likely to play a role in vesicle-mediated sorting and transport of proteins. To study these functions, we produced the Vps13b∆Ex3/∆Ex3 mouse model. Initial phenotyping of the line revealed that male mutant mice were infertile due to morphologically abnormal, nonmotile and short-lived spermatozoa. Histological analysis of the spermiogenesis showed that Vps13b∆Ex3/∆Ex3 spermatids were unable to produce an acrosome, the large nuclear-capping vesicle that contains the hydrolases and other components allowing the sperm nucleus entry into the oocyte. In accordance with previous reports on patient fibroblasts we found that the Golgi apparatus was affected in Vps13b∆Ex3/∆Ex3 spermatids. It lacked the ability to orientate towards the nucleus and surround the nuclear membrane. In addition, marking Golgi-derived vesicles with a lectin (PNA) revealed that instead of being targeted to the nuclear membrane those vesicles were targeted to the early endosome of early spermatids. As spermatids matured, acrosomal vesicles were found enclosed and degraded in lysosomal structures. Altogether, our study shows that Vps13b is an acrosomal membrane protein that redirects Golgi-derived vesicles towards the nuclear membrane. We now investigate whether VPS13B is also an addressing factor for other subsets of vesicles in CSaffected tissues and try to identify the compartments it targets.

Abstract
Insights as to VPS13 function from structural and biochemical studies will be discussed. We found that VPS13 and related proteins may form bridges between membranes of organelles apposed at so-called contact sites that allow for bulk transfer of lipids between them. In this model, VPS13 proteins transfer lipids between the cytosolic leaflets of these membranes. In order to avoid bilayer asymmetry as lipids are depleted or augmented in just one of the leaflets of the donor and acceptor membrane, VPS13 proteins likely cooperate with scramblases that equilibrate lipids between bilayer leaflets.

Using human disease mutations to dissect the functions of yeast Vps13
Jae-Sook Park 1 and Aaron M. Neiman 1 1. Dept. of Biochemistry and Cell Biology, Stony Brook University, USA

Abstract
The large size of the Vps13 protein makes screening for functionally significant missense mutations difficult. Missense alleles identified by sequencing of patients with VPS13-related diseases in humans, therefore, provide a valuable resource to explore structure-function relationships of this protein family. We have introduced mutations in the yeast VPS13 based on alleles found in chorea-acanthocytosis (VPS13A), Cohen syndrome (VPS13B), FTLD (VPS13C), and cerebellar ataxia (VPS13D) patients. Collectively, these mutations occur in different domains across the protein.
Alleles from chorea-acanthocytosis and cerebellar ataxia patients create distinct separation-of-function phenotypes that can be linked to changes in the steadystate distribution of the protein. The combination of either of these alleles with a second, intragenic mutation in VPS13 restores localization and suppresses the mutant phenotypes. The implications of this genetic interaction for the regulation of yeast Vps13 will be discussed.

Abstract
Vps13 are lipid transfer proteins localized in several membrane contact sites, such as nuclear-vacuolar junctions and endosome-mitochondrial junctions. Defects in Vps13(A-D) proteins in humans result in a rare neurodegenerative disease of unknown pathogenesis for which there is no cure. Yeast is a good model system to study function and regulation of Vps13 proteins, the effect of human mutations on cell physiology and to screen for genetic and chemical suppressors of vps13 mutations. In yeast, there is a unique VPS13 gene and its deletion, vps13∆, impairs intracellular trafficking and the actin cytoskeleton, and renders cells hypersensitive to various stress conditions, including sodium dodecyl sulphate (SDS) stress. Using this phenotype we found that vps13 is suppressed by expression of MYO3 fragment encoding N-terminus of myosin which binds calmodulin, RCN2 encoding a negative regulator of calcineurin, a calcium-dependent phosphatase, PMC1 gene for vacuolar calcium transporter, and mutant gene encoding calmodulin. We also found that calcium signaling is increased and calcineurin is hyperactivated in vps13 mutant. Importantly, ethylene glycol tetraacetic acid (EGTA), which sequesters calcium, and FK506 inhibitor of calcineurin were found to be suppressors of vps13 growth defect, pointing to the possible target for chemical intervention in VPS13-related diseases. Furthermore, we found that APT1 domains from yeast Vps13 and human Vps13A bind specific phospholipids and this binding is calcium-dependent. Pathogenic mutation in APT1 domain of Vps13A diminished phospholipid binding and changed its regulation. This supports the view that calcium regulation is also important for functioning of Vps13 proteins and in pathogenesis of VPS13-related diseases. This study was financed by the National Science Centre, Poland (UMO-2015/19/B/NZ3/01515).

Therapeutic Targeting of Lyn Kinase To
Treat ChoreaAcanthocytosis: evidence from pre-clinical studies with (i) accumulation of Lyn, stabilized in high molecular weight complexes; (ii) accumulation of autophagy related proteins; and (iii) reduction in expression of beclin-1, a key initiator of autophagy, due to increased caspase 3 activity. Noteworthy, we also found neuroinflammation in Vps13a -/mice associated with activation of NF-kB p65 and increased expression of IL-1b further emphasizing similarities between ChAc and other neurodegenerative disorders characterized by abnormal proteostasis such as PD or AD. Normalization of phenotypes in the Vps13a -/-Lyn -/double knock out model substantiates the central role of accumulation of active Lyn in the pathophysiology of ChAc. Using proteomic approach, we found accumulation of, alpha-synuclein and phospho-tau proteins in Vps13a -/basal ganglia secondary to impaired autophagy leading to neuroinflammation. Mice double knockout Vps13a -/-Lyn -/showed normalization of red cell morphology and improvement of autophagy in basal ganglia. We then in vivo tested pharmacologic inhibitors of Lyn: Dasatinib and Nilotinib. Dasatinib failed to cross the mouse brain blood barrier (BBB), but the more specific Lyn kinase inhibitor nilotinib, crosses the BBB. Nilotinib ameliorates both Vps13a -/hematological and neurological phenotypes, improving autophagy and preventing neuroinflammation. Our data support the repurposing of nilotinib as new therapeutic option for ChAc patients to be tested in phase II clinical trial.

Abstract
Chorea-acanthocytosis (ChAc) is caused by a VPS13A gene mutation leading to marked reduction or absence of VPS13A protein. ChAc patients show progressive movement disorders such as chorea, dystonia, parkinsonism and involuntary oral biting, among others. Since progressive impairment of basal ganglia circuitry underlie the appearance of movement disorders, it has been proposed that dysfunction of basal ganglia may account for ChAc pathophysiology. Actually, one of the main neuropathologic features in VPS13A mutations is a selective degeneration of the brain striatum. Because of that, a complete characterization of both VPS13A function and ChAc neuropathology in the brain and specifically in striatal neurons is needed. However, there is a poor knowledge about the VPS13A expression in the brain. We analyzed the VPS13A distribution in the mouse basal ganglia and related nuclei. We found a widespread VPS13A distribution along basal ganglia, with low expression levels in the striatum. By contrast we found higher VPS13A expression in the cortex. Thalamic nuclei and substantia nigra presented moderate VPS13A expression. VPS13A was present in glutamatergic pyramidal neurons, but also in some GABAergic neurons. At the subcellular level VPS13A was located in the soma and neurites, interacting with both the endoplasmic reticulum and mitochondria. However, we found no VPS13A within the dendritic spines by immunocytochemistry, which is consistent with the presence but not enrichment of VPS13A we found in cortical synaptosomes. These results indicate that VPS13A has not a direct role in synaptic transmission. However, the relatively low VPS13A expression in the striatum appears to be related with the specific vulnerability of this nucleus to ChAc. Thus, characterization of the molecular and cellular basis of this selective striatal cell loss should report significant progress toward the knowledge of ChAc pathophysiology.
Immunocytochemical study revealed that chorein immunoreactivity is detected only in the mid-piece, mitochondria-rich region, of the sperm of wild type mice. Electron microscopy revealed abnormal ultrastructural morphology of the mitochondria in the mid-piece of sperm from ChAc model mice. The morphological abnormalities were seemed to occur at late stage of mitochondrial sheath developmental process in spermatogenesis. These results suggest that chorein is essential in mouse sperm for the arrangement of mitochondria and sperm motility. In addition, we identified isocitrate dehydrogenase 3 alpha sub unit (IDH3A), a mitochondrial tricarboxylic acid cycle enzyme as a chorein-interacting protein using proteomics analysis following co-immunoprecipitation (co-IP) of mouse sperm. Chorein-1DH3A interaction was also detected in both mouse striatum and Human Embryonic Kidney cells. Western blotting analysis revealed the reduction of immunoreactivities of the IDH3A in ChAc model mouse sperm. Although the relationship between IDH3A reduction and morphological abnormalities of mitochondria in ChAc model mouse remains unclear, it was suggested that chorein, mitochondrial morphology and IDH3A are involved in ChAc pathophysiology.

Abstract
Chorea-Acanthocytosis (ChAc) is an ultra-rare neurodegenerative disease caused by mutations in the VPS13A gene. It is characterized by a spectrum of neurological symptoms (e.g., chorea, epilepsy, parkinsonism, cognitive decline or neuro-/myopathy) and acanthocytosis. It is thus not only a typical differential of Huntington's disease, but also for other disease conditions. Thus, markers which help in the diagnostics of ChAc would be helpful. Furthermore, both pathognomonic markers and markers for clinical progression are of urgent need in case one want to perform clinical trials.
Even though possibly representing with a plethora of clinical phenotypes, there are some which clearly direct us to ChAc. E.g. clinical symptoms such as orolingual biting, tongue protrusions and loss of deep tendon reflexes are typically found in ChAc. Blood cell acanthocytosis clearly helps diagnosing ChAc, but also unexplained and persistent CK elevation independent from activity or seizures in the context of a movement disorder should make us think of ChAc. Of note, however, there is surprisingly little known about the longitudinal behavior during the disease course of all of these clinical and paraclinical "biomarkers" and thus their strength as potential read-outs parameters for disease modifying actions remains elusive.
The talk will give insights in classical and novel potential markers of ChAc. Limited knowledge on the natural history of ChAc remains a barrier for "clinical trial readiness".

Abstract
Establishing a case registry was discussed from the very first symposium in 2002 to define the natural history of neuroacanthocytosis syndromes and to serve as recruitment tool for future therapeutic trials. Set up as a submodule of the European Huntington's Disease Network (www.eurohd.net/html/na/registry), it offers room for an extensive set of patient information. First data were deposited in 2008 and 50+ cases overall were entered. The registry was most active while part of the first EMINA consortium yet has been dormant since. It is a pressing need to revive the registry effort and to tackle open questions. Originally conceived for all "neurocanthocytosis" syndromes, it appears more appropriate to include only cases of chorea-acanthocytosis and of McLeod syndrome, both only with biologically confirmed diagnoses. Ethical and data protection issues must be re-analysed and amended accordingly. Consent forms so far were available only in English. Data monitoring and quality control must be implemented. In addition to clinical data there must be an opportunity to collect imaging data such as from MRI, but also data from wearables and other aspects of "e-health" are of interest. Data-entering colleagues had willingly collaborated but the motivation of busy clinicians must be improved. One possible incentive may be the free diagnostic information (chorein Western blot service) made available by the patient advocacy but also direct financial reimbursement could be considered. Case acquisition might be further improved trough a mechanism for self-registration by patients. Continuous contact and communication will be essential to obtain follow-up data.
The questions of data ownership, data sharing and of publication policies deserve serious effort.
Finally, to secure continuity after 2023 we plan a gradual transition of responsibility from the Munich to the Rostock group.

XK is a partner for VPS13A: A molecular link between Chorea Acanthocytosis and McLeod syndrome
Jae-Sook Park 1 and Aaron M. Neiman 1 1. Dept. of Biochemistry and Cell Biology, Stony Brook University, USA

Abstract
Vps13 is a highly conserved lipid transfer protein found at multiple inter-organelle membrane contact sites. In yeast, the single Vps13 protein is recruited to different contact sites through interaction with different adaptor proteins. Mutations in human VPS13A cause the neurodegenerative disease Chorea Acanthocytosis (ChAc). The symptoms of ChAc resemble those of McLeod syndrome caused by mutations in the XK gene. These observations suggest that XK could be a partner protein for VPS13A. We report that XK forms a complex with VPS13A in human cells, and XK overexpression relocalizes VPS13A from lipid droplets to subdomains of endoplasmic reticulum (ER). A VPS13A protein carrying the ChAc-linked mutation (W2460R) in the VPS13 adaptor binding (VAB) domain failed to localize to lipid droplets and did not relocalize to ER subdomains upon XK overexpression. These observations suggest that the function of VAB domain in regulating VPS13 localization might be conserved in human VPS13A and that disruption of a VPS13A-XK complex is the common basis for ChAc and McLeod syndrome.

Impact of Neuroacanthocytosis syndromes on speech and swallowing function
Background: Speech and communication can be affected at every stage of the disease process, and dysarthria can be one of the earlier symptoms of the disease. Similarly maintaining the safety and pleasure from eating and drinking with family is part of our quality of life. Methods: A combination of anecdotal evidence from short reports and clinical experience shows the wide spectrum and the changes of presentation, from hyperkinetic (too much movement) to hypokinetic (too little). Symptoms affecting speech involve choreic movements of the trunk and the limbs, oro-facio-lingual dyskinesias, limb or facial dystonias, and difficulty initiating movement, with reduced amplitude. Factors contributing to the variability of presentation are age of onset (young adult or middle aged), other treatments (surgical, BOTOX, pharmacological), effect of stress and fatigue, and availability of multidisciplinary team input. Results: The aim of any speech and swallowing intervention is to maintain communication and participation for as long as possible. A variety of speech approaches can be deployed, depending on the stage and the particular symptoms. Sensory tricks can help and need to be acknowledged and expanded. Mouth guards can be useful for tongue dystonia but can impair speech. BOTOX and other pharmacological effects should be monitored for their effects on function before and after their initiation. Working on louder voice can improve not just voice, but articulation clarity. Singing is always beneficial for both the voice and the soul. Voice banking and Alternative communication systems will be discussed.
Swallowing can be affected in the oral stage by the uncontrolled movements of the tongue and the reduced lip seal. Pharyngeal stage can preserve the safety of swallowing. Patients should be encouraged to sit more upright if possible and to minimize distractions during meals. Training the expiratory muscles (with e.g. the EMST150) can help with the cough strength and clearing of saliva. Conclusion: Maintaining communication and swallowing function for as long as possible is paramount. Balancing the hypo-and hyper-kinetic symptoms throughout the disease process requires flexibility and further knowledge, through more longitudinal studies.

POSTER # 1
Detection of PANK2 mutations in the "B siblings" whose Y2721C VPS13A lacks effects in cell models pantothenate kinase associated neurodegeneration. These observations show that a diagnosis of ChAc must ideally be confirmed by reduced chorein expression and/or by proof of clearly pathogenic mutations in both VPS13A alleles. Mere presence of a single mutation with unclear functional effects is clearly insufficient to support the diagnosis POSTER # 2 Characterization of the distribution and localization of VPS13A in the mouse brain to understand the pathophysiology of chorea-acanthocytosis studies, Western blot (WB) analysis of chorein is of great diagnostic value for all suspected cases, in particular when quick diagnosis is required or when genetic studies of the complex VPS13A gene are not easily available. Dobson-Stone et al. (2004) showed that the chorein band detected by WB of erythrocyte (red blood cell, RBC) membranes was absent or severely reduced in VPS13A disease patients, with already confirmed VPS13A mutations. Financially supported by the Advocacy for Neuroacanthocytosis Patients (www.naadvocacy.org) we were able to offer the chorein WB for free as of 2006. Up to now we have received more than 700 samples from patients with a clinical suspicion of chorea-acanthocytosis. In 194 cases, we confirmed a diagnosis of VPS13A disease because of absence or clearly reduced levels of RBC membrane chorein, using a polyclonal antiserum (anti-chor1) against the N-terminal region of chorein (Dobsone-Stone et al. 2004). Interestingly, a number of patients showing normal chorein levels presented with highly suggestive clinical features of VPS13A disease; a genetic follow-up has been started in a number of cases and, so far, pathogenic mutations in VPS13A have been detected in six of them.
Our observations confirm that the chorein WB has less than 100% sensitivity for the diagnosis of VPS13A disease. Thus, they stress the need to follow up on patients with clinical features highly suggestive of VPS13A disease even if chorein WB appeared normal. These observations may relate to properties of the antibody used. Quantitative analyses of the chorein bands are pending. Studying these cases can provide valuable insight about functional domains and stability of chorein