Polyglucosan Body Research Articles

Neuro-Ophthalmic Manifestations of Adult Polyglucosan Body Disease.

Adult polyglucosan body disease (APBD) is caused by a deficiency in glycogen branching enzyme that leads to polyglucosan accumulation in multiple organs. It has a progressive clinical course with prominent neurologic manifestations. We aim to describe the neuro-ophthalmic manifestations of APBD. This is a case series of 3 individuals with genetically proven APBD. Written informed consent was provided by the brothers. We also performed a literature review on the current state of knowledge on APBD through PubMed. Brother 1 developed gait imbalance and length-dependent polyneuropathy in his 40s followed by progressive urinary symptoms in his 50s. He reported diplopia and blurry vision in his 60s. Neuro-ophthalmic assessment revealed bilateral optic neuropathy, convergence insufficiency, and a right fourth nerve palsy. Genetic testing showed a homozygous pathogenic variant in GBE1 c.986A>C p.Tyr329Ser. Brother 2 developed progressive urinary symptoms in his 40s that were followed by cognitive deficits, length-dependent polyneuropathy, and lower extremity weakness in his 50s and 60s. He reported blurred vision, and neuro-ophthalmic evaluation revealed bilateral optic neuropathy. Genetic testing revealed the same variant as Brother 1, GBE1 c.986A>C p.Tyr329Ser. Brother 3 developed progressive urinary urgency and lower extremity weakness in his 50s followed by a length-dependent polyneuropathy in his 60s. He reported diplopia and blurry vision in his 70s. Neuro-ophthalmic assessment revealed bilateral optic neuropathy and convergence insufficiency. Genetic testing revealed the same variant as Brothers 1 and 2, GBE1 c.986A>C p.Tyr329Ser. There is an array of afferent and efferent neuro-ophthalmic manifestations in APBD. Neuro-ophthalmic evaluation is crucial in evaluating and treating patients with APBD, particularly in those with visual dysfunction.

Brainstem Chipmunk Sign: A Diagnostic Imaging Clue across All Subtypes of Alexander Disease.

While classic brain MR imaging features of Alexander disease have been well-documented, lesional patterns can overlap with other leukodystrophies, especially in the early stages of the disease or in milder phenotypes. We aimed to assess the utility of a new neuroimaging sign to help increase the diagnostic specificity of Alexander disease. A peculiar bilateral symmetric hyperintense signal on T2-weighted images affecting the medulla oblongata was identified in an index patient with type I Alexander disease. Subsequently, 5 observers performed a systematic MR imaging review for this pattern by examining 55 subjects with Alexander disease and 74 subjects with other leukodystrophies. Interobserver agreement was assessed by the κ index. Sensitivity, specificity, and receiver operating characteristic curves were determined. The identified pattern was present in 87% of subjects with Alexander disease and 14% of those without Alexander disease leukodystrophy (P < .001), 3 with vanishing white matter, 4 with adult polyglucosan body disease, and 3 others. It was found equally in both type I and type II Alexander disease (28/32, 88% versus 18/21, 86%; P = .851) and in subjects with unusual disease features (2/2). Sensitivity (87.3%; 95% CI, 76.0%-93.7%), specificity (86.5%; 95% CI, 76.9%-92.5%), and interobserver agreement (κ index = 0.82) were high. The identified pattern in the medulla oblongata, called the chipmunk sign due to its resemblance to the face of this rodent, is extremely common in subjects with Alexander disease and represents a diagnostic tool that can aid in early diagnosis, especially in subjects with otherwise atypical MR imaging findings and/or clinical features.

Myofiber-type-dependent 'boulder' or 'multitudinous pebble' formations across distinct amylopectinoses.

At least five enzymes including three E3 ubiquitin ligases are dedicated to glycogen's spherical structure. Absence of any reverts glycogen to a structure resembling amylopectin of the plant kingdom. This amylopectinosis (polyglucosan body formation) causes fatal neurological diseases including adult polyglucosan body disease (APBD) due to glycogen branching enzyme deficiency, Lafora disease (LD) due to deficiencies of the laforin glycogen phosphatase or the malin E3 ubiquitin ligase and type 1 polyglucosan body myopathy (PGBM1) due to RBCK1 E3 ubiquitin ligase deficiency. Little is known about these enzymes' functions in glycogen structuring. Toward understanding these functions, we undertake a comparative murine study of the amylopectinoses of APBD, LD and PGBM1. We discover that in skeletal muscle, polyglucosan bodies form as two main types, small and multitudinous ('pebbles') or giant and single ('boulders'), and that this is primarily determined by the myofiber types in which they form, 'pebbles' in glycolytic and 'boulders' in oxidative fibers. This pattern recapitulates what is known in the brain in LD, innumerable dust-like in astrocytes and single giant sized in neurons. We also show that oxidative myofibers are relatively protected against amylopectinosis, in part through highly increased glycogen branching enzyme expression. We present evidence of polyglucosan body size-dependent cell necrosis. We show that sex influences amylopectinosis in genotype, brain region and myofiber-type-specific fashion. RBCK1 is a component of the linear ubiquitin chain assembly complex (LUBAC), the only known cellular machinery for head-to-tail linear ubiquitination critical to numerous cellular pathways. We show that the amylopectinosis of RBCK1 deficiency is not due to loss of linear ubiquitination, and that another function of RBCK1 or LUBAC must exist and operate in the shaping of glycogen. This work opens multiple new avenues toward understanding the structural determinants of the mammalian carbohydrate reservoir critical to neurologic and neuromuscular function and disease.

A United States-based patient-reported adult polyglucosan body disease registry: initial results.

Adult Polyglucosan Body Disease (APBD) is an ultra-rare, genetic neurodegenerative disorder caused by autosomal recessive mutations in the glycogen branching enzyme gene. Knowledge of the demographic and clinical characteristics of APBD patients and the natural history of the disease is lacking. We report here initial results from a patient-reported registry of APBD patients. (1) Maximize the quality of the APBD Registry survey data; (2) provide an initial report on APBD disease progression and natural history using these data; and (3) specify next steps in the process for testing potential new therapies. Data are from members of the APBD Research Foundation (New York), surveyed from 2014 by the Columbia APBD Patient/Family (CAP) Registry. Inclusion criteria are: disease onset at age 18+ and progressive clinical triad of peripheral neuropathy, spasticity, and neurogenic bladder. Genetic testing results were used when available. Respondents found to not have APBD in clinical records were excluded. All changes and exclusions were recorded in a database edit log. Results are reported in frequency tables, bar graphs, time plots, and heat maps. The 96 respondents meeting inclusion criteria were predominantly (96.8%) White, highly educated (89.3% at least some college education), and mostly (85.1%) of Ashkenazi Jewish descent. 57.1% had at least one parent born in the United States, with at least one grandparent from Europe (excluding Russia; 75.4%), the United States (42.1%), or Russia (33.3%). 37.2% reported a family history of APBD, and 33.3% had an affected sibling. Median APBD onset age was 51 [Interquartile range (IQR) 11], and median age of diagnosis 57 (IQR 10.5). The 75 reported prior misdiagnoses were mainly peripheral neuropathy (43, 60.6%) and spinal stenosis (11, 15.1%). Although from a demographically constricted survey, the results provide basic clinical information for future studies to develop treatments for APBD.

Proteomic investigations of adult polyglucosan body disease: insights into the pathobiology of a neurodegenerative disorder.

Inadequate glycogen branching enzyme 1 (GBE1) activity results in different forms of glycogen storage disease type IV, including adult polyglucosan body disorder (APBD). APBD is clinically characterized by adult-onset development of progressive spasticity, neuropathy, and neurogenic bladder and is histologically characterized by the accumulation of structurally abnormal glycogen (polyglucosan bodies) in multiple cell types. How insufficient GBE1 activity causes the disease phenotype of APBD is poorly understood. We hypothesized that proteomic analysis of tissue from GBE1-deficient individuals would provide insights into GBE1-mediated pathobiology. In this discovery study, we utilized label-free LC-MS/MS to quantify the proteomes of lymphoblasts from 3 persons with APBD and 15 age- and gender-matched controls, with validation of the findings by targeted MS. There were 531 differentially expressed proteins out of 3,427 detected between APBD subjects vs. controls, including pronounced deficiency of GBE1. Bioinformatic analyses indicated multiple canonical pathways and protein-protein interaction networks to be statistically markedly enriched in APBD subjects, including: RNA processing/transport/translation, cell cycle control/replication, mTOR signaling, protein ubiquitination, unfolded protein and endoplasmic reticulum stress responses, glycolysis and cell death/apoptosis. Dysregulation of these processes, therefore, are primary or secondary factors in APBD pathobiology in this model system. Our findings further suggest that proteomic analysis of GBE1 mutant lymphoblasts can be leveraged as part of the screening for pharmaceutical agents for the treatment of APBD.

Mechanistic insights into the homo-dimerization of HOIL-1L and SHARPIN

HOIL-1L and SHARPIN are two essential regulatory subunits of the linear ubiquitin chain assembly complex (LUBAC), which is the only known E3 ligase complex generating linear ubiquitin chains. In addition to their LUBAC-dependent functions, HOIL-1L and SHARPIN alone play crucial roles in many LUBAC-independent cellular processes. Importantly, deficiency of HOIL-1L or SHARPIN leads to severe disorders in humans or mice. However, the mechanistic bases underlying the multi-functions of HOIL-1L and SHARPIN are still largely unknown. Here, we uncover that HOIL-1L and SHARPIN alone can form homo-dimers through their LTM motifs. We solve two crystal structures of the dimeric LTM motifs of HOIL-1L and SHARPIN, which not only elucidate the detailed molecular mechanism underpinning the dimer formations of HOIL-1L and SHARPIN, but also reveal a general mode shared by the LTM motifs of HOIL-1L and SHARPIN for forming homo-dimer or hetero-dimer. Furthermore, we elucidate that the polyglucosan body myopathy-associated HOIL-1L A18P mutation disturbs the structural folding of HOIL-1L LTM, and disrupts the dimer formation of HOIL-1L. In summary, our study provides mechanistic insights into the homo-dimerization of HOIL-1L and SHARPIN mediated by their LTM motifs, and expands our understandings of the multi-functions of HOIL-1L and SHARPIN as well as the etiology of relevant human disease caused by defective HOIL-1L.

Clinical and genetic heterogeneity of adult polyglucosan body disease caused by GBE1 biallelic mutations in China

Clinical and genetic heterogeneity of adult polyglucosan body disease caused by GBE1 biallelic mutations in China

The multifaceted roles of the brain glycogen.

Glycogen is a biologically essential macromolecule that is directly involved in multiple human diseases. While its primary role in carbohydrate storage and energy metabolism in the liver and muscle is well characterized, recent research has highlighted critical metabolic and non-metabolic roles for glycogen in the brain. In this review, the emerging roles of glycogen homeostasis in the healthy and diseased brain are discussed with a focus on advancing our understanding of the role of glycogen in the brain. Innovative technologies that have led to novel insights into glycogen functions are detailed. Key insights into how cellular localization impacts neuronal and glial function are discussed. Perturbed glycogen functions are observed in multiple disorders of the brain, including where it serves as a disease driver in the emerging category of neurological glycogen storage diseases (n-GSDs). n-GSDs include Lafora disease (LD), adult polyglucosan body disease (APBD), Cori disease, Glucose transporter type 1 deficiency syndrome (G1D), GSD0b, and late-onset Pompe disease (PD). They are neurogenetic disorders characterized by aberrant glycogen which results in devastating neurological and systemic symptoms. In the most severe cases, rapid neurodegeneration coupled with dementia results in death soon after diagnosis. Finally, we discuss current treatment strategies that are currently being developed and have the potential to be of great benefit to patients with n-GSD. Taken together, novel technologies and biological insights have resulted in a renaissance in brain glycogen that dramatically advanced our understanding of both biology and disease. Future studies are needed to expand our understanding and the multifaceted roles of glycogen and effectively apply these insights to human disease.

WITHDRAWN: Usefulness of nabilone as an antiemetic in persistent vomiting due to refractory gastrointestinal disorders.

Nabilone, a synthetic analogue of delta-9-Tetrahydrocannabinol, is an agonist of cannabinoid receptors (CB-1 and CB-2) approved to treat chemotherapy-induced vomiting refractory to antiemetics. Its use in patients with refractory vomiting due to gastrointestinal dysmotility (GID) has not been reported. Our study aims are to assess nabilone usefulness and side-effects in patients with refractory vomiting due to GID. Patients prescribed nabilone at St. Mark's intestinal rehabilitation unit (January 2017 to September 2022) due to GID vomiting have been retrospectively reviewed. Descriptive analysis has been done. Variables measured: age, sex, comorbidities, antiemetics/prokinetics, enteral or parenteral nutrition, nabilone prescription, subjective symptom improvement and side-effects. Seven patients received nabilone. 5/7 (72%) were females. Median age:25 years (23-37). 3/7 (43%) had gastroparesis (1/3 related to postural orthostatic tachycardia syndrome -POTS- , 1/3 to Ehlers-Danlos' Syndrome, POTS, Crohn's Disease and adrenal insufficiency -AI- and 1/3 to sinus node ablation and AI), 2/7 (29%) had gastroparesis and intestinal dysmotility (1/2 related to POTS and 1/2 related to EDS and other connective tissue diseases) and 2/7 (29%) had intestinal dysmotility (1/2 because of polyglucosan body visceral myopathy and 1/2 to intestinal surgery). All patients had received antiemetics or prokinetics before (median of 5 drugs; 2-11). 1/7 (14%) received enteral supplements, 5/7 (72%) enteral nutrition through enteral tubes and 4/7 (57%) parenteral nutrition. 5/7 (72%) patients received 1mg of nabilone bd orally, 1/7 (14%) 2 mg bd through jejunostomy and 1/7 (14%) started nabilone at 2 mg bd orally, but had to be switched to 1 mg bd because of side-effects. The median treatment's duration was 9 days (7-35). Regarding the efficacy of nabilone, 3/7 (43%) had symptomatic improvement. In terms of side-effects 4/7 (57%) patients reported some incidence under the treatment such as headache, light-headedness, drowsiness, dizziness or hallucinations. Patients with refractory GID vomiting despite multiple anti-sickness are difficult to treat. Nabilone improved symptoms in almost half of the patients although adverse effects appeared in more than 50%. Doses higher than 1 mg bd po did not show benefit. Although our study has important limitations, nabilone might be a temporary measure in these patients. Side-effects should be taken into consideration.

A Case of HSV-2 Meningitis Retention Syndrome (P12-10.004)

<h3>Objective:</h3> Not applicable <h3>Background:</h3> Meningitis Retention Syndrome (MRS) is a rare disorder characterized by the development of urinary retention in the context of aseptic meningitis with CSF pleocytosis¹. In many cases, no underlying cause is determined, but pathogens such as mycobacteria, listeria, EBV and HSV-2 have been reported as causative agents in the literature². The underlying pathophysiology remains unclear, but possible causes have been suggested including spinal shock secondary to meningeal irritation, sacral myeloradiculitis due to direct viral inflammation, or a post-infectious acute disseminated encephalomyelitis process^3,4. We discuss here an unusual case of a young man presenting for urinary retention who was found to have HSV-2 meningitis. <h3>Design/Methods:</h3> <h3>Case report:</h3> A 17-year-old male with chronic constipation presented to the emergency department for urinary retention of 2 days duration. He endorsed the sensation to void with an inability to empty his bladder despite straining in the setting of a two-week history of mild headaches, diffuse back pain, myalgias and low-grade fevers. He was non-toxic appearing and neurological exam was normal. Abdominal X-ray showed a moderate stool burden. Spine MRI demonstrated subtle enhancement of the cauda equina. CSF evaluation were notable for an elevated opening pressure to 34 mmHg and a lymphocytic pleocytosis (693 white blood cells), and elevated protein of 60. Multiplex panel for central nervous system infections by polymerase chain reaction was positive for HSV-2. He was admitted to the hospital for IV acyclovir and management of urinary retention. <h3>Results:</h3> Not applicable <h3>Conclusions:</h3> This case demonstrated the importance of keeping meningitis retention syndrome on the differential for individuals presenting with acute urinary retention after a viral infection. Keeping a high index of suspicion is crucial, especially in cases like the one described where the patient only had some vague viral symptoms but no obvious meningeal signs, radicular pains or genital ulcers. <b>Disclosure:</b> Dr. Aoun has nothing to disclose. Dr. Raj Ghosh has nothing to disclose. Dr. Kuball has nothing to disclose. The institution of Dr. Abreu has received research support from Adult Polyglucosan Body Disease Research Foundation. The institution of Dr. Abreu has received research support from Sanofi Genzyme. The institution of Dr. Abreu has received research support from Takeda. The institution of Dr. Abreu has received research support from Sangamo.

Prevalence of Peripheral Nervous System Involvement in Adult Leukodystrophies (P2-5.031)

<h3>Objective:</h3> na <h3>Background:</h3> Leukodystrophies are genetic, neurodegenerative white matter diseases of the central nervous system (CNS) caused by mutations in various genes, presenting with heterogeneous clinical features and age of onset. It is well established that some leukodystrophies have peripheral nervous system (PNS) involvement, whether demyelinating, axonal or mixed in pathology. However, the prevalence of peripheral neuropathy in adult leukodystrophies is unknown. Early recognition of PNS involvement in these disorders is imperative to enable appropriate management and care of the symptoms. <h3>Design/Methods:</h3> We performed a retrospective review of all adult subjects followed at our two institutions for white matter disease of genetic origin to select patients with evidence of PNS involvement as documented by nerve conduction studies (NCS) and/or electromyography (EMG)For these subjects we collected and analyzed data on sociodemographic status, family history, clinical characteristics, and disease course, nerve conduction studies (NCS), electromyography (EMG), MRI features and genetic testing results. <h3>Results:</h3> From our combined cohorts of 161 adult subjects followed for genetic white matter diseases, we identified 14 patients (8.7%) with documented PNS involvement. A definite genetic diagnosis was established in 5 subjects (3 with adult polyglucosan body disease, 1 with metachromatic leukodystrophy, 1 with POLR3-related disorder) while 9 subjects remained undiagnosed despite extensive genetic investigations. The demographic, clinical, radiological, and electrophysiological data will be presented. <h3>Conclusions:</h3> This is the first study conducted to assess the prevalence of peripheral neuropathy in adult patients with leukodystrophy. In our two independent cohorts, PNS involvement is rare, however, early recognition of the concurrence of CNS and PNS involvement is essential to plan appropriate management of the patients’ symptomatic care and is key as more treatment options are becoming available. <b>Disclosure:</b> Dr. Alsabah has nothing to disclose. Dr. Hasiloglu has nothing to disclose. Dr. Massie has received personal compensation in the range of $500-$4,999 for serving as a Expert consultant with INESS (Quebec Public Health agency). Dr. Massie has received personal compensation in the range of $500-$4,999 for serving as a Lecturer with Amylyx Pharmaceuticals. Dr. Brais has nothing to disclose. Dr. Orthmann Murphy has received research support from Conrad N. Hilton Foundation. Dr. Orthmann Murphy has received research support from Institute for Translational Medicine and Therapeutics’ (ITMAT) Transdisciplinary Program in Translational Medicine and Therapeutics, University of Pennsylvania. The institution of Dr. Orthmann Murphy has received research support from Vigil Neurosciences. The institution of Dr. Orthmann Murphy has received research support from National MS Society. Dr. Orthmann Murphy has received personal compensation in the range of $500-$4,999 for serving as a Invited Speaker with Temple University . Dr. Orthmann Murphy has received personal compensation in the range of $0-$499 for serving as a Consultant with American Neurological Association. Roberta La Piana has nothing to disclose.

Teaching Neuro Images : Prominent spinal cord atrophy and white matter changes in adult polyglucosan body disease

A 48-year-old man of Ashkenazi Jewish descent developed neurogenic bladder and mild cognitive dysfunction. Neurologic examination and CSF analysis were unremarkable. Brain MRI demonstrated white matter changes in the internal capsule, optic radiations, mesencephalon, superior cerebellar peduncles, pons, and medulla (figure 1) and prominent medullary and spinal cord atrophy (figure 2). These findings are classically found in adult polyglucosan body disease (APBD).1 Glycogen branching enzyme GBE1 gene sequencing revealed that the patient was compound heterozygous (c.691+2T>C and c.986 A>C). APBD should be considered in patients with adult-onset leukodystrophy and spinal atrophy; genetic testing is crucial to prevent misdiagnosis with multiple sclerosis and other leukodystrophies.2

Diagnosis and management of glycogen storage disease type IV, including adult polyglucosan body disease: A clinical practice resource.

Glycogen storage disease type IV (GSD IV) is an ultra-rare autosomal recessive disorder caused by pathogenic variants in GBE1 which results in reduced or deficient glycogen branching enzyme activity. Consequently, glycogen synthesis is impaired and leads to accumulation of poorly branched glycogen known as polyglucosan. GSD IV is characterized by a remarkable degree of phenotypic heterogeneity with presentations in utero, during infancy, early childhood, adolescence, or middle to late adulthood. The clinical continuum encompasses hepatic, cardiac, muscular, and neurologic manifestations that range in severity. The adult-onset form of GSD IV, referred to as adult polyglucosan body disease (APBD), is a neurodegenerative disease characterized by neurogenic bladder, spastic paraparesis, and peripheral neuropathy. There are currently no consensus guidelines for the diagnosis and management of these patients, resulting in high rates of misdiagnosis, delayed diagnosis, and lack of standardized clinical care. To address this, a group of experts from the United States developed a set of recommendations for the diagnosis and management of all clinical phenotypes of GSD IV, including APBD, to support clinicians and caregivers who provide long-term care for individuals with GSD IV. The educational resource includes practical steps to confirm a GSD IV diagnosis and best practices for medical management, including (a) imaging of the liver, heart, skeletal muscle, brain, and spine, (b) functional and neuromusculoskeletal assessments, (c) laboratory investigations, (d) liver and heart transplantation, and (e) long-term follow-up care. Remaining knowledge gaps are detailed to emphasize areas for improvement and future research.

Role of Astrocytes in the Pathophysiology of Lafora Disease and Other Glycogen Storage Disorders.

Lafora disease is a rare disorder caused by loss of function mutations in either the EPM2A or NHLRC1 gene. The initial symptoms of this condition are most commonly epileptic seizures, but the disease progresses rapidly with dementia, neuropsychiatric symptoms, and cognitive deterioration and has a fatal outcome within 5-10 years after onset. The hallmark of the disease is the accumulation of poorly branched glycogen in the form of aggregates known as Lafora bodies in the brain and other tissues. Several reports have demonstrated that the accumulation of this abnormal glycogen underlies all the pathologic traits of the disease. For decades, Lafora bodies were thought to accumulate exclusively in neurons. However, it was recently identified that most of these glycogen aggregates are present in astrocytes. Importantly, astrocytic Lafora bodies have been shown to contribute to pathology in Lafora disease. These results identify a primary role of astrocytes in the pathophysiology of Lafora disease and have important implications for other conditions in which glycogen abnormally accumulates in astrocytes, such as Adult Polyglucosan Body disease and the buildup of Corpora amylacea in aged brains.

Abundant copathologies of polyglucosan bodies, frontotemporal lobar degeneration with TDP-43 inclusions and ageing-related tau astrogliopathy in a family with a GBE1 mutation.

Adult polyglucosan body disease (APBD) is a progressive neurogenetic disorder caused by 1,4-alpha-glucan branching enzyme 1 (GBE1) mutation with an accumulation of polyglucosan bodies (PBs) in the central and peripheral nervous systems as a pathological hallmark. Here, we report two siblings in a family with a GBE1 mutation with prominent frontotemporal lobar degeneration with TAR DNA-binding protein 43 (FTLD-TDP) and ageing-related tau astrogliopathy (ARTAG) copathologies with PBs in the central nervous system. Whole-genome sequencing (WGS) followed by Sanger sequencing (SS) was performed on three affected and two unaffected siblings in a pedigree diagnosed with familial frontotemporal dementia. Out of the affected siblings, autopsies were conducted on two cases, and brain samples were used for biochemical and histological analyses. Brain sections were stained with haematoxylin and eosin and immunostained with antibodies against ubiquitin, tau, amyloid β, α-synuclein, TDP-43 and fused in sarcoma (FUS). A novel single nucleotide deletion in GBE1, c.1280delG, was identified, which is predicted to result in a reading frameshift, p.Gly427Glufs*9. This variant segregated with disease in the family, is absent from population databases and is predicted to cause loss of function, a known genetic mechanism for APBD. The affected siblings showed a greater than 50% decrease in GBE protein levels. Immunohistochemical analysis revealed widespread FTLD-TDP (type A) and ARTAG pathologies as well as PBs in the brains of two affected siblings for whom an autopsy was performed. This is the first report of a family with several individuals with a FTD clinical phenotype and underlying copathologies of APBD, FTLD-TDP and ARTAG with a segregating GBE1 loss-of-function mutation in affected siblings. The finding of copathologies of APBD and FTLD-TDP suggests these processes may share a disease mechanism resulting from this GBE1 mutation.

P158: The diagnostic odyssey: A review of two patients with adult polyglucosan body disease

P158: The diagnostic odyssey: A review of two patients with adult polyglucosan body disease

Pathomorphogenesis of Glycogen-Ground Glass Hepatocytic Inclusions (Polyglucosan Bodies) in Children after Liver Transplantation.

Seventeen out of 764 liver biopsies from transplanted (Tx) livers in children showed glycogen-ground glass (GGG) hepatocytic inclusions. The inclusions were not present in pre-Tx or in the explanted or donor’s liver. Under the electron microscope (EM), the stored material within the cytosol appeared as non-membrane-bound aggregates of electron-lucent globoid or fibrillar granules, previously described as abnormally structured glycogen and identified as Polyglucosan bodies (PB). The appearance of GGG in our children was analogous to that of PB-GGG occurring in a number of congenital diseases due to gene mutations such as Lafora’s d., Andersen’s d., Adult Polyglucosan Body Disease and glycogenin deficiency. The same type of GGG was previously reported in the liver of patients undergoing transplants, immunosuppressive or antiblastic treatment. To explore the potential mechanism of GGG formation, we examined whether the drugs after whose treatment this phenomenon was observed could have a role. By carrying out molecular docking, we found that such drugs somehow present a high binding affinity for the active region of glycogenin, implicating that they can inactivate the protein, thus preventing its interaction with glycogen synthase (GS), as well as the maturation of the nascent glycogen towards gamma, beta or alfa glycogen granules. We could also demonstrate that PG inclusions consist of a complex of PAS positive material (glycogen) and glycogen-associated proteins, i.e., glicogenin-1 and -2 and ubiquitin. These features appear to be analogous to congenital GGG, suggesting that, in both cases, they result from the simultaneous dysregulation of glycogen synthesis and degradation. Drug-induced GGG appear to be toxic to the cell, despite their reversibility.

RBCK1-Associated Polyglucosan Body Myopathy Presenting with Mild Weakness and Pain: A Case Report (P16-13.007)

RBCK1-Associated Polyglucosan Body Myopathy Presenting with Mild Weakness and Pain: A Case Report (P16-13.007)

AAV-Mediated Artificial miRNA Reduces Pathogenic Polyglucosan Bodies and Neuroinflammation in Adult Polyglucosan Body and Lafora Disease Mouse Models

Adult polyglucosan body disease (APBD) and Lafora disease (LD) are autosomal recessive glycogen storage neurological disorders. APBD is caused by mutations in the glycogen branching enzyme (GBE1) gene and is characterized by progressive upper and lower motor neuron dysfunction and premature death. LD is a fatal progressive myoclonus epilepsy caused by loss of function mutations in the EPM2A or EPM2B gene. These clinically distinct neurogenetic diseases share a common pathology. This consists of time-dependent formation, precipitation, and accumulation of an abnormal form of glycogen (polyglucosan) into gradually enlarging inclusions, polyglucosan bodies (PBs) in ever-increasing numbers of neurons and astrocytes. The growth and spread of PBs are followed by astrogliosis, microgliosis, and neurodegeneration. The key defect in polyglucosans is that their glucan branches are longer than those of normal glycogen, which prevents them from remaining in solution. Since the lengths of glycogen branches are determined by the enzyme glycogen synthase, we hypothesized that downregulating this enzyme could prevent or hinder the generation of the pathogenic PBs. Here, we pursued an adeno-associated virus vector (AAV) mediated RNA-interference (RNAi) strategy. This approach resulted in approximately 15% reduction of glycogen synthase mRNA and an approximately 40% reduction of PBs across the brain in the APBD and both LD mouse models. This was accompanied by improvements in early neuroinflammatory markers of disease. This work represents proof of principle toward developing a single lifetime dose therapy for two fatal neurological diseases: APBD and LD. The approach is likely applicable to other severe and common diseases of glycogen storage.

Glycogen synthase downregulation rescues the amylopectinosis of murine RBCK1 deficiency.

Longer glucan chains tend to precipitate. Glycogen, by far the largest mammalian glucan and the largest molecule in the cytosol with up to 55 000 glucoses, does not, due to a highly regularly branched spherical structure that allows it to be perfused with cytosol. Aberrant construction of glycogen leads it to precipitate, accumulate into polyglucosan bodies that resemble plant starch amylopectin and cause disease. This pathology, amylopectinosis, is caused by mutations in a series of single genes whose functions are under active study toward understanding the mechanisms of proper glycogen construction. Concurrently, we are characterizing the physicochemical particularities of glycogen and polyglucosans associated with each gene. These genes include GBE1, EPM2A and EPM2B, which respectively encode the glycogen branching enzyme, the glycogen phosphatase laforin and the laforin-interacting E3 ubiquitin ligase malin, for which an unequivocal function is not yet known. Mutations in GBE1 cause a motor neuron disease (adult polyglucosan body disease), and mutations in EPM2A or EPM2B a fatal progressive myoclonus epilepsy (Lafora disease). RBCK1 deficiency causes an amylopectinosis with fatal skeletal and cardiac myopathy (polyglucosan body myopathy 1, OMIM# 615895). RBCK1 is a component of the linear ubiquitin chain assembly complex, with unique functions including generating linear ubiquitin chains and ubiquitinating hydroxyl (versus canonical amine) residues, including of glycogen. In a mouse model we now show (i) that the amylopectinosis of RBCK1 deficiency, like in adult polyglucosan body disease and Lafora disease, affects the brain; (ii) that RBCK1 deficiency glycogen, like in adult polyglucosan body disease and Lafora disease, has overlong branches; (iii) that unlike adult polyglucosan body disease but like Lafora disease, RBCK1 deficiency glycogen is hyperphosphorylated; and finally (iv) that unlike laforin-deficient Lafora disease but like malin-deficient Lafora disease, RBCK1 deficiency's glycogen hyperphosphorylation is limited to precipitated polyglucosans. In summary, the fundamental glycogen pathology of RBCK1 deficiency recapitulates that of malin-deficient Lafora disease. Additionally, we uncover sex and genetic background effects in RBCK1 deficiency on organ- and brain-region specific amylopectinoses, and in the brain on consequent neuroinflammation and behavioural deficits. Finally, we exploit the portion of the basic glycogen pathology that is common to adult polyglucosan body disease, both forms of Lafora disease and RBCK1 deficiency, namely overlong branches, to show that a unified approach based on downregulating glycogen synthase, the enzyme that elongates glycogen branches, can rescue all four diseases.