The adult polyglucosan body disease mutation GBE1 c.1076A>C occurs at high frequency in persons of Ashkenazi Jewish background

Case report: Expanding the understanding of the adult polyglucosan body disease continuum: novel presentations, diagnostic pitfalls, and clinical pearls

Introduction: Adult polyglucosan body disease (APBD) has long been regarded as the adult-onset form of glycogen storage disease type IV (GSD IV) and is caused by biallelic pathogenic variants in GBE1. Advances in the understanding of the natural history of APBD published in recent years have led to the use of discrete descriptors ("typical" versus "atypical") based on adherence to traditional symptomatology and homozygosity for the p.Y329S variant. Although these general descriptors are helpful in summarizing common findings and symptoms in APBD, they are inherently limited and may affect disease recognition in diverse populations. Methods: This case series includes three American patients (cases 1-3) and four Brazilian patients (cases 4-7) diagnosed with APBD. Patient-reported outcome (PRO) measures were employed to evaluate pain, fatigue, and quality of life in cases 1-3. Results: We describe the clinical course and diagnostic odyssey of seven cases of APBD that challenge the utility and efficacy of discrete descriptors. Cases 1-3 are compound heterozygotes that harbor the previously identified deep intronic variant in GBE1 and presented with "typical" APBD phenotypically, despite lacking two copies of the pathogenic p.Y329S variant. Patient-reported outcome measures in these three cases revealed the moderate levels of pain and fatigue as well as an impacted quality of life. Cases 4-7 have unique genotypic profiles and emphasize the growing recognition of presentations of APBD in diverse populations with broad neurological manifestations. Conclusion: Collectively, these cases underscore the understanding of APBD as a spectrum disorder existing on the GSD IV phenotypic continuum. We draw attention to the pitfalls of commonly used genetic testing methods when diagnosing APBD and highlight the utility of patient-reported outcome questionnaires in managing this disease.

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

AIMS

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.

METHODS

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).

RESULTS

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.

CONCLUSIONS

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.

Adult polyglucosan body disease: an acute presentation leading to unmasking of this rare disorder

Introduction: Adult polyglucosan body disease (APBD) is an autosomal recessive leukodystrophy caused by abnormal intracellular accumulation of glycogen byproducts. This disorder is linked to a deficiency in glycogen branching enzyme-1 (GBE-1). Neurologic manifestations include upper and lower motor neuron signs, dementia, and peripheral neuropathy. APBD is typically a progressive disease. In this report, we discuss a novel case of APBD in a patient who had a sudden onset of spastic quadriparesis preceded by gradual difficulty with gait. Genetic and postmortem analysis confirmed the diagnosis of APBD.Case report: A 65-year-old man was evaluated for a new-onset of spastic quadriparesis, right-gaze preference, and left-sided beat nystagmus. Magnetic resonance imaging (MRI) of the brain revealed areas of white matter hyperintensities most prominent in the brainstem and periventricular regions. MRI of the cervical spine showed marked cord atrophy. Laboratory workup and cerebrospinal fluid analysis were unremarkable. Genetic testing supported the diagnosis of APBD due to GBE-1 deficiency. Postmortem analysis showed multiple white matter abnormalities suggestive of a leukodystrophy syndrome, and histopathologic testing revealed abnormal accumulation of polyglucosan bodies in samples from the patient's central nervous system supporting the diagnosis of APBD.Conclusion: APBD is a rare disorder that can affect the nervous system. The diagnosis can be confirmed with a combination of genetic testing and pathologic analysis of affected brain tissue.

Intriguing Mixed Pathologic Features in a Case of Dementia With Lewy Bodies

Neuropathologic confirmation of dementia with Lewy bodies (DLB) involves labeling cytoplasmic Lewy body inclusions for α-synuclein in cortical and subcortical neurons. The authors studied the postmortem brain of a 78-year-old man who had a diagnosis of DLB by exclusion. The patient had symptoms ascribed to DLB that included fluctuating cognitive changes in attention and executive function with progression to dementia, visual hallucinations, and parkinsonism. Sections from the olfactory bulbs and cortical and subcortical regions were stained with periodic acid-Schiff, as well as immunolabeled with antibodies specific for α-synuclein, tau protein, β-amyloid 1-42, and Chlamydia pneumoniae. Most regions demonstrated mixed neuropathologic features, and α-synuclein was notable in Lewy bodies in the amygdala and hippocampus. Periodic acid-Schiff-positive staining was noted in bodies in the amygdala and olfactory bulbs. In this case of DLB, neuropathologic inclusions were consistent with the disease diagnosis, but also with Alzheimer disease and other neurodegenerative diseases, such as polyglucosan body disease.

Triacylglycerol mimetics regulate membrane interactions of glycogen branching enzyme: implications for therapy

Adult polyglucosan body disease (APBD) is a neurological disorder characterized by adult-onset neurogenic bladder, spasticity, weakness, and sensory loss. The disease is caused by aberrant glycogen branching enzyme (GBE) (GBE1Y329S) yielding less branched, globular, and soluble glycogen, which tends to aggregate. We explore here whether, despite being a soluble enzyme, GBE1 activity is regulated by protein-membrane interactions. Because soluble proteins can contact a wide variety of cell membranes, we investigated the interactions of purified WT and GBE1Y329S proteins with different types of model membranes (liposomes). Interestingly, both triheptanoin and some triacylglycerol mimetics (TGMs) we have designed (TGM0 and TGM5) markedly enhance GBE1Y329S activity, possibly enough for reversing APBD symptoms. We show that the GBE1Y329S mutation exposes a hydrophobic amino acid stretch, which can either stabilize and enhance or alternatively, reduce the enzyme activity via alteration of protein-membrane interactions. Additionally, we found that WT, but not Y329S, GBE1 activity is modulated by Ca²⁺ and phosphatidylserine, probably associated with GBE1-mediated regulation of energy consumption and storage. The thermal stabilization and increase in GBE1Y329S activity induced by TGM5 and its omega-3 oil structure suggest that this molecule has a considerable therapeutic potential for treating APBD.