Induced pluripotent stem cell (iPSC) modeling validates reduced GBE1 enzyme activity due to a novel variant, p.Ile694Asn, found in a patient with suspected glycogen storage disease IV

Background

Glycogen Storage disease type 4 (GSD4), a rare disease caused by glycogen branching enzyme 1 (GBE1) deficiency, affects multiple organ systems including the muscles, liver, heart, and central nervous system. Here we report a GSD4 patient, who presented with severe hepatosplenomegaly and cardiac ventricular hypertrophy. GBE1 sequencing identified two variants: a known pathogenic missense variant, c.1544G>A (p.Arg515His), and a missense variant of unknown significance (VUS), c.2081T>A (p. Ile694Asn). As a liver transplant alone can exacerbate heart dysfunction in GSD4 patients, a precise diagnosis is essential for liver transplant indication. To characterize the disease-causing variant, we modeled patient-specific GBE1 deficiency using CRISPR/Cas9 genome-edited induced pluripotent stem cells (iPSCs).

Methods

iPSCs from a healthy donor (iPSC-WT) were genome-edited by CRISPR/Cas9 to induce homozygous p.Ile694Asn in GBE1 (iPSC-GBE1-I694N) and differentiated into hepatocytes (iHep) or cardiomyocytes (iCM). GBE1 enzyme activity was measured, and PAS-D staining was performed to analyze polyglucosan deposition in these cells.

Results

iPSCGBE1-I694N differentiated into iHep and iCM exhibited reduced GBE1 protein level and enzyme activity in both cell types compared to iPSCwt. Both iHepGBE1-I694N and iCMGBE1-I694N showed polyglucosan deposits correlating to the histologic patterns of the patient's biopsies.

Conclusions

iPSC-based disease modeling supported a loss of function effect of p.Ile694Asn in GBE1. The modeling of GBE1 enzyme deficiency in iHep and iCM cell lines had multi-organ findings, demonstrating iPSC-based modeling usefulness in elucidating the effects of novel VUS in ultra-rare diseases.

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

Background

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.

Objectives

(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.

Design

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.

Methods

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.

Results

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%).

Conclusion

Although from a demographically constricted survey, the results provide basic clinical information for future studies to develop treatments for APBD.

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.

Case 318: Adult Polyglucosan Body Disease

HISTORY

A 72-year-old man sought care for a cognitive deterioration over the past 5 years. There was a documented decline in his performance on the Mini-Mental State Examination (30 of 30 in 2016, 23 of 30 in 2021), with mainly episodic memory impairment. A more detailed history revealed a gait problem, paresthesia in both feet, and nocturnal urinary frequency. Clinical examination findings were suggestive of a length-dependent polyneuropathy. In addition, a right-sided Babinski sign was noted. Electromyography and a nerve conduction study corroborated a peripheral axonal sensorimotor neuropathy. MRI of the brain was performed.

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.

GBE1-related disorders: Adult polyglucosan body disease and its neuromuscular phenotypes

Adult polyglucosan body disease (APBD) represents a complex autosomal recessive inherited neurometabolic disorder due to homozygous or compound heterozygous pathogenic variants in GBE1 gene, resulting in deficiency of glycogen-branching enzyme and secondary storage of glycogen in the form of polyglucosan bodies, involving the skeletal muscle, diaphragm, peripheral nerve (including autonomic fibers), brain white matter, spinal cord, nerve roots, cerebellum, brainstem and to a lesser extent heart, lung, kidney, and liver cells. The diversity of new clinical presentations regarding neuromuscular involvement is astonishing and transformed APBD in a key differential diagnosis of completely different clinical conditions, including axonal and demyelinating sensorimotor polyneuropathy, progressive spastic paraparesis, motor neuronopathy presentations, autonomic disturbances, leukodystrophies or even pure myopathic involvement with limb-girdle pattern of weakness. This review article aims to summarize the main clinical, biochemical, genetic, and diagnostic aspects regarding APBD with special focus on neuromuscular presentations.

Adult polyglucosan body disease-an atypical compound heterozygous with a novel GBE1 mutation

INTRODUCTION

Adult polyglucosan body disease (APBD) is an autosomal recessive leukodystrophy characterized by neurogenic bladder starting after 40 years old, spastic paraparesis and peripheral neuropathy. It is mainly resultant from the GBE1 homozygous p.Tyr329Ser (c.986A>C) mutation, especially in Ashkenazi-Jewish patients, although some cases of compound heterozygous have been reported. A genotype-phenotype correlation is not established, but atypical phenotypes have been described mainly in non-p.Tyr329Ser pathogenic variants.

CASE REPORT

We describe an atypical case in a 62-year-old Portuguese woman, presenting the typical clinical triad of APBD plus prominent autonomic dysfunction, suggested by orthostatic hypotension and thermoregulatory dysfunction; she has compound heterozygous GBE1 mutations, namely, p.Asn541Asp (c.1621A>G) and p.Arg515Gly (c.1543C>G), the last one not yet reported in literature and whose pathogenicity was suggested by bioinformatics analysis and confirmed by sural nerve biopsy that showed intra-axonal polyglucosan bodies.

DISCUSSION

Besides the report of a novel GBE1 mutation, this case also expands the phenotypic spectrum of this disorder, reinforcing autonomic dysfunction as a possible and prominent manifestation of APBD, mimicking autosomal dominant leukodystrophy with autonomic disease in some way. Therefore, we questioned a possible relationship between this genotype and the phenotype marked by dysautonomia. Additionally, we review previously reported cases of APBD in non-homozygous p.Tyr329Ser patients with atypical phenotypes.

Analysis of GBE1 mutations via protein expression studies in glycogen storage disease type IV: A report on a non-progressive form with a literature review

Background

Glycogen storage disease type IV (GSD IV), caused by GBE1 mutations, has a quite wide phenotypic variation. While the classic hepatic form and the perinatal/neonatal neuromuscular forms result in early mortality, milder manifestations include non-progressive form (NP-GSD IV) and adult polyglucosan body disease (APBD). Thus far, only one clinical case of a patient with compound heterozygous mutations has been reported for the molecular analysis of NP-GSD IV. This study aimed to elucidate the molecular basis in a NP-GSD IV patient via protein expression analysis and to obtain a clearer genotype-phenotype relationship in GSD IV.

Case presentation

A Japanese boy presented hepatosplenomegaly at 2 years of age. Developmental delay, neurological symptoms, and cardiac dysfunction were not apparent. Observation of hepatocytes with periodic acid-Schiff-positive materials resistant to diastase, coupled with resolution of hepatosplenomegaly at 8 years of age, yielded a diagnosis of NP-GSD IV. Glycogen branching enzyme activity was decreased in erythrocytes. At 13 years of age, he developed epilepsy, which was successfully controlled by carbamazepine.

Molecular analysis

In this study, we identified compound heterozygous GBE1 mutations (p.Gln46Pro and p.Glu609Lys). The branching activities of the mutant proteins expressed using E. coli were examined in a reaction with starch. The result showed that both mutants had approximately 50% activity of the wild type protein.

Conclusion

This is the second clinical report of a NP-GSD IV patient with a definite molecular elucidation. Based on the clinical and genotypic overlapping between NP-GSD IV and APBD, we suggest both are in a continuum.

Adult polyglucosan body disease: Natural History and Key Magnetic Resonance Imaging Findings

OBJECTIVE

Adult polyglucosan body disease (APBD) is an autosomal recessive leukodystrophy characterized by neurogenic bladder, progressive spastic gait, and peripheral neuropathy. Polyglucosan bodies accumulate in the central and peripheral nervous systems and are often associated with glycogen branching enzyme (GBE) deficiency. To improve clinical diagnosis and enable future evaluation of therapeutic strategies, we conducted a multinational study of the natural history and imaging features of APBD.

METHODS

We gathered clinical, biochemical, and molecular findings in 50 APBD patients with GBE deficiency from Israel, the United States, France, and the Netherlands. Brain and spine magnetic resonance images were reviewed in 44 patients.

RESULTS

The most common clinical findings were neurogenic bladder (100%), spastic paraplegia with vibration loss (90%), and axonal neuropathy (90%). The median age was 51 years for the onset of neurogenic bladder symptoms, 63 years for wheelchair dependence, and 70 years for death. As the disease progressed, mild cognitive decline may have affected up to half of the patients. Neuroimaging showed hyperintense white matter abnormalities on T2 and fluid attenuated inversion recovery sequences predominantly in the periventricular regions, the posterior limb of the internal capsule, the external capsule, and the pyramidal tracts and medial lemniscus of the pons and medulla. Atrophy of the medulla and spine was universal. p.Y329S was the most common GBE1 mutation, present as a single heterozygous (28%) or homozygous (48%) mutation.

INTERPRETATION

APBD with GBE deficiency, with occasional exceptions, is a clinically homogenous disorder that should be suspected in patients with adult onset leukodystrophy or spastic paraplegia with early onset of urinary symptoms and spinal atrophy.

Whole exome sequencing in foetal akinesia expands the genotype-phenotype spectrum of GBE1 glycogen storage disease mutations

The clinically and genetically heterogenous foetal akinesias have low rates of genetic diagnosis. Exome sequencing of two siblings with phenotypic lethal multiple pterygium syndrome identified compound heterozygozity for a known splice site mutation (c.691+2T>C) and a novel missense mutation (c.956A>G; p.His319Arg) in glycogen branching enzyme 1 (GBE1). GBE1 mutations cause glycogen storage disease IV (GSD IV), including a severe foetal akinesia sub-phenotype. Re-investigating the muscle pathology identified storage material, consistent with GSD IV, which was confirmed biochemically. This study highlights the power of exome sequencing in genetically heterogeneous diseases and adds multiple pterygium syndrome to the phenotypic spectrum of GBE1 mutation.

Acute but transient neurological deterioration revealing adult polyglucosan body disease

Adult polyglucosan body disease (APBD) is a metabolic disorder usually caused by glycogen branching enzyme (GBE) deficiency. APBD associates progressive walking difficulties, bladder dysfunction and, in about 50% of the cases, cognitive decline. APBD is characterized by a recognizable leukodystrophy on brain MRI. We report here a novel presentation of this disease in a 35-year old woman who presented with an acute deterioration followed by an unexpected recovery. Enzymatic analysis displayed decreased GBE activity in leukocytes. Molecular analyses revealed that only one mutated allele was expressed, bearing a p.Arg515His mutation. This is the first observation reporting acute and reversible neurological symptoms in APBD. These findings emphasize the importance of searching GBE deficiency in patients presenting with a leukodystrophy and acute neurological symptoms mimicking a stroke, in the absence of cardiovascular risk factors.

Glycogen storage disease type IV: novel mutations and molecular characterization of a heterogeneous disorder

Glycogen storage disease type IV (GSD IV; Andersen disease) is caused by a deficiency of glycogen branching enzyme (GBE), leading to excessive deposition of structurally abnormal, amylopectin-like glycogen in affected tissues. The accumulated glycogen lacks multiple branch points and thus has longer outer branches and poor solubility, causing irreversible tissue and organ damage. Although classic GSD IV presents with early onset of hepatosplenomegaly with progressive liver cirrhosis, GSD IV exhibits extensive clinical heterogeneity with respect to age at onset and variability in pattern and extent of organ and tissue involvement. With the advent of cloning and determination of the genomic structure of the human GBE gene (GBE1), molecular analysis and characterization of underlying disease-causing mutations is now possible. A variety of disease-causing mutations have been identified in the GBE1 gene in GSD IV patients, many of whom presented with diverse clinical phenotypes. Detailed biochemical and genetic analyses of three unrelated patients suspected to have GSD IV are presented here. Two novel missense mutations (p.Met495Thr and p.Pro552Leu) and a novel 1-bp deletion mutation (c.1999delA) were identified. A variety of mutations in GBE1 have been previously reported, including missense and nonsense mutations, nucleotide deletions and insertions, and donor and acceptor splice-site mutations. Mutation analysis is useful in confirming the diagnosis of GSD IV--especially when higher residual GBE enzyme activity levels are seen and enzyme analysis is not definitive--and allows for further determination of potential genotype/phenotype correlations in this disease.

Congenital type IV glycogenosis: the spectrum of pleomorphic polyglucosan bodies in muscle, nerve, and spinal cord with two novel mutations in the GBE1 gene

A diagnosis of GSD-IV was established in three premature, floppy infants based on characteristic, however unusually pleomorphic polyglucosan bodies at the electron microscopic level, glycogen branching enzyme deficiency in two cases, and the identification of GBE1 mutations in two cases. Pleomorphic polyglucosan bodies in muscle fibers and macrophages, and less severe in Schwann cells and microglial cells were noted. Most of the inclusions were granular and membrane-bound; others had an irregular contour, were more electron dense and were not membrane bound, or homogenous ('hyaline'). A paracrystalline pattern of granules was repeatedly noted showing a periodicity of about 10 nm with an angle of about 60 degrees or 120 degrees at sites of changing linear orientation. Malteser crosses were noted under polarized light in the larger inclusions. Some inclusions were PAS positive and others were not. Severely atrophic muscle fibers without inclusions, but with depletion of myofibrils in the plane of section studied indicated the devastating myopathic nature of the disease. Schwann cells and peripheral axons were less severely affected as was the spinal cord. Two novel protein-truncating mutations (c.1077insT, p.V359fsX16; g.101517_127067del25550insCAGTACTAA, DelExon4-7) were identified in these families. The present findings extend previous studies indicating that truncating GBE1 mutations cause a spectrum of severe diseases ranging from generalized intrauterine hydrops to fatal perinatal hypotonia and fatal cardiomyopathy in the first months of life.

Leukoencephalopathies associated with inborn errors of metabolism in adults

The discovery of a leukoencephalopathy is a frequent situation in neurological practice and the diagnostic approach is often difficult given the numerous possible aetiologies, which include multiple acquired causes and genetic diseases including inborn errors of metabolism (IEMs). It is now clear that IEMs can have their clinical onset from early infancy until late adulthood. These diseases are particularly important to recognize because specific treatments often exist. In this review, illustrated by personal observations, we give an overview of late-onset leukoencephalopathies caused by IEMs.

Movement disorders and inborn errors of metabolism in adults: a diagnostic approach

Inborn errors of metabolism (IEMs) may present in adolescence or adulthood with various movement disorders including parkinsonism, dystonia, chorea, tics or myoclonus. Main diseases causing movement disorders are metal-storage diseases, neurotransmitter synthesis defects, energy metabolism disorders and lysosomal storage diseases. IEMs should not be missed as many are treatable. Here we briefly review IEMs causing movement disorders in adolescence and adults and propose a simple diagnostic approach to guide metabolic investigations based on the clinical course of symptoms, the type of abnormal movements, and brain MRI abnormalities.

Advances in lafora progressive myoclonus epilepsy

Abstract Lafora progressive myoclonus epilepsy is an autosomal recessive, fatal, generalized polyglucosan storage disorder that occurs in childhood or adolescence with stimulus sensitive epilepsy (resting and action myoclonias, grand mal, and absence), dementia, ataxia and rapid neurologic deterioration. Mutations in EPM2A/laforin cause 58% of cases and mutations in EPM2B/malin cause 35% of cases. Accumulating evidence points to Lafora disease as primarily a disorder of cell death with impaired clearance of misfolded proteins, as shown by ubiquitin-positive aggresomes in HeLa cells transfected with mutated laforin, ubiquitin-positive polyglucosan inclusion bodies, and malin/E3 ubiquitin ligase polyubiquitination of laforin. How polyglucosan inclusion bodies accumulate is still a mystery. Polyglucosan accumulates hypothetically because of an overactive polyglucosan biosynthetic pathway or a breakdown in polyglucosan degradation. Five separate laboratories are looking for the biochemical pathways that connect laforin and malin to polyglucosan synthesis or degradation. A curative therapy for human Lafora disease with laforin replacement therapy using neutral pegylated immunoliposomes is being investigated.

Null mutations and lethal congenital form of glycogen storage disease type IV

Glycogen branching enzyme deficiency (glycogen storage disease type IV, GSD-IV) is a rare autosomal recessive disorder of the glycogen synthesis with high mortality. Two female newborns showed severe hypotonia at birth and both died of cardiorespiratory failure, at 4 and 12 weeks, respectively. In both patients, muscle biopsies showed deposits of PAS-positive diastase-resistant material and biochemical analysis in cultured fibroblasts showed markedly reduced glycogen branching enzyme activity. Direct sequencing of GBE1 gene revealed that patient 1 was homozygous for a novel c.691+5 g>c in intron 5 (IVS5+5 g>c). RT-PCR analysis of GBE1 transcripts from fibroblasts cDNA showed that this mutation produce aberrant splicing. Patient 2 was homozygous for a novel c.1643G>A mutation leading to a stop at codon 548 in exon 13 (p.W548X). These data underscore that in GSD-IV a severe phenotype correlates with null mutations, and indicate that RNA analysis is necessary to characterize functional consequences of intronic mutations.

Polyglucosan body disease myopathy: An unusual presentation

Polyglucosan body disease (PBD) is a slowly progressive adult-onset glycogen storage disorder that typically affects upper and lower neurons. Myopathy, as a complication of PBD has been reported rarely and clinically manifests as chronic limb-girdle muscle weakness. We report an unusual case of PBD myopathy presenting as an asymmetric motor syndrome that clinically overlapped with amyotrophic lateral sclerosis, further expanding the phenotype of this disorder.

Leukodystrophies: clinical and genetic aspects

The leukodystrophies comprise an ever-expanding group of rare central nervous system disorders with defined clinical, pathological, and genetic characteristics. The broader term, leukoencephalopathy, is applied to all brain white matter diseases, whether their molecular cause is known. Magnetic resonance imaging has helped to elucidate new forms of leukodystrophy as well as to permit longitudinal studies of disease progression. The white matter abnormality may appear similar in different forms of leukodystrophy so that in most cases, further studies such as magnetic resonance spectroscopy, tissue biopsies, enzyme studies, and molecular DNA analyses are needed to pinpoint the specific diagnosis. The primary inherited leukoencephalopathies include dysmyelinating, hypomyelinative, and vacuolating forms. Metabolic and vascular causes account for most of the secondary forms, but other inherited syndromes are recognized that have their onset in childhood or adult life and are characterized by distinctive clinical and neuropathologic features. This review discusses some of the mechanisms that have been proposed to explain deficiencies of myelin and the molecular genetic bases underlying these disorders.

Glycogen storage disease: clinical, biochemical, and molecular heterogeneity

Glycogen storage diseases (GSDs) are characterized by abnormal inherited glycogen metabolism in the liver, muscle, and brain and divided into types 0 to X. GSD type I, glucose 6-phosphatase system, has types Ia, Ib, Ic, and Id, glucose 6-phosphatase, glucose 6-phosphate translocase, pyrophosphate translocase, and glucose translocase deficiencies, respectively. GSD type II is caused by defective lysosomal alpha-glucosidase (GAA), subdivided into 4 onset forms. GSD type III, amylo-1,6-glucosidase deficiency, is subdivided into 6 forms. GSD type IV, Andersen disease or amylopectinosis, is caused by deficiency of the glycogen-branching enzyme in numerous forms. GSD type V, McArdle disease or muscle phosphorylase deficiency, is divided into 2 forms. GSD type VI is characterized by liver phosphorylase deficiency. GSD type VII, phosphofructokinase deficiency, has 2 subtypes. GSD types VIa, VIII, IX, or X are supposedly caused by tissue-specific phosphorylase kinase deficiency. GSD type 0, glycogen synthase deficiency, is divided into 2 subtypes.

Neuropathology of Charcot-Marie-Tooth and related disorders

The peripheral nervous system (PNS), with all its branches and connections, is so complex that it is impossible to study all components at the light or electron microscopic level in any individual case; nevertheless, in certain diseases a simple nerve biopsy may suffice to arrive at a precise diagnosis. Structural changes of the PNS in neuropathies of the Charcot-Marie-Tooth (CMT) type and related disorders comprise various components of the PNS. These include peripheral motor, sensory, and autonomous neurons with their axons, Schwann cells, and myelin sheaths in the radicular and peripheral nerves as well as satellite cells in spinal and autonomous ganglia. Astrocytes, oligodendroglial cells, and microglial cells around motor neurons in the anterior horn and around sensory neurons in other areas of the spinal cord are also involved. In addition, connective tissue elements such as endoneurial, perineurial, and epineurial components including blood and lymph vessels play an important role. This review focuses on the cellular components and organelles involved, that is, myelin sheaths, axons with their micro-tubules and neurofilaments; nuclei, mitochondria, endoplasmic reticulum, and connective tissue including the perineurium and blood vessels. A major role is attributed to recent progress in the pathomorphology of various types of CMT1, 2,4, CMTX, and HMNSL, based on light and electron microscopic findings, morphometry, teased fiber studies, and new immunohisto-chemical results such as staining of certain periaxin domains in CMT4F.

Prenatal diagnosis of glycogen storage disease type IV

BACKGROUND

Glycogen storage disease type IV (GSD-IV) is a rare autosomal recessive disorder due to mutations in the GBE1 gene causing deficiency of the glycogen branching enzyme (GBE). Prenatal diagnosis has occasionally been performed by the measurement of the GBE activity in cultured chorionic villi (CV) cells.

METHODS

Two unrelated probands with severe hypotonia at birth and death during the neonatal period were diagnosed with GSD-IV on the basis of postmortem histological findings. DNA analysis revealed truncating GBE1 mutations in both families.

RESULTS

Prenatal diagnosis was performed in subsequent pregnancies by determination of branching enzyme activity and DNA analysis of CV or cultured amniocytes. Detailed autopsies of the affected fetuses at 14 and 24 weeks of gestation demonstrated intracellular inclusions of abnormal glycogen characteristic of GSD-IV.

CONCLUSION

Prenatal diagnosis of GSD-IV by DNA analysis is highly accurate in genetically confirmed cases.

Cognitive impairment in neuromuscular disorders

Several studies have suggested the presence of central nervous system involvement manifesting as cognitive impairment in diseases traditionally confined to the peripheral nervous system. The aim of this review is to highlight the character of clinical, genetic, neurofunctional, cognitive, and psychiatric deficits in neuromuscular disorders. A high correlation between cognitive features and cerebral protein expression or function is evident in Duchenne muscular dystrophy, myotonic dystrophy (Steinert disease), and mitochondrial encephalomyopathies; direct correlation between tissue-specific protein expression and cognitive deficits is still elusive in certain neuromuscular disorders presenting with or without a cerebral abnormality, such as congenital muscular dystrophies, congenital myopathies, amyotrophic lateral sclerosis, adult polyglucosan body disease, and limb-girdle muscular dystrophies. No clear cognitive deficits have been found in spinal muscular atrophy and facioscapulohumeral dystrophy.

Fatal congenital heart glycogenosis caused by a recurrent activating R531Q mutation in the gamma 2-subunit of AMP-activated protein kinase (PRKAG2), not by phosphorylase kinase deficiency

Fatal congenital nonlysosomal cardiac glycogenosis has been attributed to a subtype of phosphorylase kinase deficiency, but the underlying genes and mutations have not been identified. Analyzing four sporadic, unrelated patients, we found no mutations either in the eight genes encoding phosphorylase kinase subunits or in the two genes encoding the muscle and brain isoforms of glycogen phosphorylase. However, in three of five patients, we identified identical heterozygous R531Q missense mutations of the PRKAG2 gene, which encodes the gamma 2-subunit of AMP-activated protein kinase, a key regulator of energy balance. Biochemical characterization of the recombinant R531Q mutant protein showed >100-fold reduction of binding affinities for the regulatory nucleotides AMP and ATP but an enhanced basal activity and increased phosphorylation of the alpha -subunit. Other PRKAG2 missense mutations were previously identified in patients with autosomal dominant hypertrophic cardiomyopathy with Wolff-Parkinson-White syndrome, characterized by juvenile-to-adult clinical onset, moderate cardiac glycogenosis, disturbed excitation conduction, risk of sudden cardiac death in midlife, and molecular perturbations that are similar to--but less severe than--those observed for the R531Q mutation. Thus, recurrent heterozygous R531Q missense mutations in PRKAG2 give rise to a massive nonlysosomal cardiac glycogenosis of fetal symptomatic onset and rapidly fatal course, constituting a genotypically and clinically distinct variant of hypertrophic cardiomyopathy with Wolff-Parkinson-White syndrome. R531Q and other PRKAG2 mutations enhance the basal activity and alpha -subunit phosphorylation of AMP-activated protein kinase, explaining the dominant nature of PRKAG2 disease mutations. Since not all cases displayed PRKAG2 mutations, fatal congenital nonlysosomal cardiac glycogenosis seems to be genetically heterogeneous. However, the existence of a heart-specific primary phosphorylase kinase deficiency is questionable, because no phosphorylase kinase mutations were found.

Arthrogryposis multiplex with deafness, inguinal hernias, and early death: A family report of a probably autosomal recessive trait

We report on three male newborn infants of a highly inbred Lebanese family presenting with a characteristic phenotype: arthrogryposis multiplex, deafness, large inguinal hernia, hiccup-like diaphragmatic contractions, and inability to suck, requiring nasogastric gavage feeding. All three boys died from respiratory failure during the first 3 months of life. Intra vitam or post mortem examinations revealed myopathic changes and elevated glycogen content of muscle tissue. This new syndrome is probably transmitted in an autosomal recessive mode, although X-linked inheritance cannot be excluded.

Adult polyglucosan body disease: A case report of a manifesting heterozygote

A 62-year-old man developed progressive gait instability, bladder dysfunction, proximal weakness, distal sensory loss, and mild cognitive impairment over 6 years. Neurologic examination revealed upper and lower motor neuron dysfunction in the lower extremities, with distal sensory loss. Electrodiagnostic studies, magnetic resonance imaging of the brain, and sural nerve biopsy were consistent with adult polyglucosan body disease. Biochemical and genetic analyses demonstrated reduced glycogen brancher enzyme levels associated with a heterozygous point mutation (Tyr329Ser or Y329S) in the glycogen brancher enzyme gene on chromosome 3. Mutational heterozygosity in the glycogen brancher enzyme gene has not been previously reported as a cause for this rare disease. A review of the clinical presentation, pathogenesis, etiology, and diagnosis of this disease is presented.

Neonatal type IV glycogen storage disease associated with "null" mutations in glycogen branching enzyme 1

The fatal neonatal form of type IV glycogen storage disease (GSD IV) was diagnosed on light and electron microscopy and by analysis of GBE1 , the gene encoding glycogen branching enzyme. We report two novel truncating mutations, as well as the first genomic mutational analysis of GBE1 using denaturing high performance liquid chromatography.

Atypical parkinsonism combining α‐synuclein inclusions and polyglucosan body disease

Adult polyglucosan body disease (APGBD) is a rare disorder affecting the central and peripheral nervous systems and in which parkinsonism is unusual. A 71-year-old man presented levodopa-unresponsive parkinsonism with urinary incontinence and recurrent syncopes of 6 years standing masquerading as atypical parkinsonism of the multiple system atrophy (MSA-P) type. Brain histopathology demonstrated massive accumulation of polyglucosan bodies particularly in the putamen. In addition, there were dense alpha-synuclein-positive cytoplasmic oligodendroglial inclusions in the pons and in the middle cerebellar peduncle. These inclusions may be either due to the chance association of MSA-P with APGBD, or pathologically related to APGBD.

Severe neonatal onset of glycogenosis type IV: clinical and laboratory findings leading to diagnosis in two siblings

Glycogenosis type IV is an autosomal recessive disease, exceptionally diagnosed at birth: only very few reports of the fatal perinatal neuromuscular form have been described. We report on two sibling male newborns who died at 10 and 4 weeks of age with clinical signs of a systemic storage disease. Prenatal history included polyhydramnios, reduced fetal movements and fetal hydrops, and Caesarean section was performed at 36 weeks of gestational age because of fetal distress. At birth, both babies showed severe hypotonia, hyporeflexia and no spontaneous breathing activity. They never showed active movements, sucking and swallowing and were respirator-dependent until death. A muscle biopsy revealed, in both patients, the presence of PAS-positive and partially diastase-resistant cytoplasmic inclusions containing granular and filamentous amylopectin-like material. This suggested that the stored material consisted of abnormal glycogen. At autopsy, ultrastructural examination of cardiac and skeletal muscle, liver, kidney and brain showed PAS-positive diastase-resistant eosinophilic cytoplasmic inclusions. Determination of branching enzyme activity, in cultured fibroblasts from the second patient, showed markedly reduced enzyme activity, confirming diagnosis of glycogenosis type IV. Our patients showed the full spectrum of both prenatal signs (hydrops, polyhydramnios) and postnatal signs (hypotonia, hyporeflexia, absence of active movements, cardiomegaly), which have been reported previously. They suffered from a very severe form of glycogenosis type IV with clinical and histological involvement of many tissues and organs. Diagnosis was accomplished on the second baby and required several biochemical and histological studies, in order to rule out both neuromuscular disorders and the most common storage diseases with neonatal onset. In our experience, the correct interpretation of the histological findings was essential in the search for the diagnosis.

Adult polyglucosan body disease: Case description of an expanding genetic and clinical syndrome

A non-Jewish patient is described who had adult polyglucosan body disease (APBD) and glycogen branching enzyme (GBE) deficiency without GBE mutation. A heterozygous polymorphism (Val160Ile) was found, and also discovered in 1 of 50 normal individuals. Magnetic resonance imaging demonstrated increased T2 signal in the midbrain, medullary olives, dentate nuclei, cerebellar peduncles, and internal and external capsules, with vermian atrophy. Both muscle and nerve biopsy revealed perivascular inflammatory infiltrates. These findings expand the clinical and genetic spectrum of APBD. Factors other than mutation of the expressed GBE gene may cause enzyme deficiency and varied expression and development of APBD.

Muscle glycogenosis with low phosphorylase kinase activity: mutations in PHKA1, PHKG1 or six other candidate genes explain only a minority of cases

Muscle-specific deficiency of phosphorylase kinase (Phk) causes glycogen storage disease, clinically manifesting in exercise intolerance with early fatiguability, pain, cramps and occasionally myoglobinuria. In two patients and in a mouse mutant with muscle Phk deficiency, mutations were previously found in the muscle isoform of the Phk alpha subunit, encoded by the X-chromosomal PHKA1 gene (MIM # 311870). No mutations have been identified in the muscle isoform of the Phk gamma subunit (PHKG1). In the present study, we determined Q1the structure of the PHKG1 gene and characterized its relationship to several pseudogenes. In six patients with adult- or juvenile-onset muscle glycogenosis and low Phk activity, we then searched for mutations in eight candidate genes. The coding sequences of all six genes that contribute to Phk in muscle were analysed: PHKA1, PHKB, PHKG1, CALM1, CALM2 and CALM3. We also analysed the genes of the muscle isoform of glycogen phosphorylase (PYGM), of a muscle-specific regulatory subunit of the AMP-dependent protein kinase (PRKAG3), and the promoter regions of PHKA1, PHKB and PHKG1. Only in one male patient did we find a PHKA1 missense mutation (D299V) that explains the enzyme deficiency. Two patients were heterozygous for single amino-acid replacements in PHKB that are of unclear significance (Q657K and Y770C). No sequence abnormalities were found in the other three patients. If these results can be generalized, only a fraction of cases with muscle glycogenosis and a biochemical diagnosis of low Phk activity are caused by coding, splice-site or promoter mutations in PHKA1, PHKG1 or other Phk subunit genes. Most patients with this diagnosis probably are affected either by elusive mutations of Phk subunit genes or by defects in other, unidentified genes.

Carbon export from arbuscular mycorrhizal roots involves the translocation of carbohydrate as well as lipid

Arbuscular mycorrhizal (AM) fungi take up photosynthetically fixed carbon from plant roots and translocate it to their external mycelium. Previous experiments have shown that fungal lipid synthesized from carbohydrate in the root is one form of exported carbon. In this study, an analysis of the labeling in storage and structural carbohydrates after (13)C(1) glucose was provided to AM roots shows that this is not the only pathway for the flow of carbon from the intraradical to the extraradical mycelium (ERM). Labeling patterns in glycogen, chitin, and trehalose during the development of the symbiosis are consistent with a significant flux of exported glycogen. The identification, among expressed genes, of putative sequences for glycogen synthase, glycogen branching enzyme, chitin synthase, and for the first enzyme in chitin synthesis (glutamine fructose-6-phosphate aminotransferase) is reported. The results of quantifying glycogen synthase gene expression within mycorrhizal roots, germinating spores, and ERM are consistent with labeling observations using (13)C-labeled acetate and glycerol, both of which indicate that glycogen is synthesized by the fungus in germinating spores and during symbiosis. Implications of the labeling analyses and gene sequences for the regulation of carbohydrate metabolism are discussed, and a 4-fold role for glycogen in the AM symbiosis is proposed: sequestration of hexose taken from the host, long-term storage in spores, translocation from intraradical mycelium to ERM, and buffering of intracellular hexose levels throughout the life cycle.

Lafora's disease: towards a clinical, pathologic, and molecular synthesis

Lafora's disease is one of five inherited progressive myoclonus epilepsy syndromes. It is an autosomal-recessive disorder with onset in late childhood or adolescence. Characteristic seizures include myoclonic and occipital lobe seizures with visual hallucinations, scotomata, and photoconvulsions. The course of the disease consists of worsening seizures and an inexorable decline in mental and other neurologic functions that result in dementia and death within 10 years of onset. Pathology reveals pathognomonic polyglucosan inclusions that are not seen in any other progressive myoclonus epilepsy. Lafora's disease is one of several neurologic conditions associated with brain polyglucosan bodies. Why Lafora's polyglucosan bodies alone are associated with epilepsy is unknown and is discussed in this article. Up to 80% of patients with Lafora's disease have mutations in the EPM2A gene. Although common mutations are rare, simple genetic tests to identify most mutations have been established. At least one other still-unknown gene causes Lafora's disease. The EPM2A gene codes for the protein laforin, which localizes at the plasma membrane and the rough endoplasmic reticulum and functions as a dual-specificity phosphatase. Work toward establishing the connection between laforin and Lafora's disease polyglucosans is underway, as are attempts to replace it into the central nervous system of patients with Lafora's disease.

Adult polyglucosan body disease

We describe a case of adult polyglucosan body disease with characteristic clinical symptoms of peripheral neuropathy, upper motor neuron signs, and bowel and bladder dysfunction. Sural nerve biopsy revealed diagnostic intra-axonal polyglucosan bodies. On electron microscopic examination, the inclusions were located mainly within myelinated nerve fibers and consisted of branched filaments that were 6 to 8 nm wide. The diagnosis of adult polyglucosan body disease was confirmed by a skin biopsy from the axilla showing similar inclusions in myoepithelial cells of apocrine glands. This report provides additional evidence that skin biopsy, to date advocated by a single case report only, may be a less invasive and simpler diagnostic alternative to sural nerve or brain biopsies.