Immunodeficiency, autoinflammation and amylopectinosis in humans with inherited HOIL-1 and LUBAC deficiency.

We report the clinical description and molecular dissection of a new fatal human inherited disorder characterized by chronic autoinflammation, invasive bacterial infections and muscular amylopectinosis. Patients from two kindreds carried biallelic loss-of-expression and loss-of-function mutations in HOIL1 (RBCK1), a component of the linear ubiquitination chain assembly complex (LUBAC). These mutations resulted in impairment of LUBAC stability. NF-κB activation in response to interleukin 1ß (IL-1ß) was compromised in the patients' fibroblasts. By contrast, the patients' mononuclear leukocytes, particularly monocytes, were hyper-responsive to IL-1ß. The consequences of human HOIL-1 and LUBAC deficiencies for IL-1ß responses thus differed between cell types, consistent with the unique association of autoinflammation and immunodeficiency in these patients. These data suggest that LUBAC regulates NF-κB-dependent IL-1ß responses differently in different cell types.

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.

Unraveling a history of overlap: A phenotypic comparison of RBCK1-related disease and glycogen storage disease type IV.

RBCK1-related disease is a rare, multisystemic disorder for which our current understanding of the natural history is limited. A number of individuals initially carried clinical diagnoses of glycogen storage disease IV (GSD IV), but were later found to harbor RBCK1 pathogenic variants, demonstrating challenges of correctly diagnosing RBCK1-related disease. This study carried out a phenotypic comparison between RBCK1-related disease and GSD IV to identify features that clinically differentiate these diagnoses. Literature review and retrospective chart review identified 25 individuals with RBCK1-related disease and 36 with the neuromuscular subtype of GSD IV. Clinical features were evaluated to assess for statistically significant differences between the conditions. At a system level, any cardiac, autoinflammation, immunodeficiency, growth, or dermatologic involvement were suggestive of RBCK1, whereas any respiratory involvement suggested GSD IV. Several features warrant further exploration as predictors of RBCK1, such as generalized weakness, heart transplant, and recurrent infections, among others. Distinguishing RBCK1-related disease will facilitate correct diagnoses and pave the way for accurately identifying affected individuals, as well as for developing management recommendations, treatment, and an enhanced understanding of the natural history. This knowledge may also inform which individuals thought to have GSD IV should undergo reevaluation for RBCK1.

Severe neuromuscular forms of glycogen storage disease type IV: Histological, clinical, biochemical, and molecular findings in a large French case series.

Glycogen storage disease type IV (GSD IV), also called Andersen disease, or amylopectinosis, is a highly heterogeneous autosomal recessive disorder caused by a glycogen branching enzyme (GBE, 1,4-alpha-glucan branching enzyme) deficiency secondary to pathogenic variants on GBE1 gene. The incidence is evaluated to 1:600 000 to 1:800 000 of live births. GBE deficiency leads to an excessive deposition of structurally abnormal, amylopectin-like glycogen in affected tissues (liver, skeletal muscle, heart, nervous system, etc.). Diagnosis is often guided by histological findings and confirmed by GBE activity deficiency and molecular studies. Severe neuromuscular forms of GSD IV are very rare and of disastrous prognosis. Identification and characterization of these forms are important for genetic counseling for further pregnancies. Here we describe clinical, histological, enzymatic, and molecular findings of 10 cases from 8 families, the largest case series reported so far, of severe neuromuscular forms of GSD IV along with a literature review. Main antenatal features are: fetal akinesia deformation sequence or arthrogryposis/joint contractures often associated with muscle atrophy, decreased fetal movement, cystic hygroma, and/or hydrops fetalis. If pregnancy is carried to term, the main clinical features observed at birth are severe hypotonia and/or muscle atrophy, with the need for mechanical ventilation, cardiomyopathy, retrognathism, and arthrogryposis. All our patients were stillborn or died within 1 month of life. In addition, we identified five novel GBE1 variants.

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.

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.

[Infant glycogen storage disease type â £: a clinicopathological and genetic characteristics analysis of five cases].

Objective: To investigate the clinical pathology and gene mutation characteristics of patients with glycogen storage disease type Ⅳ (GSD Ⅳ). Methods: The clinical data, liver histopathology and ultrastructural morphology, and gene sequencing results of 5 GSD Ⅳ cases diagnosed in the Children's Hospital Affiliated to Shanghai Jiaotong University School of Medicine and the Children's Hospital of Fudan University from January 2015 to February 2022 were collected and analyzed retrospectively. Results: Among the 5 cases, 3 were male and 2 were female, ranging in age from 4 months to 1 year and 9 months. The clinical manifestations included fever, hepatosplenomegaly, liver insufficiency, growth retardation and hypotonia. Four cases had liver biopsy showing ground-glass-like changes in hepatocytes with intracytoplasmic inclusion bodies and varying degrees of fibrosis. Liver electron microscopy in 2 cases showed that the level of glycogen increased to varying degrees, and the cytoplasm was filled with low electron density substances. Genetic testing revealed that 3 cases had compound heterozygous variants in GBE1 gene; 1 case had a single pathogenic variant in GBE1 gene; and 1 case was deceased with no genetic testing, but each parent was tested for a heterozygous variant in the GBE1 gene. A total of 9 GBE1 gene mutations were detected, 3 of which were reported mutations and 6 novel mutations. One case died of liver cirrhosis, and 1 case underwent autologous liver transplantation. After transplantation, the liver function basically returned to normal, and the growth and development improved; the other 3 cases were managed through diet control and symptomatic treatment. Conclusions: CSD Ⅳ is an extremely rare inherited metabolic disease caused by GBE1 gene mutation, often presenting with hepatic and neuromuscular disorders, with heterogeneous clinical manifestations. The diagnosis mainly depends on histopathology and a pedigree gene analysis.

The potential of dietary treatment in patients with glycogen storage disease type IV.

There is paucity of literature on dietary treatment in glycogen storage disease (GSD) type IV and formal guidelines are not available. Traditionally, liver transplantation was considered the only treatment option for GSD IV. In light of the success of dietary treatment for the other hepatic forms of GSD, we have initiated this observational study to assess the outcomes of medical diets, which limit the accumulation of glycogen. Clinical, dietary, laboratory, and imaging data for 15 GSD IV patients from three centres are presented. Medical diets may have the potential to delay or prevent liver transplantation, improve growth and normalize serum aminotransferases. Individual care plans aim to avoid both hyperglycaemia, hypoglycaemia and/or hyperketosis, to minimize glycogen accumulation and catabolism, respectively. Multidisciplinary monitoring includes balancing between traditional markers of metabolic control (ie, growth, liver size, serum aminotransferases, glucose homeostasis, lactate, and ketones), liver function (ie, synthesis, bile flow and detoxification of protein), and symptoms and signs of portal hypertension.

Hallmarks of oxidative stress in the livers of aged mice with mild glycogen branching enzyme deficiency.

Glycogen branching enzyme (GBE1) introduces branching points in the glycogen molecule during its synthesis. Pathogenic GBE1 gene mutations lead to glycogen storage disease type IV (GSD IV), which is characterized by excessive intracellular accumulation of abnormal, poorly branched glycogen in affected tissues and organs, mostly in the liver. Using heterozygous Gbe1 knock-out mice (Gbe1+/-), we analyzed the effects of moderate GBE1 deficiency on oxidative stress in the liver. The livers of aged Gbe1+/- mice (22 months old) had decreased GBE1 protein levels, which caused a mild decrease in the degree of glycogen branching, but did not affect the tissue glycogen content. GBE1 deficiency was accompanied by increased protein carbonylation and elevated oxidation of the glutathione pool, indicating the existence of oxidative stress. Furthermore, we have observed increased levels of glutathione peroxidase and decreased activity of respiratory complex I in Gbe1+/- livers. Our data indicate that even mild changes in the degree of glycogen branching, which did not lead to excessive glycogen accumulation, may have broader effects on cellular bioenergetics and redox homeostasis. In young animals cellular homeostatic mechanisms are able to counteract those changes, while in aged tissues the changes may lead to increased oxidative stress.

Glycogen Storage Disease Type IV Diagnosed at Fetal Autopsy.

Glycogen storage disease type IV (GSD IV; Andersen's disease) is a rare autosomal recessive disorder that results from defects in the GBE1 gene (3p12.2) and subsequent deficiencies of glycogen branching. We report a case of GSD IV diagnosed at autopsy in a 35 4/7 weeks gestational age female neonate that died shortly after birth. Multisystem blue, ground glass inclusions initially presumed artefactual were periodic acid-Schiff positive, diastase resistant. Chromosomal microarray analysis identified a deletion of exons 2 through 16 of the GBE1 gene and whole exome sequencing identified a nonsense mutation within exon 14, confirming the diagnosis of GSD IV. A strong index of suspicion was required determine GSD IV as the ultimate cause of death, illustrating the need for critical evaluation of postmortem artifact in the setting of fetal demise of unknown etiology and highlighting the role of postmortem molecular diagnostics in a subset of cases.

The inward rectifier potassium channel Kir2.1 is required for osteoblastogenesis.

Andersen's syndrome (AS) is a rare and dominantly inherited pathology, linked to the inwardly rectifying potassium channel Kir2.1. AS patients exhibit a triad of symptoms that include periodic paralysis, cardiac dysrhythmia and bone malformations. Some progress has been made in understanding the contribution of the Kir2.1 channel to skeletal and cardiac muscle dysfunctions, but its role in bone morphogenesis remains unclear. We isolated myoblast precursors from muscle biopsies of healthy individuals and typical AS patients with dysmorphic features. Myoblast cultures underwent osteogenic differentiation that led to extracellular matrix mineralization. Osteoblastogenesis was monitored through the activity of alkaline phosphatase, and through the hydroxyapatite formation using Alizarin Red and Von Kossa staining techniques. Patch-clamp recordings revealed the presence of an inwardly rectifying current in healthy cells that was absent in AS osteoblasts, showing the dominant-negative effect of the Kir2.1 mutant allele in osteoblasts. We also found that while control cells actively synthesize hydroxyapatite, AS osteoblasts are unable to efficiently form any extracellular matrix. To further demonstrate the role of the Kir2.1 channels during the osteogenesis, we inhibited Kir2.1 channel activity in healthy patient cells by applying extracellular Ba(2+) or using adenoviruses carrying mutant Kir2.1 channels. In both cases, cells were no longer able to produce extracellular matrixes. Moreover, osteogenic activity of AS osteoblasts was restored by rescue experiments, via wild-type Kir2.1 channel overexpression. These observations provide a proof that normal Kir2.1 channel function is essential during osteoblastogenesis.

A novel mouse model that recapitulates adult-onset glycogenosis type 4.

Glycogen storage disease type IV (GSD IV) is a rare autosomal recessive disorder caused by deficiency of the glycogen-branching enzyme (GBE). The diagnostic hallmark of the disease is the accumulation of a poorly branched form of glycogen known as polyglucosan (PG). The disease is clinically heterogeneous, with variable tissue involvement and age at onset. Complete loss of enzyme activity is lethal in utero or in infancy and affects primarily the muscle and the liver. However, residual enzyme activity as low as 5-20% leads to juvenile or adult onset of a disorder that primarily affects the central and peripheral nervous system and muscles and in the latter is termed adult polyglucosan body disease (APBD). Here, we describe a mouse model of GSD IV that reflects this spectrum of disease. Homologous recombination was used to knock in the most common GBE1 mutation p.Y329S c.986A > C found in APBD patients of Ashkenazi Jewish decent. Mice homozygous for this allele (Gbe1(ys/ys)) exhibit a phenotype similar to APBD, with widespread accumulation of PG. Adult mice exhibit progressive neuromuscular dysfunction and die prematurely. While the onset of symptoms is limited to adult mice, PG accumulates in tissues of newborn mice but is initially absent from the cerebral cortex and heart muscle. Thus, PG is well tolerated in most tissues, but the eventual accumulation in neurons and their axons causes neuropathy that leads to hind limb spasticity and premature death. This mouse model mimics the pathology and pathophysiologic features of human adult-onset branching enzyme deficiency.

Structural basis of glycogen branching enzyme deficiency and pharmacologic rescue by rational peptide design.

Glycogen branching enzyme 1 (GBE1) plays an essential role in glycogen biosynthesis by generating α-1,6-glucosidic branches from α-1,4-linked glucose chains, to increase solubility of the glycogen polymer. Mutations in the GBE1 gene lead to the heterogeneous early-onset glycogen storage disorder type IV (GSDIV) or the late-onset adult polyglucosan body disease (APBD). To better understand this essential enzyme, we crystallized human GBE1 in the apo form, and in complex with a tetra- or hepta-saccharide. The GBE1 structure reveals a conserved amylase core that houses the active centre for the branching reaction and harbours almost all GSDIV and APBD mutations. A non-catalytic binding cleft, proximal to the site of the common APBD mutation p.Y329S, was found to bind the tetra- and hepta-saccharides and may represent a higher-affinity site employed to anchor the complex glycogen substrate for the branching reaction. Expression of recombinant GBE1-p.Y329S resulted in drastically reduced protein yield and solubility compared with wild type, suggesting this disease allele causes protein misfolding and may be amenable to small molecule stabilization. To explore this, we generated a structural model of GBE1-p.Y329S and designed peptides ab initio to stabilize the mutation. As proof-of-principle, we evaluated treatment of one tetra-peptide, Leu-Thr-Lys-Glu, in APBD patient cells. We demonstrate intracellular transport of this peptide, its binding and stabilization of GBE1-p.Y329S, and 2-fold increased mutant enzymatic activity compared with untreated patient cells. Together, our data provide the rationale and starting point for the screening of small molecule chaperones, which could become novel therapies for this disease.

Glycogen Storage Disease Type IV: A Case With Histopathologic Findings in First-Trimester Placental Tissue.

A 30-yr-old woman presented with 2 consecutive miscarriages within 7 mo. Histopathologic examination of the placental tissue showed intracytoplasmic inclusion vacuoles with a strong reaction in Periodic acid-Schiff staining and a slightly pallor reaction in alcian blue staining. Additional molecular genetic analyses confirmed glycogen storage disease Type IV with the finding of compound heterozygosity for 2 mutations (c.691+2T>C and c.1570C>T, p.R524X) in the GBE1 gene. We conclude that glycogen storage disease Type IV can cause early miscarriage and that diagnosis can initially be made on histopathologic examination. Genetic analysis is required to confirm the diagnosis and to offer prenatal genetic testing in future pregnancies.

Exome sequencing positively identified relevant alterations in more than half of cases with an indication of prenatal ultrasound anomalies.

OBJECTIVE: Exome sequencing is a successful option for diagnosing individuals with previously uncharacterized genetic conditions, however little has been reported regarding its utility in a prenatal setting. The goal of this study is to describe the results from a cohort of fetuses for which exome sequencing was performed. METHODS: We performed a retrospective analysis of the first seven cases referred to our laboratory for exome sequencing following fetal demise or termination of pregnancy. All seven pregnancies had multiple congenital anomalies identified by level II ultrasound. Exome sequencing was performed on trios using cultured amniocytes or products of conception from the affected fetuses. RESULTS: Relevant alterations were identified in more than half of the cases (4/7). Three of the four were categorized as 'positive' results, and one of the four was categorized as a 'likely positive' result. The provided diagnoses included osteogenesis imperfecta II (COL1A2), glycogen storage disease IV (GBE1), oral-facial-digital syndrome 1 (OFD1), and RAPSN-associated fetal akinesia deformation sequence. CONCLUSION: This data suggests that exome sequencing is likely to be a valuable diagnostic testing option for pregnancies with multiple congenital anomalies detected by prenatal ultrasound; however, additional studies with larger cohorts of affected pregnancies are necessary to confirm these findings.

Glycogen Storage Disorder due to Glycogen Branching Enzyme (GBE) Deficiency: A Diagnostic Dilemma.

Glycogen branching enzyme deficiency/Andersen disease can manifest with a spectrum of clinical phenotypes, making the diagnosis difficult. An 11-year-old Pakistani boy presented with a history of progressive weakness and delayed milestones. Echocardiography showed features of dilated cardiomyopathy. He was suspected to have congenital myopathy and was evaluated further. Muscle biopsy showed subsarcolemmal accumulation of basophilic material, which stained positively with Periodic acid-Schiff reagent (diastase-resistant). Ultrastructural examination revealed accumulation of structurally abnormal forms of filamentous glycogen, confirming the diagnosis as Andersen disease. As histopathological and immunohistochemical evaluation of muscle biopsies is not always diagnostic, ultrastructural examination may serve as a valuable adjunct in difficult cases.

Natural history study of hepatic glycogen storage disease type IV and comparison to Gbe1ys/ys model.

BackgroundGlycogen storage disease type IV (GSD IV) is an ultrarare autosomal recessive disorder that causes deficiency of functional glycogen branching enzyme and formation of abnormally structured glycogen termed polyglucosan. GSD IV has traditionally been categorized based on primary hepatic or neuromuscular involvement, with hepatic GSD IV subclassified as discrete subtypes: classic (progressive) and nonprogressive.MethodsTo better understand the progression of liver disease in GSD IV, we present clinical and histopathology data from 23 patients from around the world and characterized the liver involvement in the Gbe1ys/ys knockin mouse model.ResultsWe propose an alternative to the established subtype-based terminology for characterizing liver disease in GSD IV and recognize 3 tiers of disease severity: (i) "severe progressive" liver disease, (ii) "intermediate progressive" liver disease, and (iii) "attenuated" liver disease. Analysis of liver pathology revealed that risk for liver failure cannot be predicted from liver biopsy findings alone in individuals affected by GSD IV. Moreover, analysis of postmortem liver pathology from an individual who died over 40 years after being diagnosed with nonprogressive hepatic GSD IV in childhood verified that liver fibrosis did not regress. Last, characterization of the liver involvement in a mouse model known to recapitulate the adult-onset neurodegenerative form of GSD IV (Gbe1ys/ys mouse model) demonstrated hepatic disease.ConclusionOur findings challenge the established subtype-based view of GSD IV and suggest that liver disease severity among patients with GSD IV represents a disease continuum.Trial registrationClinicalTrials.gov NCT02683512FundingNone.

Generation of a novel mouse model that recapitulates early and adult onset glycogenosis type IV.

Glycogen storage disease type IV (GSD IV) is a rare autosomal recessive disorder caused by deficiency of the glycogen branching enzyme (GBE). The diagnostic feature of the disease is the accumulation of a poorly branched form of glycogen known as polyglucosan (PG). The disease is clinically heterogeneous, with variable tissue involvement and age of disease onset. Absence of enzyme activity is lethal in utero or in infancy affecting primarily muscle and liver. However, residual enzyme activity (5-20%) leads to juvenile or adult onset of a disorder that primarily affects muscle as well as central and peripheral nervous system. Here, we describe two mouse models of GSD IV that reflect this spectrum of disease. Homologous recombination was used to insert flippase recognition target recombination sites around exon 7 of the Gbe1 gene and a phosphoglycerate kinase-Neomycin cassette within intron 7, leading to a reduced synthesis of GBE. Mice bearing this mutation (Gbe1(neo/neo)) exhibit a phenotype similar to juvenile onset GSD IV, with wide spread accumulation of PG. Meanwhile, FLPe-mediated homozygous deletion of exon 7 completely eliminated GBE activity (Gbe1(-/-)), leading to a phenotype of lethal early onset GSD IV, with significant in utero accumulation of PG. Adult mice with residual GBE exhibit progressive neuromuscular dysfunction and die prematurely. Differently from muscle, PG in liver is a degradable source of glucose and readily depleted by fasting, emphasizing that there are structural and regulatory differences in glycogen metabolism among tissues. Both mouse models recapitulate typical histological and physiological features of two human variants of branching enzyme deficiency.