Clinical characteristics The clinical manifestations of glycogen storage disease type IV (GSD IV) discussed in this entry span a continuum of different subtypes with variable ages of onset, severity, and clinical features. Clinical findings vary extensively both within and between families. The fatal perinatal neuromuscular subtype presents in utero with fetal akinesia deformation sequence, including decreased fetal movements, polyhydramnios, and fetal hydrops. Death usually occurs in the neonatal period. The congenital neuromuscular subtype presents in the newborn period with profound hypotonia, respiratory distress, and dilated cardiomyopathy. Death usually occurs in early infancy. Infants with the classic (progressive) hepatic subtype may appear normal at birth, but rapidly develop failure to thrive; hepatomegaly, liver dysfunction, and progressive liver cirrhosis; hypotonia; and cardiomyopathy. Without liver transplantation, death from liver failure usually occurs by age five years. Children with the non-progressive hepatic subtype tend to present with hepatomegaly, liver dysfunction, myopathy, and hypotonia; however, they are likely to survive without progression of the liver disease and may not show cardiac, skeletal muscle, or neurologic involvement. The childhood neuromuscular subtype is rare and the course is variable, ranging from onset in the second decade with a mild disease course to a more severe, progressive course resulting in death in the third decade. Diagnosis/testing The diagnosis is established in a proband by the demonstration of glycogen branching enzyme (GBE) deficiency in liver, muscle, or skin fibroblasts or the identification of biallelic pathogenic variants in GBE1 on molecular genetic testing. Management Treatment of manifestations: Management should involve a multidisciplinary team including specialists in hepatology, neurology, nutrition, medical or biochemical genetics, and child development. Liver transplantation is the only treatment option for individuals with the progressive hepatic subtype of GSD IV who develop liver failure; however, the risk for morbidity and mortality is high, in part because of the extrahepatic manifestations of GSD type IV, especially cardiomyopathy. Children with skeletal myopathy and/or hypotonia warrant developmental evaluation and physical therapy as needed. Those with cardiomyopathy warrant care by a cardiologist. Heart transplant may be an option in individuals with severe cardiac involvement. Prevention of secondary complications: Prevent nutritional deficiencies (e.g., of fat-soluble vitamins) by ensuring adequate dietary intake; prevent perioperative bleeding by assessment of a coagulation profile and use of fresh frozen plasma as needed. Surveillance: No clinical guidelines for surveillance are available. The following evaluations are suggested (with frequency varying according to disease severity): liver function tests including liver transaminases, albumin, and coagulation profile (PT and PTT); abdominal ultrasound examination; echocardiogram; neurologic assessment; nutritional assessment. If cardiomyopathy was not observed on baseline screening echocardiogram at the time of initial diagnosis, repeat echocardiograms every three months during infancy, every six months during early childhood, and annually thereafter. Evaluation of relatives at risk: If the GBE1 pathogenic variants have been identified in an affected family member, test at-risk relatives to allow for early diagnosis and management of disease manifestations. Genetic counseling GSD IV is inherited in an autosomal recessive manner. Each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Although affected sibs are expected to manifest the same subtype of GSD IV, the age of onset and presentation may differ. Carrier testing for at-risk family members and prenatal testing for pregnancies at increased risk are possible based on molecular testing if the pathogenic variants in the family have been identified. If the pathogenic variants have not been identified, GBE testing on cultured amniocytes can be performed for prenatal diagnosis.

Glycogen Storage Disease Type IV

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.

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

Branching enzyme deficiency/glycogenosis storage disease type IV presenting as a severe congenital hypotonia: muscle biopsy and autopsy findings, biochemical and molecular genetic studies.

Uncontrolled elongation of glycogen chains, not adequately balanced by their branching, leads to the formation of an insoluble, presumably neurotoxic, form of glycogen called polyglucosan. To test the suspected pathogenicity of polyglucosans in neurological glycogenoses, we have modeled the typical glycogenosis Adult Polyglucosan Body Disease (APBD) by suppressing glycogen branching enzyme 1 (GBE1, EC 2.4.1.18) expression using lentiviruses harboring short hairpin RNA (shRNA). GBE1 suppression in embryonic cortical neurons led to polyglucosan accumulation and associated apoptosis, which were reversible by rapamycin or starvation treatments. Further analysis revealed that rapamycin and starvation led to phosphorylation and inactivation of glycogen synthase (GS, EC 2.4.1.11), dephosphorylated and activated in the GBE1-suppressed neurons. These protective effects of rapamycin and starvation were reversed by overexpression of phosphorylation site mutant GS only if its glycogen binding site was intact. While rapamycin and starvation induce autophagy, autophagic maturation was not required for their corrective effects, which prevailed even if autophagic flux was inhibited by vinblastine. Furthermore, polyglucosans were not observed in any compartment along the autophagic pathway. Our data suggest that glycogen branching enzyme repression in glycogenoses can cause pathogenic polyglucosan buildup, which might be corrected by GS inhibition.





Knockdown of glycogen branching enzyme in neurons led to accumulation of an insoluble form of glycogen called polyglucosan, to apoptosis and to activation of glycogen synthase. These effects were reversed by glycogen synthase inhibition through starvation and rapamycin treatments, suggesting a potential therapeutic value of glycogen synthase inhibition for treating glycogen storage disorders.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/jnc.12277

Polyglucosan neurotoxicity caused by glycogen branching enzyme deficiency can be reversed by inhibition of glycogen synthase.

Diffuse reticuloendothelial system involvement in type IV glycogen storage disease with a novel GBE1 mutation: a case report and review.

Glycogen storage disease type IV (GSD IV, or Andersen disease) is an autosomal recessive disorder due to the deficiency of 1,4-α-glucan branching enzyme (or glycogen branching enzyme, GBE1), resulting in an accumulation of amylopectin-like polysaccharide in muscle, liver, heart and central and peripheral nervous system. Typically, the presentation is in childhood with liver involvement up to cirrhosis. The neuromuscular form varies in onset (congenital, perinatal, juvenile and adult) and in severity. Congenital cases are rare, and fewer than 20 cases have been described and genetically determined so far. This form is characterized by polyhydramnios, neonatal hypotonia, and neuronal involvement; hepatopathy is uncommon, and the babies usually die between 4 weeks and 4 months of age. We report the case of an infant who presented severe hypotonia, dilatative cardiomyopathy, mild hepatopathy, and brain lateral ventricle haemorrhage, features consistent with the congenital form of GSD IV. He died at one month of life of cardiorespiratory failure. Muscle biopsy and heart and liver autoptic specimens showed many vacuoles filled with PAS-positive diastase-resistant materials. Electron-microscopic analysis showed mainly polyglucosan accumulations in all the tissues examined. Postmortem examination showed the presence of vacuolated neurons containing this abnormal polysaccharide. GBE1 biochemical activity was virtually absent in muscle and fibroblasts, and totally lacking in liver and heart as well as glycogen synthase activity. GBE1 gene sequence analysis revealed a novel homozygous nonsense mutation, p.E152X, in exon 4, correlating with the lack of enzyme activity and with the severe neonatal involvement. Our findings contribute to increasing the spectrum of mutation associated with congenital GSD IV.

Neuropathological study of skeletal muscle, heart, liver, and brain in a neonatal form of glycogen storage disease type IV associated with a new mutation in GBE1 gene.

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Neuropathological study of skeletal muscle, heart, liver, and brain in a neonatal form of glycogen storage disease type IV associated with a new mutation in GBE1 gene.