Null mutations and lethal congenital form of glycogen storage disease type IV.
ABSTRACT 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.
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ABSTRACT: Hypomyelination and congenital cataract (HCC, OMIM #610532) is a rare autosomal recessive disorder due to FAM126A mutations characterized by congenital cataract, progressive neurologic impairment, and myelin deficiency in the central and peripheral nervous system. We have identified two novel mutations in three affected members of two unrelated families. Two sibs harbouring a microdeletion causing a premature stop in the protein showed the classical clinical and neuroradiologic HCC picture. The third patient carrying a missense mutation showed a relatively mild clinical picture without peripheral neuropathy. A residual amount of hyccin protein in primary fibroblasts was demonstrated by functional studies indicating that missense mutations are likely to have less detrimental effects if compared with splice-site mutations or deletions that cause the full-blown HCC phenotype, including peripheral nervous system involvement.Biochemical and Biophysical Research Communications 08/2013; · 2.28 Impact Factor
Chapter: Glycogen Storage Disease Type IV[Show abstract] [Hide abstract]
ABSTRACT: 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 diagnosis is suspected based on the clinical presentation and the finding of abnormally branched glycogen accumulation in muscle or liver tissue. The diagnosis is confirmed by the demonstration of glycogen branching enzyme (GBE) deficiency in liver, muscle, or skin fibroblasts, and/or the identification of biallelic mutations in GBE1, the only gene in which mutations are known to cause GSD IV. 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 patients 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 disease-causing mutations have been identified in an affected family member, test at-risk relatives to allow early diagnosis and management of disease manifestations. 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 and prenatal diagnosis for pregnancies at increased risk are possible based on molecular testing if the disease-causing mutations in the family have been identified. If the disease-causing mutations have not been identified, glycogen branching enzyme (GBE) testing on cultured amniocytes can be performed for prenatal diagnosis.GeneReviews™, Edited by Roberta A Pagon, Thomas D Bird, Cynthia R Dolan, Karen Stephens, Margaret P Adam; University of Washington, Seattle.
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ABSTRACT: 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 18.104.22.168) 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 22.214.171.124), 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 GBE repression in glycogenoses can cause pathogenic polyglucosan buildup, which might be corrected by GS inhibition. This article is protected by copyright. All rights reserved.Journal of Neurochemistry 04/2013; · 4.24 Impact Factor