Genotype-phenotype correlation in two frequent mutations and mutation update in type III glycogen storage disease

A functional mini-GDE transgene corrects impairment in models of glycogen storage disease type III

Glycogen storage disease type III (GSDIII) is a rare inborn error of metabolism affecting liver, skeletal muscle, and heart due to mutations of the AGL gene encoding for the glycogen debranching enzyme (GDE). No curative treatment exists for GSDIII. The 4.6 kb GDE cDNA represents the major technical challenge toward the development of a single recombinant adeno-associated virus-derived (rAAV-derived) vector gene therapy strategy. Using information on GDE structure and molecular modeling, we generated multiple truncated GDEs. Among them, an N-terminal-truncated mutant, ΔNter2-GDE, had a similar efficacy in vivo compared with the full-size enzyme. A rAAV vector expressing ΔNter2-GDE allowed significant glycogen reduction in heart and muscle of Agl-/- mice 3 months after i.v. injection, as well as normalization of histology features and restoration of muscle strength. Similarly, glycogen accumulation and histological features were corrected in a recently generated Agl-/- rat model. Finally, transduction with rAAV vectors encoding ΔNter2-GDE corrected glycogen accumulation in an in vitro human skeletal muscle cellular model of GSDIII. In conclusion, our results demonstrated the ability of a single rAAV vector expressing a functional mini-GDE transgene to correct the muscle and heart phenotype in multiple models of GSDIII, supporting its clinical translation to patients with GSDIII.

Spectrum of amyloglucosidase mutations in Asian Indian patients with Glycogen storage disease type III

Glycogen storage disease type III (GSD III) is a rare autosomal recessive inborn error of glycogen degradation pathway due to deficiency or reduced activity of glycogen debranching enzyme (GDE) that results in accumulation of abnormal glycogen in the liver, muscle, and heart. The cardinal hallmarks are hepatomegaly, fasting hypoglycemia, seizures, growth retardation, progressive skeletal myopathy, and cardiomyopathy in few. To date, 258 mutations in amyloglucosidase (AGL) gene have been identified worldwide. However, the mutation spectrum in the Asian Indian region is yet to be well characterized. We investigated 24 patients of Asian origin from 21 unrelated families with a provisional diagnosis of GSD III based on clinical and biochemical criteria. Molecular diagnosis was assessed by bidirectional sequencing and the impact of novel missense variants on the tertiary (three-dimensional) structure of GDE was evaluated by molecular modeling approach. Eighteen different pathogenic variants were identified, out of which 78% were novel. Novel variants included five nonsense, three small duplications and two small deletions, a splice site variant, and three missense variants. Variations in Exons 4, 14, 19, 24, 27, and 33 accounted for 61% of the total pathogenic variants identified and Allele p.Gly798Alafs*3 showed a high allele frequency of 11%. Molecular modeling study of novel pathogenic missense variants indicated the probable underlying molecular mechanism of adverse impact of variations on the structure and catalytic function of human GDE. Our study is the first large study on GSD III from the Asian subcontinent, which further expands the mutation spectrum of AGL.

Intron retention is among six unreported AGL mutations identified in Malaysian GSD III patients

BACKGROUND

Glycogen storage disease type III is an autosomal recessive disorder that is caused by deficiencies of the glycogen debranching enzyme. Mutations within the AGL gene have been found to be heterogeneous, with some common mutations being reported in certain populations. The mutation spectrum of AGL gene in the multi-ethnic Malaysian population is still unknown.

OBJECTIVE

The present study seeks to determine the mutation spectrum of the AGL gene in Malaysian population.

METHODS

A total of eleven patients (eight Malay, two Chinese and one Bajau) were investigated. Genomic DNA was extracted and subsequently the AGL gene was amplified using specific primers and sequenced. Mutations found were screened in 150 healthy control samples either by restriction enzyme digestion assay or TaqMan^® SNP Genotyping assay.

RESULTS

We identified six unreported mutations (c.1423+1G>T, c.2914_2915delAA, c.3814_3815delAG, c.4333T>G, c.4490G>A, c.4531_4534delTGTC) along with three previously reported mutations (c.99C>T, c.1783C>T, c.2681+1G>A). One of the six unreported mutation causes abnormal splicing and results in retention of intron 12 of the mature transcript, while another is a termination read-through. One of the reported mutation c.2681+1G>A was recurrently found in the Malay patients (n = 7 alleles; 31.8%).

CONCLUSION

The mutation spectrum of the AGL gene in Malaysian patients has shown considerable heterogeneity, and all unreported mutations were absent in all 150 healthy control samples tested.

A Novel Nonsense Mutation of the AGL Gene in a Romanian Patient with Glycogen Storage Disease Type IIIa

Background. Glycogen storage disease type III (GSDIII) is a rare metabolic disorder with autosomal recessive inheritance, caused by deficiency of the glycogen debranching enzyme. There is a high phenotypic variability due to different mutations in the AGL gene. Methods and Results. We describe a 2.3-year-old boy from a nonconsanguineous Romanian family, who presented with severe hepatomegaly with fibrosis, mild muscle weakness, cardiomyopathy, ketotic fasting hypoglycemia, increased transaminases, creatine phosphokinase, and combined hyperlipoproteinemia. GSD type IIIa was suspected. Accordingly, genomic DNA of the index patient was analyzed by next generation sequencing of the AGL gene. For confirmation of the two mutations found, genetic analysis of the parents and grandparents was also performed. The patient was compound heterozygous for the novel mutation c.3235C>T, p.Gln1079(⁎) (exon 24) and the known mutation c.1589C>G, p.Ser530(⁎) (exon 12). c.3235 >T, p.Gln1079(⁎) was inherited from the father, who inherited it from his mother. c.1589C>G, p.Ser530(⁎) was inherited from the mother, who inherited it from her father. Conclusion. We report the first genetically confirmed case of a Romanian patient with GSDIIIa. We detected a compound heterozygous genotype with a novel mutation, in the context of a severe hepatopathy and an early onset of cardiomyopathy.

Capture-based high-coverage NGS: a powerful tool to uncover a wide spectrum of mutation types

PURPOSE

Next-generation sequencing (NGS) has been widely applied to clinical diagnosis. Target-gene capture followed by deep sequencing provides unbiased enrichment of the target sequences, which not only accurately detects single-nucleotide variations (SNVs) and small insertion/deletions (indels) but also provides the opportunity for the identification of exonic copy-number variants (CNVs) and large genomic rearrangements.

METHOD

Capture NGS has the ability to easily detect SNVs and small indels. However, genomic changes involving exonic deletions/duplications and chromosomal rearrangements require more careful analysis of captured NGS data. Misaligned raw sequence reads may be more than just bad data. Some mutations that are difficult to detect are filtered by the preset analytical parameters. "Loose" filtering and alignment conditions were used for thorough analysis of the misaligned NGS reads. Additionally, using an in-house algorithm, NGS coverage depth was thoroughly analyzed to detect CNVs.

RESULTS

Using real examples, this report underscores the importance of the accessibility to raw sequence data and manual review of suspicious sequence regions to avoid false-negative results in the clinical application of NGS. Assessment of the NGS raw data generated by the use of loose filtering parameters identified several sequence aberrations, including large indels and genomic rearrangements. Furthermore, NGS coverage depth analysis identified homozygous and heterozygous deletions involving single or multiple exons.

CONCLUSION

Our results demonstrate the power of deep NGS in the simultaneous detection of point mutations and intragenic exonic deletion in one comprehensive step.Genet Med 18 5, 513-521.

Inherent lipid metabolic dysfunction in glycogen storage disease IIIa

We studied two patients from a nonconsanguineous family with life-long abnormal liver function, hepatomegaly and abnormal fatty acid profiles. Abnormal liver function, hypoglycemia and muscle weakness are observed in various genetic diseases, including medium-chain acyl-CoA dehydrogenase (MCAD) deficiency and glycogen storage diseases. The proband showed increased free fatty acids, mainly C8 and C10, resembling fatty acid oxidation disorder. However, no mutation was found in ACADM and ACADL gene. Sequencing of theamylo-alpha-1, 6-glucosidase, 4-alpha-glucanotransferase (AGL) gene showed that both patients were compound heterozygotes for c.118C > T (p.Gln40X) and c.753_756 del CAGA (p.Asp251Glufsx29), whereas their parents were each heterozygous for one of these mutations. The AGL protein was undetectable in EBV-B cells from the two patients. Transcriptome analysis demonstrated a significant different pattern of gene expression in both of patients’ cells, including genes involving in the PPAR signaling pathway, fatty acid biosynthesis, lipid synthesis and visceral fat deposition and metabolic syndrome. This unique gene expression pattern is probably due to the absence of AGL, which potentially accounts for the observed clinical phenotypes of hyperlipidemia and hepatocyte steatosis in glycogen storage disease type IIIa.

A founder splice site mutation underlies glycogen storage disease type 3 in consanguineous Saudi families

BACKGROUND AND OBJECTIVES

Glycogen storage disease type 3 (GSD III) is an autosomal recessive disorder caused by genetic mutations in the gene AGL. AGL encodes amylo-a-1, 6-glucosidase, 4-a-glucanotransferase, a glycogen debranching enzyme. GSD III is characterized by fasting hypoglycemia, hepatomegaly, growth retardation, progressive myopathy, and cardiomyopathy due to storage of abnormally structured glycogen in both skeletal and cardiac muscles and/or liver. The aim of this study is to detect mutations underlying GSD III in Saudi patients.

DESIGN AND SETTINGS

A cross-sectional clinical genetic study of 5 Saudi consanguineous families examined at the metabolic clinic of the Madinah Maternity and Children Hospital.

PATIENTS AND METHODS

We present a biochemical and molecular analysis of 5 consanguineous Saudi families with GSD III. DNA was isolated from the peripheral blood of 31 individuals, including 12 patients, and the AGL gene was sequenced bidirectionally. DNA sequences were compared with the AGL reference sequence from the ensemble genome browser.

RESULTS

Genotyping and sequence analysis identified a homozygous intronic splice acceptor site mutation (IVS32-12A > G) in 4 families perfectly segregating with the phenotype. Complementary (c)DNA sequence analysis of the AGL gene revealed an 11-bp sequence insertion between exon 32 and exon 33 due to the creation of a new 3' splice site. The predicted mutant enzyme was truncated by 112 carboxyl-terminal amino acids as a result of premature termination.

CONCLUSION

Haplotype analysis revealed that the mutation arises as a result of founder effect, not an independent event. This is the first report of a genetic mutation in the AGL gene from Saudi Arabia. Screening for this mutation can improve genetic counseling and prenatal diagnosis of GSD III in Saudi Arabia.

A mutation analysis of the AGL gene in Korean patients with glycogen storage disease type III

Glycogen storage disease type III (GSD III) is an autosomal recessive disorder that is characterized by the excessive accumulation of abnormal glycogen in the liver and muscles and is caused by a deficiency in glycogen debranching enzyme (amylo-1,6-glucosidase, 4-alpha-glucanotransferase (AGL)) activity. To investigate the molecular characteristics of GSD III patients in Korea, we have sequenced the AGL gene in eight children with GSD III. All patients were compound heterozygotes. We identified 10 different mutations (five novel and five previously reported). The novel mutations include one nonsense (c.1461G>A, p.W487X), three splicing (c.293+4_293+6delAGT in IVS4, c.460+1G>T in IVS5, c.2682-8A>G in IVS21) and one missense mutation (c.2591G>C, p.R864P). Together, p.R285X, c.1735+1G>T and p.L1139P accounted for 56% of all alleles, while the remaining mutations are heterogeneous. These three mutations can be common in Korea, and further larger studies are needed to confirm our findings.

Mutation Analysis in Glycogen Storage Disease Type III Patients in the Netherlands: Novel Genotype-Phenotype Relationships and Five Novel Mutations in the AGL Gene

Glycogen Storage Disease type III (GSD III) is an autosomal recessive disorder in which a mutation in the AGL gene causes deficiency of the glycogen debranching enzyme. In childhood, it is characterized by hepatomegaly, keto-hypoglycemic episodes after short periods of fasting, and hyperlipidemia. In adulthood, myopathy, cardiomyopathy, and liver cirrhosis are the main complications. To determine the genotype of the GSD III patients (n = 14) diagnosed and treated in our center, mutation analysis was performed by either denaturing gradient gel electrophoresis or full gene sequencing. We developed, validated and applied both methods, and in all patients a mutation was identified on both alleles. Five novel pathogenic mutations were identified in seven patients, including four missense mutations (c.643G>A, p.Asp215Asn; c.655A>G, p.Asn219Asp; c.1027C>T, p.Arg343Trp; c.1877A>G, p.His626Arg) and one frameshift mutation (c.3911delA, p.Asn1304fs). The c.643G>A, p.Asp215Asn mutation is related with type IIIa, as this mutation was found homozygously in two type IIIa patients. In addition to five novel mutations, we present new genotype-phenotype relationships for c.2039G>A, p.Trp680X; c.753_756delCAGA, p.Asp251fs; and the intron 32 c.4260-12A>G splice site mutation. The p.Trp680X mutation was found homozygously in four patients, presenting a mild IIIa phenotype with mild skeletal myopathy, elevated CK values, and no cardiomyopathy. The p.Asp251fs mutation was found homozygously in one patient presenting with a severe IIIa phenotype, with skeletal myopathy, and severe symptomatic cardiomyopathy. The c.4260-12A>G mutation was found heterozygously, together with the p.Arg343Trp mutation in a severe IIIb patient who developed liver cirrhosis and hepatocellular carcinoma, necessitating an orthotopic liver transplantation.

Molecular and biochemical characterization of Tunisian patients with glycogen storage disease type III

Glycogen storage disease type III (GSD III) is an autosomal recessive inborn error of metabolism caused by mutations in the glycogen debranching enzyme amylo-1,6-glucosidase gene, which is located on chromosome 1p21.2. GSD III is characterized by the storage of structurally abnormal glycogen, termed limit dextrin, in both skeletal and cardiac muscle and/or liver, with great variability in resultant organ dysfunction. The spectrum of AGL gene mutations in GSD III patients depends on ethnic group. The most prevalent mutations have been reported in the North African Jewish population and in an isolate such as the Faroe Islands. Here, we present the molecular and biochemical analyses of 22 Tunisian GSD III patients. Molecular analysis revealed three novel mutations: nonsense (Tyr1148X) and two deletions (3033_3036del AATT and 3216_3217del GA) and five known mutations: three nonsense (R864X, W1327X and W255X), a missense (R524H) and an acceptor splice-site mutation (IVS32-12A>G). Each mutation is associated to a specific haplotype. This is the first report of screening for mutations of AGL gene in the Tunisian population.

Glycogen storage disease type III in the Irish population

Glycogen storage disease type III (GSD III) results from mutations of the AGL gene encoding the glycogen debrancher enzyme. The disease has clinical and biochemical heterogeneity reflecting the severity of the AGL mutations. We sought to characterise the molecular defects in our cohort of Irish patients with GSD III. Fifteen patients from eight unrelated Irish families were identified: six males and nine females. The age ranged from 2-39 years old, and all presented in the first 3 years of life. Four patients (of three families) had mild disease with hepatomegaly, mild hypoglycaemia and normal creatine kinase (CK) levels. Five families had more severe disease, with liver and skeletal muscle involvement and elevated CK. Eleven different mutations were identified amongst the eight families. Of the 11, six were novel: p.T512fs, p.S736fs, p.A1400fs, p.K1407fs, p.Y519X and p.D627Y. The family homozygous for p.A1400fs had the most severe phenotype (early-onset hypoglycaemia, massive hepatomegaly, myopathy and hypertrophic cardiomyopathy before age 2 years), which was not halted by aggressive carbohydrate and protein supplementation. Conversely, the only missense mutation identified in the cohort, p.D627Y, was associated with a mild phenotype. The phenotypic diversity in our GSD III cohort is mirrored by the allelic heterogeneity. We describe two novel null mutations in exon 32 in two families with severe GSD III resistant to current treatment modalities. Knowledge of the specific mutations segregating in this cohort may allow for the development of new therapeutic interventions.

SINE indel polymorphism of AGL gene and association with growth and carcass traits in Landrace x Jeju Black pig F(2) population

Genetic polymorphisms in the glycogen debrancher enzyme (AGL) gene were assessed with regard to their association with growth and carcass traits in the F(2) population crossbred Landrace and Jeju (Korea) Black pig. Three genotypes representing the insertion and/or deletion (indel) polymorphisms of short interspersed nuclear element were detected at frequencies of 0.278 (L/L), 0.479 (L/S), and 0.243 (S/S), respectively. The AGL S allele-containing pigs evidenced significantly heavier body weights at birth, the 3rd week, 10th week, and 20th week during developmental stages and higher average daily gains during the late period than were noted in the L/L homozygous pigs (P < 0.05), respectively. However, average daily gains during the early period were not significantly associated with genotype distribution (P > 0.05). With regard to the carcass traits, the S allele pigs (S/-) evidenced significantly heavier carcass weights and thicker backfat than was measured in L/L homozygous pigs (P < 0.05). However, body lengths, meat color, and marbling scores were all found not to be statistically significant (P > 0.05). Consequently, the faster growth rate during the late period and backfat deposition rather than intramuscular fat deposition cause differences in pig productivity according to genotypes of the AGL gene. These findings indicate that the AGL genotypes may prove to be useful genetic markers for the improvement of Jeju Black pig-related crossbreeding systems.

Glycogen storage disease type III-hepatocellular carcinoma a long-term complication?

BACKGROUND/AIMS

Glycogen storage disease III (GSD III) is caused by a deficiency of glycogen-debranching enzyme which causes an incomplete glycogenolysis resulting in glycogen accumulation with abnormal structure (short outer chains resembling limit dextrin) in liver and muscle. Hepatic involvement is considered mild, self-limiting and improves with age. With increased survival, a few cases of liver cirrhosis and hepatocellular carcinoma (HCC) have been reported.

METHODS

A systematic review of 45 cases of GSD III at our center (20 months to 67 years of age) was reviewed for HCC, 2 patients were identified. A literature review of HCC in GSD III was performed and findings compared to our patients.

CONCLUSIONS

GSD III patients are at risk for developing HCC. Cirrhosis was present in all cases and appears to be responsible for HCC transformation There are no reliable biomarkers to monitor for HCC in GSD III. Systematic evaluation of liver disease needs be continued in all patients, despite lack of symptoms. Development of guidelines to allow for systematic review and microarray studies are needed to better delineate the etiology of the hepatocellular carcinoma in patients with GSD III.

Molecular analysis of the AGL gene: heterogeneity of mutations in patients with glycogen storage disease type III from Germany, Canada, Afghanistan, Iran, and Turkey

Glycogen storage disease type III (GSD III) is an autosomal recessive disorder characterized by excessive accumulation of abnormal glycogen in the liver and/or muscles and caused by deficiency in the glycogen debranching enzyme (AGL). Previous studies have revealed that the spectrum of AGL mutations in GSD III patients depends on ethnic grouping. We investigated nine GSD III patients from Germany, Canada, Afghanistan, Iran, and Turkey and identified six novel AGL mutations: one nonsense (W255X), three deletions (1019delA, 3202-3203delTA, and 1859-1869del11-bp), and two splicing mutations (IVS7 + 5G > A and IVS21 + 5insA), together with three previously reported ones (R864X, W1327X, and IVS21 + 1G > A). All mutations are predicted to lead to premature termination, which abolishes enzyme activity. Our molecular study on GSD III patients of different ethnic ancestry showed allelic heterogeneity of AGL mutations. This is the first AGL mutation report for German, Canadian, Afghan, Iranian and Turkish populations.

The cellular fate of glucose and its relevance in type 2 diabetes

Type 2 diabetes is a complex disorder with diminished insulin secretion and insulin action contributing to the hyperglycemia and wide range of metabolic defects that underlie the disease. The contribution of glucose metabolic pathways per se in the pathogenesis of the disease remains unclear. The cellular fate of glucose begins with glucose transport and phosphorylation. Subsequent pathways of glucose utilization include aerobic and anaerobic glycolysis, glycogen formation, and conversion to other intermediates in the hexose phosphate or hexosamine biosynthesis pathways. Abnormalities in each pathway may occur in diabetic subjects; however, it is unclear whether perturbations in these may lead to diabetes or are a consequence of the multiple metabolic abnormalities found in the disease. This review is focused on the cellular fate of glucose and relevance to human type 2 diabetes.

A simple, rapid test for the differential diagnosis of glycogen storage disease type 3

BACKGROUND

Type 3 glycogen storage disease is an inborn error of metabolism in young infants that often requires extensive workup. However, this disease manifests with few symptoms other than hepatosplenomegaly. At adolescence, this disease may cause myopathy and cardiomyopathy. Since a significant portion of referrals to pediatrics is for evaluation of a hepatosplenomegaly, the differential diagnosis of this disease assumes importance.

METHODS

The clinical and biochemical findings in 26 patients with the type 3 glycogen storage disease were investigated. Biochemical parameters included ALT, AST, total CK and CK-MB.

RESULTS

Changes in ALT, AST and total CK were observed to varying degrees. However, CK was found to be a diagnostic indicator for type 3 glycogen storage disease and appears to be a pathognomic marker.

CONCLUSIONS

Use of CK may reduce the need for extensive diagnostic profiles and aid in the rapid identification and initiation of management for patients presenting with hepatosplenomegaly.

Clinical and genetic variability of glycogen storage disease type IIIa: seven novel AGL gene mutations in the Mediterranean area

Deficiency of amylo-1,6-glucosidase, 4-alpha-glucanotransferase enzyme (AGL or glycogen debrancher enzyme) is responsible for glycogen storage disease type III, a rare autosomal recessive disorder of glycogen metabolism. The AGL gene is located on chromosome 1p21, and contains 35 exons translated in a monomeric protein product. The disease has recognized clinical and biochemical heterogeneity, reflecting the genotype-phenotype heterogeneity among different subjects. The clinical manifestations of GSD III are represented by hepatomegaly, hypoglycemia, hyperlipidemia, short stature and, in a number of subjects, cardiomyopathy and myopathy. In this article, we discuss the genotypic-phenotypic heterogeneity of GSD III by the molecular characterization of mutations responsible for the disease on a collection of 18 independent alleles from the Mediterranean area. We identified by heteroduplex band shift, DNA direct sequencing, and restriction analysis, seven novel mutations (four nonsense point-mutations: R34X, S530X, R1218X, W1398X; two microinsertions: 1072insT and 4724insAA; and one bp deletion: 676DeltaG), together with two new cases carrying a IVS21 + 1 G --> A splicing site mutation previously described in Italian patients. Altogether, 15 alleles were characterized. The correlation between type of mutation and clinical severity was studied in six patients in whom both mutated alleles were detected. Our data confirm the extreme genetic heterogeneity of this disease, thus precluding a strategy of mutation finding based on screening of recurrent common mutations.