Glycogen storage disease type III: a mixed-methods study to assess the burden of disease

Background

Glycogen storage disease type III (GSD III) is a rare inherited disorder that results from a glycogen debranching enzyme deficiency.

Objectives

The purpose of this research was to collect data on the signs, symptoms, and impacts of GSD III from the perspective of adult patients and caregivers of individuals with GSD III.

Design

Online survey and qualitative interviews.

Methods

Following institutional review board approval, adult patients and caregivers of children with GSD III were recruited through advocacy networks and clinical sites. If eligible, participants were consented, screened, and sent a survey and/or participated in a 60-min interview. The survey and interview included questions about family history, diagnosis, signs and symptoms, impacts, and management of GSD III. Conceptual models were developed following the analysis of results.

Results

In all, 29 adults and 46 caregivers completed the online survey and/or the interviews with 73 survey and 19 interview respondents. Adults and caregivers reported digestive, musculoskeletal, growth and physical appearance, and cardiac signs and symptoms. Liver conditions were reported by most respondents (83%). Adults and caregivers frequently reported impacts such as difficulty keeping up with peers (77%) and difficulty exercising/difficulty with physical activity (53%). Hypoglycemia was frequently reported in both adults and children, with more than half reporting hospitalizations due to hypoglycemia. Caregivers focused on hypoglycemia when reporting signs/symptoms that most interfere with their child's life and prevention of hypoglycemia as a desired outcome for an effective therapy. Adults most often reported muscle weakness as a top interfering symptom and the most important goal of a potential therapy. Impacts were also reported in activities of daily living, cognitive, emotional, work/school, and sleep domains.

Conclusion

Individuals with GSD III experience a broad spectrum of symptoms and disease impacts. There is an unmet need for therapies that improve metabolic control, reduce the burden of dietary management, reduce fatigue and liver problems, and improve muscle strength and function.

French recommendations for the management of glycogen storage disease type III

The aim of the Protocole National De Diagnostic et de Soins/French National Protocol for Diagnosis and Healthcare (PNDS) is to provide advice for health professionals on the optimum care provision and pathway for patients with glycogen storage disease type III (GSD III).The protocol aims at providing tools that make the diagnosis, defining the severity and different damages of the disease by detailing tests and explorations required for monitoring and diagnosis, better understanding the different aspects of the treatment, defining the modalities and organisation of the monitoring. This is a practical tool, to which health care professionals can refer. PNDS cannot, however, predict all specific cases, comorbidities, therapeutic particularities or hospital care protocols, and does not seek to serve as a substitute for the individual responsibility of the physician in front of his/her patient.

Evaluation of Glycogen Storage Patients: Report of Twelve Novel Variants and New Clinical Findings in a Turkish Population

Glycogen storage diseases (GSDs) are clinically and genetically heterogeneous disorders that disturb glycogen synthesis or utilization. Although it is one of the oldest inherited metabolic disorders, new genetic methods and long-time patient follow-ups provide us with unique insight into the genotype-phenotype correlations. The aim of this study was to share the phenotypic features and molecular diagnostic results that include new pathogenic variants in our GSD cases. Twenty-six GSD patients were evaluated retrospectively. Demographic data, initial laboratory and imaging features, and current findings of the patients were recorded. Molecular analysis results were classified as novel or previously defined variants. Novel variants were analyzed with pathogenicity prediction tools according to American College of Medical Genetics and Genomics (ACGM) criteria. Twelve novel and rare variants in six different genes were associated with the disease. Hearing impairment in two patients with GSD I, early peripheral neuropathy after liver transplantation in one patient with GSD IV, epilepsy and neuromotor retardation in three patients with GSD IXA were determined. We characterized a heterogeneous group of all diagnosed GSDs over a 5-year period in our institution, and identified novel variants and new clinical findings. It is still difficult to establish a genotype-phenotype correlation in GSDs.

Narrative review of glycogen storage disorder type III with a focus on neuromuscular, cardiac and therapeutic aspects

Glycogen storage disorder type III (GSDIII) is a rare inborn error of metabolism due to loss of glycogen debranching enzyme activity, causing inability to fully mobilize glycogen stores and its consequent accumulation in various tissues, notably liver, cardiac and skeletal muscle. In the pediatric population, it classically presents as hepatomegaly with or without ketotic hypoglycemia and failure to thrive. In the adult population, it should also be considered in the differential diagnosis of left ventricular hypertrophy or hypertrophic cardiomyopathy, myopathy, exercise intolerance, as well as liver cirrhosis or fibrosis with subsequent liver failure. In this review article, we first present an overview of the biochemical and clinical aspects of GSDIII. We then focus on the recent findings regarding cardiac and neuromuscular impairment associated with the disease. We review new insights into the pathophysiology and clinical picture of this disorder, including symptomatology, imaging and electrophysiology. Finally, we discuss current and upcoming treatment strategies such as gene therapy aimed at the replacement of the malfunctioning enzyme to provide a stable and long-term therapeutic option for this debilitating disease.

The Novel Compound Heterozygous Mutations in the AGL Gene in a Chinese Family With Adult Late-Onset Glycogen Storage Disease Type IIIa

Objective: To investigate the clinical features, skeletal muscle imaging, and muscle pathological characteristics of late-onset GSD IIIa caused by mutation of the AGL gene in adults.

Methods: The clinical data, skeletal muscle imaging, pathological data, and gene test results of a family with late-onset GSD IIIa in adulthood were collected in detail in November 2019.

Results: The proband is a 40-years-old male, who was admitted into our hospital due to a 2-years history of limb weakness. The proband was diagnosed with the following syndrome: he had a 15-years history of elevated muscle enzymes; the cranial nerve examinations showed no abnormal findings; the muscle tension in both upper and lower limbs was low, and tendon reflexes were absent; the proband's muscle strength was 5 in the proximal muscles and 4 in the distal muscles of the upper limbs, with 3 in the proximal muscles and 4 in the distal muscles of the lower limbs; Magnetic Resonance Imaging (MRI) revealed abnormally high signal intensity changes in the posterior thigh muscle group, and the posterior-medial calf muscle group; and vacuoles were evident in some muscle fibers biopsied from the gastrocnemius muscle. Periodic acid-Schiff staining stained the cytoplasm of muscle fibers a dark red color. The proband's older brother exhibited the same clinical features. DNA analysis identified mutations in the AGL gene in the proband, his older brother, and parents. The proband and his older brother both carried two compound heterozygous mutations, c.866G>A and c.2855_2856insT. Pedigree analysis demonstrated that c.866G>A and c.2855_2856insT mutations had been inherited from the mother and father, respectively.

Conclusion: Late-onset GSD IIIa in adults is clinically characterized by muscle weakness, muscle atrophy, and mainly occurred in the posterior thigh muscle group. We also identified two novel compound heterozygous mutations (c.866G> A and c.2855_2856insT) in the AGL gene.

Incidence of inherited metabolic disorders in southern Israel: a comparison between consanguinity and non-consanguinity communities

Background

Inherited metabolic disorders (IMDs) are group of rare monogenic diseases, usually derived from reduced or absent activity in a single metabolic pathway. Most of the IMDs are inherited in an autosomal recessive manner. The incidence of IMDs varies from country to country and within different ethnic groups, but data is still scarce. Consanguinity rate among populations is highly contributor factor for IMDs incidence. There are no reports comparing the incidence of IMD in consanguineous and non-consanguineous populations from the same geographic region with the same diagnostic capabilities. Our study objective is to compare the incidence of IMDs between between the relatively low consanguineous Jewish population and the consanguineous Bedouin population, both living in the southern of Israel.

Results

During 1990–2017 there were 393,772 live births in the Negev district, of Southern of Israel. Among them 187,049 were of Jewish origin while 206,723 were of Bedouin-Muslim origin. A total of 223 children were diagnosed in this study period with IMDs. Among those 223 children with IMD, 33 were of Jewish origin while the other 190 children were of Bedouin-Muslim origin. The overall incidence for IMDs of the overall Negev population was 56.6/100,000 live birth. The incidence for IMD's among the Bedouin population was significantly higher than among Jewish population.

Conclusions

IMDs are extremely more common in the consanguineous Bedouin compared with the relatively non-consanguineous Jewish population of Southern Israel. Health policy makers should consider these data and prepare educational and genetic counselling problems accordingly.

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.

[Molecular and clinical characterization of Colombian patients suffering from type III glycogen storage disease]

INTRODUCTION

Type III glycogen storage disease (GSD III) is an autosomal recessive disorder in which a mutation in the AGL gene causes deficiency of the glycogen debranching enzyme. The disease is characterized by fasting hypoglycemia, hepatomegaly and progressive myopathy. Molecular analyses of AGL have indicated heterogeneity depending on ethnic groups. The full spectrum of AGL mutations in Colombia remains unclear.

OBJECTIVE

To describe the clinical and molecular characteristics of ten Colombian patients diagnosed with GSD III.

MATERIALS AND METHODS

We recruited ten Colombian children with a clinical and biochemical diagnosis of GSD III to undergo genetic testing. The full coding exons and the relevant exon-intron boundaries of the AGL underwent Sanger sequencing to identify mutation.

RESULTS

All patients had the classic phenotype of the GSD III. Genetic analysis revealed a mutation p.Arg910X in two patients. One patient had the mutation p.Glu1072AspfsX36, and one case showed a compound heterozygosity with p.Arg910X and p.Glu1072AspfsX36 mutations. We also detected the deletion of AGL gene 3, 4, 5, and 6 exons in three patients. The in silico studies predicted that these defects are pathogenic. No mutations were detected in the amplified regions in three patients.

CONCLUSION

We found mutations and deletions that explain the clinical phenotype of GSD III patients. This is the first report with a description of the clinical phenotype and the spectrum of AGL mutations in Colombian patients. This is important to provide appropriate prognosis and genetic counseling to the patient and their relatives.

Long term longitudinal study of muscle function in patients with glycogen storage disease type IIIa

Glycogen storage disease type III (GSDIII) is an autosomal recessive disorder caused by mutations in the AGL gene coding for the glycogen debranching enzyme. Current therapy is based on dietary adaptations but new preclinical therapies are emerging. The identification of outcome measures which are sensitive to disease progression becomes critical to assess the efficacy of new treatments in upcoming clinical trials. In order to prepare future longitudinal studies or therapeutic trials with large cohorts, information about disease progression is required. In this study we present preliminary longitudinal data of Motor Function Measure (MFM), timed tests, Purdue pegboard test, and handgrip strength collected over 5 to 9years of follow-up in 13 patients with GSDIII aged between 13 and 56years old. Follow-up for nine of the 13 patients was up to 9years. Similarly to our previous cross-sectional retrospective study, handgrip strength significantly decreased with age in patients older than 37years. MFM scores started to decline after the age of 35. The Purdue pegboard score also significantly reduced with increasing age (from 13years of age) but with large inter-visit variations. The time to stand up from a chair or to climb 4 stairs increased dramatically in some but not all patients older than 30years old. In conclusion, this preliminary longitudinal study suggests that MFM and handgrip strength are the most sensitive muscle function outcome measures in GSDIII patients from the end of their third decade. Sensitive muscle outcome measures remain to be identified in younger GSDIII patients but is challenging as muscle symptoms remain discrete and often present as accumulated fatigue.

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.

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.

Molecular and biochemical characterization of a novel intronic single point mutation in a Tunisian family with glycogen storage disease type III

Genetic deficiency of the glycogen debranching enzyme causes glycogen storage disease type III, an autosomal recessive inherited disorder. The gene encoding this enzyme is designated as AGL gene. The disease is characterized by fasting hypoglycemia, hepatomegaly, growth retardation, progressive myopathy and cardiomyopathy. In the present study, we present clinical features and molecular characterization of two consanguineous Tunisian siblings suffering from Glycogen storage disease type III. The full coding exons of the AGL gene and their corresponding exon-intron boundaries were amplified for the patients and their parents. Gene sequencing identified a novel single point mutation at the conserved polypyrimidine tract of intron 21 in a homozygous state (IVS21-8A>G). This variant cosegregated with the disease and was absent in 102 control chromosomes. In silico analysis using online resources showed a decreased score of the acceptor splice site of intron 21. RT-PCR analysis of the AGL splicing pattern revealed a 7 bp sequence insertion between exon 21 and exon 22 due to the creation of a new 3' splice site. The predicted mutant enzyme was truncated by the loss of 637 carboxyl-terminal amino acids as a result of premature termination. This novel mutation is the first mutation identified in the region of Bizerte and the tenth AGL mutation identified in Tunisia. Screening for this mutation can improve the genetic counseling and prenatal diagnosis of GSD III.

A c.3216_3217delGA mutation in AGL gene in Tunisian patients with a glycogen storage disease type III: evidence of a founder effect

Glycogen storage disease type III (GSD III) is an autosomal recessive disorder characterized by excessive accumulation of abnormal glycogen in the liver and muscles and caused by deficiency in the glycogen debranching enzyme, the amylo-1,6-glucosidase (AGL). In this study, we report the clinical, biochemical and genotyping features of five unrelated GSD III patients coming from the same region in Tunisia. The concentration of erythrocyte glycogen and AGL activity were measured by colorimetric and fluorimetric methods, respectively. Four CA/TG microsatellite markers flanking the AGL gene in chromosome 1 were amplified with fluoresceinated primers. The full coding exons and their relevant exon-intron boundaries of the AGL gene were directly sequenced for the patients and their parents. All patients showed a striking increase of erythrocytes glycogen content. No AGL activity was detected in peripheral leukocytes. Sequencing of the AGL gene identified a c.3216_3217delGA (p.Glu1072AspfsX36) mutation in the five patients which leads to a premature termination, abolishing the AGL activity. Haplotype analysis showed that the mutation was associated with a common homozygote haplotype. Our results suggested the existence of a founder effect responsible for GSD III in this region of Tunisia.

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.

Egyptian glycogen storage disease type III - identification of six novel AGL mutations, including a large 1.5 kb deletion and a missense mutation p.L620P with subtype IIId

BACKGROUND

Glycogen storage disease type III (GSD III) is caused by mutations in AGL which encodes for a single protein with two enzyme activities: oligo-1, 4-1, 4-glucantransferase (transferase) and amylo-1, 6-glucosidase. Activity of both enzymes is lost in most patients with GSD III, but in the very rare subtype IIId, transferase activity is deficient. Since the spectrum of AGL mutations is dependent on the ethnic group, we investigated the clinical and molecular characteristics in Egyptian patients with GSD III.

METHODS

Clinical features were examined in five Egyptian patients. AGL was sequenced and AGL haplotypes were determined.

RESULTS

Six novel AGL mutations were identified: a large deletion (c.3481-3588+1417del1525 bp), two insertions (c.1389insG and c.2368insA), two small deletions (c.2223-2224delGT and c.4041delT), and a missense mutation (p.L620P). p.L620P was found in a patient with IIId. Each mutation was located on a different AGL haplotype.

CONCLUSIONS

Our results suggest that there is allelic and phenotypic heterogeneity of GSD III in Egypt. This is the second description of a large deletion in AGL. p.L620P is the second mutation found in GSD IIId.

Biochemical and molecular investigation of two Korean patients with glycogen storage disease type III

BACKGROUND

Glycogen storage disease type III (GSD-III) is an inborn error of glycogen metabolism caused by a deficiency of the glycogen debranching enzyme, amylo-1,6-glucosidase,4-alpha-glucanotransferase (AGL). Here, we describe two unrelated Korean patients with GSD-III and review their clinical and laboratory findings.

METHODS

The patients were 18- and 11-month-old girls. They presented with hepatosplenomegaly, developmental delay and hypotonia. The routine laboratory findings showed an elevated serum aspartate aminotransferase, alanine aminotransferase, creatine kinase and triglyceride levels. The blood lactate and uric acid levels were within normal limits. PCR and direct sequencing were performed to determine genetic findings.

RESULTS

Glycogen quantitation was markedly increased and AGL activity was undetectable in both patients. Sequence analysis of the AGL gene showed that both patients were compound heterozygotes for c.853C>T (p.R285X) and c.1735+1G>T in one patient, and c.2894_2896delGGAinsTG and c.4090G>C (p.D1364H) in the other patient. The c.2894_2896delGGAinsTG and c.4090G>C (p.D1364H) mutation was a novel finding.

CONCLUSIONS

GSD-III should be ruled out when a patient presents with hepatic abnormalities, hypoglycemia, myopathy and hyperlipidemia. This is the first report of confirmation of GSD-III in Korean patients by biochemical and genetic findings.

Comprehensive arrayed primer extension array for the detection of 59 sequence variants in 15 conditions prevalent among the (Ashkenazi) Jewish population

In the Ashkenazi Jewish population, serious and lethal genetic conditions occur with relatively high frequency. A single test that encompasses the majority of population-specific mutations is not currently available. For comprehensive carrier screening and molecular diagnostic purposes, we developed a population-specific and inclusive microarray. The arrayed primer extension genotyping microarray carries 59 sequence variant detection sites, of which 53 are detectable bi-directionally. These sites represent the most common variants in Tay-Sachs disease, Bloom syndrome, Canavan disease, Niemann-Pick A, familial dysautonomia, torsion dystonia, mucolipidosis type IV, Fanconi anemia, Gaucher disease, factor XI deficiency, glycogen storage disease type 1a, maple syrup urine disease, nonsyndromic sensorineural hearing loss, familial Mediterranean fever, and glycogen storage disease type III. Several mutations in the selected disorders that are not prevalent per se in the Ashkenazi Jewish populations, as well pseudodeficiency alleles, are also included in the array. The initial technical evaluation of this microarray demonstrates that it is comprehensive, robust, sensitive, specific, and easily modifiable. This cost-effective array is based on a diversely applied platform technology and is suitable for both carrier screening and disease detection in Ashkenazi and Sephardic Jewish populations.

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.

Molecular characterization of Egyptian patients with glycogen storage disease type IIIa

Glycogen storage disease type IIIa (GSD IIIa) is an autosomal recessive disorder characterized by excessive accumulation of abnormal glycogen in the liver and muscles and caused by a deficiency in the glycogen debranching enzyme. The spectrum of AGL mutations in GSD IIIa patients depends on ethnic group-prevalent mutations have been reported in the North African Jewish population and in an isolate such as the Faroe islands, because of the founder effect, whereas heterogeneous mutations are responsible for the pathogenesis in Japanese patients. To shed light on molecular characteristics in Egypt, where high rate of consanguinity and large family size increase the frequency of recessive genetic diseases, we have examined three unrelated patients from the same area in Egypt. We identified three different individual AGL mutations; of these, two are novel deletions [4-bp deletion (750-753delAGAC) and 1-bp deletion (2673delT)] and one the nonsense mutation (W1327X) previously reported. All are predicted to lead to premature termination, which completely abolishes enzyme activity. Three consanguineous patients are homozygotes for their individual mutations. Haplotype analysis of mutant AGL alleles showed that each mutation was located on a different haplotype. Our results indicate the allelic heterogeneity of the AGL mutation in Egypt. This is the first report of AGL mutations in the Egyptian population.

DNA-based subtyping of glycogen storage disease type III: mutation and haplotype analysis of the AGL gene in Chinese

Glycogen storage disease type III (GSD III) is an inborn error of glycogen metabolism caused by a deficiency of glycogen debranching enzyme (AGL). Here, we investigate two unrelated Hong Kong Chinese GSD III patients and identify a novel 5-base pair deletional mutation, 2715_2719delTCAGAin exon 22, in one patient and a nonsense mutation, 1222C>T (R408X) in exon 11, in another patient. Since GSD IIIb is only caused by mutation in exon 3 of the AGL gene, we diagnose our patients to have GSD IIIa, which is consistent with the clinical diagnosis. Until now, R408X has only been reported in Faroe Islands GSDIII patients and was thought to demonstrate a founder effect. In this study, haplotyping of the disease-bearing chromosomes in the AGL locus by 19 intragenic single nucleotide polymorphisms shows that R408X is linked with IVS16+8T and IVS23-21T in our patient while R408X is linked with IVS16+8C and IVS23-21A in the Faroe Islands. The different haplotypes of R408X in Chinese and Faroese indicated that R408X is a recurrent mutation.

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.

A genetic profile of contemporary Jewish populations

The Jews are an ancient people with a history spanning several millennia. Genetic studies over the past 50 years have shed light on Jewish origins, the relatedness of Jewish communities and the genetic basis of Mendelian disorders among Jewish peoples. In turn, these observations have been used to develop genetic testing programmes and, more recently, to attempt to discover new genes for susceptibility to common diseases.

Compound heterozygous patient with glycogen storage disease type III: identification of two novel AGL mutations, a donor splice site mutation of Chinese origin and a 1-bp deletion of Japanese origin

Glycogen storage disease type III (GSD III) is an autosomal recessive disorder caused by deficiency of glycogen-debranching enzyme (AGL). We studied a 2-year-old GSD III patient whose parents were from different ethnic groups. Nucleotide sequence analysis of the patient showed two novel mutations: a single cytosine deletion at nucleotide 2399 (2399delC) in exon 16, and a G-to-A transition at the +5 position at the donor splice site of intron 33 (IVS33+5G>A). Analysis of the mRNA produced by IVS33+5G>A showed aberrant splicing: skipping of exon 33 and activation of a cryptic splice site in exon 34. Mutational analysis of the family revealed that the 2399delC was inherited from her father, who is of Japanese origin, and the IVS33+5G>A from her mother, who is of Chinese descent, establishing that the patient was a compound heterozygote. To our knowledge, this is the first report of a mutation identified in a GSD III patient from the Chinese population.

Congenital insensitivity to pain with anhidrosis (CIPA) in Israeli-Bedouins: genetic heterogeneity, novel mutations in the TRKA/NGF receptor gene, clinical findings, and results of nerve conduction studies

Congenital insensitivity to pain with anhidrosis (CIPA), a rare and severe disorder, comprises absence of sensation to noxious stimuli, inability to sweat, and recurrent episodes of hyperthermia. It has a relatively high prevalence in the consanguineous Israeli-Bedouins. Clinical studies of 28 patients are reported here. Using the linkage analysis approach, we linked the disease in 9 of 10 unrelated Israeli-Bedouin families with CIPA to the TrkA gene, which encodes the receptor for nerve growth factor. In one family, linkage was excluded, implying that another gene, yet unidentified, is involved. Two new mutations in the tyrosine kinase domain of the TrkA gene were identified in our CIPA patients: a 1926-ins-T in most of the southern Israeli-Negev CIPA patients, and a Pro- 689-Leu mutation in a different isolate of Bedouins in northern Israel. Eight prenatal diagnoses were made in the southern Israeli-Negev Bedouins, two by linkage analysis and six by checking directly for the 1926-ins-T mutation. Three polymorphisms in the TrkA protein kinase encoding domain were also observed.

Novel mutations in two Japanese cases of glycogen storage disease type IIIa and a review of the literature of the molecular basis of glycogen storage disease type III

We report two novel mutations in two Japanese patients with glycogen storage disease type IIIa (GSD IIIa). In addition, we review the literature on mutations in GSD III to understand better the molecular basis of GSD III. In our first case, the homozygous A-to-C mutation at the acceptor site of intron 5 (IVS5-2A > C) was identified. This leads to the skipping of exon 6 and the predicted mutant protein was found to be 68 amino acids shorter than normal. This is the first report of skipping exon 6, which encodes one of the putative active sites, resulting in a profoundly deleterious effect on debrancher activity. In our second case, the homozygous deletion of an A at position 4234 (4234delA) was identified; this induces a frameshift resulting in the appearance of a stop codon at amino acid position 1276 (1276X). In patients with GSD IIIa, several mutations of the debrancher gene located in the C-terminal region containing putative glycogen binding domains have been identified as well as 4234delA in our second case. On the other hand, specific localization of the mutations within exon 3 was proposed in patients with GSD IIIb.

Glycogen storage myopathies

The glycogen storage myopathies are caused by enzyme defects in the glycogenolytic or in the glycolytic pathway affecting skeletal muscle alone or in conjunction with other tissues. The authors review recent findings in this area, including a new entity, aldolase deficiency, and the wealth of molecular genetic data that are rapidly accumulating. Despite this progress, genotype-phenotyp3 correlations are still murky in most glycogen storage myopathies.

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

Deficiency of glycogen debranching enzyme (AGL) activity causes glycogen storage disease type III (GSD-III). Generalized loss of AGL activity results in GSD-IIIa, and muscle-specific retention of AGL activity results in GSD-IIIb. To date, no common mutation has been described among GSD-III patients, except for three alleles; two linked specifically with GSD-IIIb, and the third found only in North African Jews with GSD-IIIa. Here we report two frequent mutations, each of which was found in the homozygous state in multiple patients, and each of which was associated with a subset of clinical phenotype in those patients with that mutation. A novel point mutation of a single T deletion at cDNA position 3964 (3964delT) was first detected in an African American patient, who has a severe phenotype and early onset of clinical symptoms. The second mutation was an A to G transition at position -12 upstream of the 3' splice site of intron 32 (IVS32-12A > G). This lesion, previously implicated as a IIIb mutation in a Japanese patient, was identified in a confirmed GSD-IIIa Caucasian patient presenting with mild clinical symptoms. These two mutations together account for more than 12% of the molecular defects in the GSD-III patients tested. Our molecular and clinical data suggest a genotype-phenotype correlation for each of these mutations. Furthermore, this current study, coupled with our previous reports, describes the molecular tools necessary for the development of a DNA-based diagnostic test for GSD-III.

The molecular background of glycogen metabolism disorders

The molecular pathology of classical glycogen storage disorders, glycogen synthase deficiency and Fanconi-Bickel syndrome is reviewed. The isolation of the respective cDNAs, the chromosomal localization of the genes and the elucidation of the genomic organization enabled mutation analysis in most disorders. The findings have shed light on the multi-protein structure of the glucose-6-phosphatase system, the phosphorylase kinase enzymatic complex and the molecular background of the differential tissue expression in debranching enzyme deficiency. The immediate practical benefit of these studies is our extending ability to predict the outcome of clinical variants and to offer genetic counseling to most families. The elucidation of the tertiary structure of these proteins and their structure-function relationship poses major challenges for the future.