Glycosylation, hypogammaglobulinemia, and resistance to viral infections

Genetic defects in MOGS, the gene encoding mannosyl-oligosaccharide glucosidase (the first enzyme in the processing pathway of N-linked oligosaccharide), cause the rare congenital disorder of glycosylation type IIb (CDG-IIb), also known as MOGS-CDG. MOGS is expressed in the endoplasmic reticulum and is involved in the trimming of N-glycans. We evaluated two siblings with CDG-IIb who presented with multiple neurologic complications and a paradoxical immunologic phenotype characterized by severe hypogammaglobulinemia but limited clinical evidence of an infectious diathesis. A shortened immunoglobulin half-life was determined to be the mechanism underlying the hypogammaglobulinemia. Impaired viral replication and cellular entry may explain a decreased susceptibility to infections.

Phase I/II trial of adeno-associated virus-mediated alpha-glucosidase gene therapy to the diaphragm for chronic respiratory failure in Pompe disease: initial safety and ventilatory outcomes

Pompe disease is an inherited neuromuscular disease caused by deficiency of lysosomal acid alpha-glucosidase (GAA) leading to glycogen accumulation in muscle and motoneurons. Cardiopulmonary failure in infancy leads to early mortality, and GAA enzyme replacement therapy (ERT) results in improved survival, reduction of cardiac hypertrophy, and developmental gains. However, many children have progressive ventilatory insufficiency and need additional support. Preclinical work shows that gene transfer restores phrenic neural activity and corrects ventilatory deficits. Here we present 180-day safety and ventilatory outcomes for five ventilator-dependent children in a phase I/II clinical trial of AAV-mediated GAA gene therapy (rAAV1-hGAA) following intradiaphragmatic delivery. We assessed whether rAAV1-hGAA results in acceptable safety outcomes and detectable functional changes, using general safety measures, immunological studies, and pulmonary functional testing. All subjects required chronic, full-time mechanical ventilation because of respiratory failure that was unresponsive to both ERT and preoperative muscle-conditioning exercises. After receiving a dose of either 1×10(12) vg (n=3) or 5×10(12) vg (n=2) of rAAV1-hGAA, the subjects' unassisted tidal volume was significantly larger (median [interquartile range] 28.8% increase [15.2-35.2], p<0.05). Further, most patients tolerated appreciably longer periods of unassisted breathing (425% increase [103-851], p=0.08). Gene transfer did not improve maximal inspiratory pressure. Expected levels of circulating antibodies and no T-cell-mediated immune responses to the vector (capsids) were observed. One subject demonstrated a slight increase in anti-GAA antibody that was not considered clinically significant. These results indicate that rAAV1-hGAA was safe and may lead to modest improvements in volitional ventilatory performance measures. Evaluation of the next five patients will determine whether earlier intervention can further enhance the functional benefit.

Crystallization and preliminary X-ray crystallographic analysis of α-glucosidase HaG from Halomonas sp. strain H11

The α-glucosidase HaG from the halophilic bacterium Halomonas sp. strain H11 catalyzes the hydrolysis of the glucosidic linkage at the nonreducing end of α-glucosides, such as maltose and sucrose, to release α-glucose. Based on its amino-acid sequence, this enzyme is classified as a member of glycoside hydrolase family 13. HaG has three unique characteristics: (i) a very narrow substrate specificity, almost exclusively hydrolyzing disaccharides; (ii) activation by monovalent cations, such as K(+), Rb(+), Cs(+) and NH4(+); and (iii) high transfer activity of the glucose moiety to the OH group of low-molecular-weight compounds, including glycerol and 6-gingerol. Crystallographic studies have been performed in order to understand these special features. An expression vector was constructed and recombinant HaG protein was overexpressed, purified and crystallized. A data set to 2.15 Å resolution was collected and processed. The crystal belonged to space group P212121, with unit-cell parameters a = 60.2, b = 119.2, c = 177.2 Å. The structure has been determined by molecular replacement using the isomaltulose synthase PalI as the search model (PDB entry 1m53).

Digestion in adult females of the leaf-footed bug Leptoglossus zonatus (Hemiptera: Coreidae) with emphasis on the glycoside hydrolases α-amylase, α-galactosidase, and α-glucosidase

The leaffooted bug, Leptoglossus zonatus (Hemiptera: Coreidae) is an emerging pest of several crops around the World and up to now very little is known of its digestive system. In this article, glycoside hydrolase (carbohydrase) activities in the adult midgut cells and in the luminal contents of L. zonatus adult females were studied. The results showed the distribution of digestive carbohydrases in adults of this heteropteran species in the different intestinal compartments. Determination of the spatial distribution of α-glucosidase activity in L. zonatus midgut showed only one major molecular form, which was not equally distributed between soluble and membrane-bound isoforms, being more abundant as a membrane-bound enzyme. The majority of digestive carbohydrases were found in the soluble fractions. Activities against starch, maltose and the synthetic substrate NPαGlu were found to show the highest levels of activity, followed by enzymes active against galactosyl oligosaccharides. Based on ion-exchange chromatography elution profiles and banding patterns in mildly denaturing electrophoresis, both midgut α-amylases and α-galactosidases showed at least two isoforms. The data suggested that the majority of carbohydrases involved in initial digestion were present in the midgut lumen, whereas final digestion of starch and of galactosyl oligosaccharides takes place partially within the lumen and partially at the cell surface. The complex of carbohydrases here described was qualitatively appropriate for the digestion of free oligosaccharides and oligomaltodextrins released by α-amylases acting on maize seed starch granules.

Late-onset Pompe disease is prevalent in unclassified limb-girdle muscular dystrophies

OBJECTIVE

Late-onset Pompe disease is a rare, but potentially treatable metabolic myopathy, and therefore should not be overlooked. However, it is not unusual that patients go undiagnosed for many years. We hypothesized that patients with late-onset Pompe disease may have been overlooked in a population of patients with unclassified neuromuscular disease.

METHODS

We used DBS (dried blood spots) to screen for Pompe disease in the two largest neuromuscular clinics and one of the main respiratory centers in Denmark. We selected patients with unclassified LGDM (limb-girdle muscular dystrophy), idiopathic elevation of creatine kinase, unexplained myopathy on muscle biopsy, unexplained restrictive respiratory insufficiency or unspecified myopathy for screening.

RESULTS

177 patients were found eligible for inclusion, and 103 (58.2%) patients accepted screening. Three patients with Pompe disease were identified with DBS, and subsequent genetic testing revealed known pathogenic mutations in the GAA gene. All three patients were found among 38 patients with unclassified LGMD (8%).

CONCLUSION

Our findings indicate that a DBS should be considered early in the diagnostic work-up of patients with an LGMD phenotype, to rule out Pompe disease. Retrospectively, all 3 patients presented with "red flags" more compatible with Pompe disease than LGMD, including; 1) mild non-dystrophic, myopathic features on muscle biopsy, 2) creatine kinase levels below 1000, and 3) disproportionate axial and respiratory muscle involvement in comparison with limb muscle involvement.

Extended phenotype description and new molecular findings in late onset glycogen storage disease type II: a northern Italy population study and review of the literature

Glycogen storage disease type II (GSDII) is a lysosomal storage disorder caused by acid alpha-1,4-glucosidase deficiency and associated with recessive mutations in its coding gene GAA. Few studies have provided so far a detailed phenotypical characterization in late onset GSDII (LO-GSDII) patients. Genotype-phenotype correlation has been previously attempted with controversial results. We aim to provide an in-depth description of a cohort (n = 36) of LO-GSDII patients coming from the north of Italy and compare our population's findings to the literature. We performed a clinical record-based retrospective and prospective study of our patients. LO-GSDII in our cohort covers a large variability of phenotype including subtle clinical presentation and did not differ significantly from previous data. In all patients, molecular analysis disclosed GAA mutations, five of them being novel. To assess potential genotype-phenotype correlations we divided IVS1-32-13T>G heterozygous patients into two groups following the severity of the mutations on the second allele. Our patients harbouring "severe" mutations (n = 21) presented a strong tendency to have more severe phenotypes and more disability, more severe phenotypes and more disability, higher prevalence of assisted ventilation and a shorter time of evolution to show it. The determination of prognostic factors is mandatory in order to refine the accuracy of prognostic information, to develop follow-up strategy and, more importantly, to improve the decision algorithm for enzyme replacement therapy administration. The demonstration of genotype-phenotype correlations could help to reach this objective. Clinical assessment homogeneity is required to overcome limitations due to the lack of power of most studies.

Production of a functional human acid maltase in tobacco seeds: biochemical analysis, uptake by human GSDII cells, and in vivo studies in GAA knockout mice

Genetic deficiency of acid alpha glucosidase (GAA) results in glycogen storage disease type II (GSDII) or Pompe's disease. To investigate whether we could generate a functional recombinant human GAA enzyme (tobrhGAA) in tobacco seeds for future enzyme replacement therapy, we subcloned the human GAA cDNA into the plant expression plasmid-pBI101 under the control of the soybean β-conglycinin seed-specific promoter and biochemically analyzed the tobrhGAA. Tobacco seeds contain the metabolic machinery that is more compatible with mammalian glycosylation-phosphorylation and processing. We found the tobrhGAA to be enzymatically active was readily taken up by GSDII fibroblasts and in white blood cells from whole blood to reverse the defect. The tobrhGAA corrected the enzyme defect in tissues at 7 days after a single dose following intraperitoneal (IP) administration in GAA knockout (GAA(-/-)) mice. Additionally, we could purify the tobrhGAA since it bound tightly to the matrix of Sephadex G100 and can be eluted by competition with maltose. These data demonstrate indirectly that the tobrhGAA is fully functional, predominantly proteolytically cleaved and contains the minimal phosphorylation and mannose-6-phosphate residues essential for biological activity.

The French Pompe registry. Baseline characteristics of a cohort of 126 patients with adult Pompe disease

Pompe disease is a rare autosomal recessive muscle lysosomal glycogenosis, characterised by limb-girdle muscle weakness and frequent respiratory involvement. The French Pompe registry was created in 2004 with the initial aim of studying the natural history of French patients with adult Pompe disease. Since the marketing in 2006 of enzyme replacement therapy (alglucosidase alfa, Myozyme(®)), the French Pompe registry has also been used to prospectively gather the biological and clinical follow-up data of all adult patients currently treated in France. This report describes the main clinical and molecular features, at the time of inclusion in the French registry, of 126 patients followed up in 21 hospital-based neuromuscular or metabolic centres. Sixty-five men and 61 women have been included in the registry. Median age at inclusion was 49 years, and the median age at onset of progressive limb weakness was 35 years. Fifty-five percent of the patients were walking without assistance, 24% were using a stick or a walking frame, and 21% were using a wheelchair. Forty-six percent of the patients needed ventilatory assistance, which was non-invasive in 35% of the cases. When performed, muscle biopsies showed specific features of Pompe disease in less than two-thirds of the cases, confirming the importance of acid alpha-glucosidase enzymatic assessment to establish the diagnosis. Molecular analysis detected the common c.-32-13T>G mutation, in at least one allele, in 90% of patients. The French Pompe registry is so far the largest country-based prospective study of patients with Pompe disease, and further analysis will be performed to study the impact of enzyme replacement therapy on the progression of the disease.

Single nucleotide deletion of cqm1 gene results in the development of resistance to Bacillus sphaericus in Culex quinquefasciatus

The entomopathogen Bacillus sphaericus is one of the most effective biolarvicides used to control the Culex species of mosquito. The appearance of resistance in mosquitoes to this bacterium, however, remains a threat to its continuous use in integrated mosquito control programs. Previous work showed that the resistance to B. sphaericus in Culex colonies was associated with the absence of the 60-kDa binary toxin receptor (Cpm1/Cqm1), an alpha-glucosidase present in the larval midgut microvilli. In this work, we studied the molecular basis of the resistance developed by Culex quinquefasciatus to B. sphaericus C3-41. The cqm1 genes were cloned from susceptible (CqSL) and resistant (CqRL/C3-41) colonies, respectively. The sequence of the cDNA and genomic DNA derived from CqRL/C3-41 colony differed from that of CqSL one by a one-nucleotide deletion which resulted in a premature stop codon, leading to production of a truncated protein. Recombinant Cqm1S from the CqSL colony expressed in Escherichia coli specifically bound to the Bin toxin and had α-glucosidase activity, whereas the Cqm1R from the CqRL/C3-41 colony, with a deletion of three quarters of the receptor's C-terminal lost its α-glucosidase activity and could not bind to the binary toxin. Immunoblotting experiments showed that Cqm1 was undetectable in CqRL/C3-41 larvae, although the gene was correctly transcribed. Thus, the cqm1R represents a new allele in C. quinquefasciatus that confers resistance to B. sphaericus.

Pain in adult patients with Pompe disease: a cross-sectional survey

BACKGROUND

Pompe disease is a rare hereditary metabolic myopathy caused by a deficiency of acid-α-glucosidase. We investigated the presence and severity of pain and its interference with daily activities in a large group of adults with Pompe disease, who we compared with an age-matched control group.

METHODS

Data were collected in a cross-sectional survey in Germany and The Netherlands. Pain was assessed using the short-form brief pain inventory (BPI). Patients also completed the Short Form-36 item (SF-36v2), the Hospital Anxiety and Depression Scale (HADS) and the Rotterdam Handicap Scale (RHS).

RESULTS

Forty-five percent of the 124 adult Pompe patients reported having had pain in the previous 24h, against 27% of the 111 controls (p=0.004). The median pain severity score in Pompe patients reporting pain was 3.1 (on a scale from 0 to 10), indicating mild pain; against 2.6 amongst controls (p=0.06). The median score of pain interference with daily activities in patients who reported pain was 3.3, against 1.3 in controls (p=0.001). Relative to patients without pain, those with pain had lower RHS scores (p=0.02), lower SF-36 Physical and Mental component summary scores (p<0.001 and p=0.049), and higher levels of depression and anxiety (p=0.005 and p=0.003).

CONCLUSIONS

To date, this is one of the largest studies on pain in a specific neuromuscular disorder. Nearly one in two Pompe patients had experienced pain in the previous 24h. Although pain severity and its interference with daily life were mild, pain was related to a reduced quality of life, less participation in daily life, and greater depression and anxiety. Its management should therefore be seen as part of clinical practice involving Pompe patients.

[Clinical features and acid alpha-glucosidase gene mutation in 7 Chinese patients with glycogen storage disease type II]

OBJECTIVE

To explore the clinical features and acid alpha-glucosidase (GAA) gene mutations of Chinese patients with glycogen storage disease typeII(GSDII).

METHODS

Seven patients with GSDII were diagnosed by muscle pathology examination at Department of Neurology, Peking University First Hospital from 2003 to 2011. One patient with infant-onset presented development retardation, generalized muscle weakness, dyspnea, cardiomegaly and hepatomegaly. Six cases were of late-onset ranging from 1 to 29 years. Their main clinical features included progressive muscle weakness. Two patients developed respiratory insufficiency. Increased serum creatine kinase was detected in all of them. Electromyography studies showed myopathic (n = 5) and neuropathic (n = 1) changes. Muscle biopsies showed basophilic vacuoles in muscle fibers containing a large amounts of glycogen on electron microscopy. GAA gene mutation was detected by direct sequencing of polymerase chain reaction (PCR) product. Novel mutations were screened in 100 normal controls.

RESULTS

GAA gene mutations were found in all of them, including 10 point mutations and 1 frameshift deletion. Six mutations (p. P361L, p. P266S, p.R437C, p.R600C, p.W746S and p.W746*) have been reported before. And five novel mutations (p.R168Q, p.R168P, p.E521V, p.R594H and c.827_845del) were found in this study. None of these novel mutations were found in 100 normal controls except for p.R168Q mutation in two normal controls. p. P361L and p.W746* were detected in two unrelated GSDII patients while other mutations were carried by only one patient.

CONCLUSIONS

In our study, we found several novel GAA mutations in Chinese patients with GSDII. No hot spot mutation of GAA gene existed in our patient group. However, p. P266S, p. P361L and p.R437C might be associated with late-onset GSDII.

Antiviral therapies targeting host ER alpha-glucosidases: current status and future directions

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ER α-glucosidases are essential host factors for the morphogenesis of many enveloped viruses.

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Imino sugars are competitive inhibitors of the ER α-glucosidases I and II.

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Broad-spectrum antiviral efficacies of imino sugars have been demonstrated in vitro, and in vivo.

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Strategies for development of potent and specific ER α-glucosidase inhibitors have been proposed.

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Targeting glucosidase is promising for viral hemorrhagic fever and respiratory infections.

Endoplasmic reticulum (ER)-resident α-glucosidases I and II sequentially trim the three terminal glucose moieties on N-linked glycans attached to nascent glycoproteins. These reactions are the first steps of N-linked glycan processing and are essential for proper folding and function of many glycoproteins. Because most viral envelope glycoproteins contain N-linked glycans, inhibition of ER α-glucosidases with derivatives of 1-deoxynojirimycin (DNJ) or castanospermine (CAST), two well-studied pharmacophores of α-glucosidase inhibitors, efficiently disrupts the morphogenesis of a broad spectrum of enveloped viruses. Moreover, both DNJ and CAST derivatives have been demonstrated to prevent the death of mice infected with several distinct flaviviruses and filoviruses and suppress the multiplication of several other species of viruses in infected animals. N-Butyl derivative of DNJ (NB-DNJ) and 6 O-bytanoyl prodrug of CAST (Bu-CAST) have been evaluated in human clinical trials for their antiviral activities against human immunodeficiency virus and hepatitis C virus, and there is an ongoing trial of treating dengue patients with Bu-CAST. This article summarizes the current status of ER α-glucosidase-targeted antiviral therapy and proposes strategies for development of more efficacious and specific ER α-glucosidase inhibitors as broad-spectrum, drug resistance-refractory antiviral therapeutics. These host function-targeted, broad-spectrum antiviral agents do not rely on time-consuming etiologic diagnosis, and should therefore be particularly promising in the management of viral hemorrhagic fever and respiratory tract viral infections, medical conditions that can be caused by many different enveloped RNA viruses, with a short window for medical intervention.

Molecular cloning and characterization of the α-glucosidase II from Bombyx mori and Spodoptera frugiperda

The α-glucosidase II (GII) is a heterodimer of α- and β-subunits and important for N-glycosylation processing and quality control of nascent glycoproteins. Although high concentration of α-glucosidase inhibitors from mulberry leaves accumulate in silkworms (Bombyx mori) by feeding, silkworm does not show any toxic symptom against these inhibitors and N-glycosylation of recombinant proteins is not affected. We, therefore, hypothesized that silkworm GII is not sensitive to the α-glucosidase inhibitors from mulberry leaves. However, the genes for B. mori GII subunits have not yet been identified, and the protein has not been characterized. Therefore, we isolated the B. mori GII α- and β-subunit genes and the GII α-subunit gene of Spodoptera frugiperda, which does not feed on mulberry leaves. We used a baculovirus expression system to produce the recombinant GII subunits and identified their enzyme characteristics. The recombinant GII α-subunits of B. mori and S. frugiperda hydrolyzed p-nitrophenyl α-d-glucopyranoside (pNP-αGlc) but were inactive toward N-glycan. Although the B. mori GII β-subunit was not required for the hydrolysis of pNP-αGlc, a B. mori GII complex of the α- and β-subunits was required for N-glycan cleavage. As hypothesized, the B. mori GII α-subunit protein was less sensitive to α-glucosidase inhibitors than was the S. frugiperda GII α-subunit protein. Our observations suggest that the low sensitivity of GII contributes to the ability of B. mori to evade the toxic effect of α-glucosidase inhibitors from mulberry leaves.

Dysregulation of multiple facets of glycogen metabolism in a murine model of Pompe disease

Pompe disease, also known as glycogen storage disease (GSD) type II, is caused by deficiency of lysosomal acid α-glucosidase (GAA). The resulting glycogen accumulation causes a spectrum of disease severity ranging from a rapidly progressive course that is typically fatal by 1 to 2 years of age to a slower progressive course that causes significant morbidity and early mortality in children and adults. The aim of this study is to better understand the biochemical consequences of glycogen accumulation in the Pompe mouse. We evaluated glycogen metabolism in heart, triceps, quadriceps, and liver from wild type and several strains of GAA^−/− mice. Unexpectedly, we observed that lysosomal glycogen storage correlated with a robust increase in factors that normally promote glycogen biosynthesis. The GAA^−/− mouse strains were found to have elevated glycogen synthase (GS), glycogenin, hexokinase, and glucose-6-phosphate (G-6-P, the allosteric activator of GS). Treating GAA^−/− mice with recombinant human GAA (rhGAA) led to a dramatic reduction in the levels of glycogen, GS, glycogenin, and G-6-P. Lysosomal glycogen storage also correlated with a dysregulation of phosphorylase, which normally breaks down cytoplasmic glycogen. Analysis of phosphorylase activity confirmed a previous report that, although phosphorylase protein levels are identical in muscle lysates from wild type and GAA^−/− mice, phosphorylase activity is suppressed in the GAA^−/− mice in the absence of AMP. This reduction in phosphorylase activity likely exacerbates lysosomal glycogen accumulation. If the dysregulation in glycogen metabolism observed in the mouse model of Pompe disease also occurs in Pompe patients, it may contribute to the observed broad spectrum of disease severity.

Genome wide analysis of chromosomal alterations in oral squamous cell carcinomas revealed over expression of MGAM and ADAM9

Despite the advances in diagnosis and treatment of oral squamous cell carcinoma (OSCC), mortality and morbidity rates have not improved over the past decade. A major drawback in diagnosis and treatment of OSCC is the lack of knowledge relating to how genetic instability in oral cancer genomes affects oral carcinogenesis. Hence, the key aim of this study was to identify copy number alterations (CNAs) that may be cancer associated in OSCC using high-resolution array comparative genomic hybridization (aCGH). To our knowledge this is the first study to use ultra-high density aCGH microarrays to profile a large number of OSCC genomes (n = 46). The most frequently amplified CNAs were located on chromosome 11q11(52%), 2p22.3(52%), 1q21.3-q22(54%), 6p21.32(59%), 20p13(61%), 7q34(52% and 72%),8p11.23-p11.22(80%), 8q11.1-q24.4(54%), 9q13-q34.3(54%), 11q23.3-q25(57%); 14q21.3-q31.1(54%); 14q31.3-q32.33(57%), 20p13-p12.3(54%) and 20q11.21-q13.33(52%). The most frequently deleted chromosome region was located on 3q26.1 (54%). In order to verify the CNAs from aCGH using quantitative polymerase chain reaction (qPCR), the three top most amplified regions and their associated genes, namely ADAM5P (8p11.23-p11.22), MGAM (7q34) and SIRPB1 (20p13.1), were selected in this study. The ADAM5P locus was found to be amplified in 39 samples and deleted in one; MGAM (24 amplifications and 3 deletions); and SIRPB1 (12 amplifications, others undetermined). On the basis of putative cancer-related annotations, two genes, namely ADAM metallopeptidase domain 9 (ADAM9) and maltase-glucoamylase alpha-glucosidase (MGAM), that mapped to CNA regions were selected for further evaluation of their mRNA expression using reverse transcriptase qPCR. The over-expression of MGAM was confirmed with a 6.6 fold increase in expression at the mRNA level whereas the fold change in ADAM9 demonstrated a 1.6 fold increase. This study has identified significant regions in the OSCC genome that were amplified and resulted in consequent over-expression of the MGAM and ADAM9 genes that may be utilized as biological markers for OSCC.

Detection of a novel mutation in the GAA gene in an Iranian child with glycogen storage disease type II

Glycogen storage disease II (GSDII or Pompe disease, OMIM # 232300) is an autosomal recessive hereditary lysosomal disorder. Mutations in the GAA gene usually lead to reduced acid α-glucosidase (acid maltase, GAA, OMIM *606800, EC 3.1.26.2) activity, which results in impaired degradation and subsequent accumulation of glycogen within lysosomes. We present an Iranian boy, who was diagnosed with GSDII based upon clinical and biochemical findings. A single adenine insertion (insA) was detected at codon 693 that leads to a predicted premature stop codon at codon 736 in the GAA gene. The parents were heterozygous for the same change. According to the human genome mutation database (www.hgmd.org) and lecture reviews, the detected change is a novel mutation. We suppose that the discovered insertion in the GAA gene might lead to a reduced activity of the gene product. This assumption is in agreement with biochemical and clinical signs in the patient.

Three patients with glycogen storage disease type II and the mutational spectrum of GAA in Korean patients

BACKGROUND

Glycogen storage disease II (GSD II) is caused by a deficiency of acid alpha-1,4-glucosidase and mutations in the GAA gene encoding this enzyme which are responsible for the pathogenesis of GSD II. Our goal was to determine the mutational spectrum in the GAA gene in Korean patients with GSD II.

METHODS

Three patients with GSD II were recruited based on clinical and biochemical findings. Alpha-1,4-glucosidase activity was determined and the GAA gene sequence was analyzed by PCR and sequencing. We also collected information about the genotypes of Korean patients with GSD II from the medical literature.

RESULTS

We identified six mutant alleles among the three GSD II patients: c.875A>G, c.1156C>T, c.1316T>A, c.1857C>G, and c2407_2412del7. c.1156C>T (Q386*) is a novel mutation. A comprehensive review of the literature revealed that a total of 29 mutant alleles, including 15 different mutations (10 missense, 3 deletion, and 2 nonsense mutations), were previously identified in 15 Korean GSD II patients. c.1316T>A (p.M439K) and c.1857C>G (p.S619R) were the most common mutations and accounted for 36.6% of the total mutant alleles.

CONCLUSIONS

We identified three GSD II patients and investigated the mutational spectrum in GAA in Korean patients with GSD II. Our results indicate that common mutations in the GAA gene vary according to ethnic background.

Reconstruction of ancestral metabolic enzymes reveals molecular mechanisms underlying evolutionary innovation through gene duplication

Gene duplications are believed to facilitate evolutionary innovation. However, the mechanisms shaping the fate of duplicated genes remain heavily debated because the molecular processes and evolutionary forces involved are difficult to reconstruct. Here, we study a large family of fungal glucosidase genes that underwent several duplication events. We reconstruct all key ancestral enzymes and show that the very first preduplication enzyme was primarily active on maltose-like substrates, with trace activity for isomaltose-like sugars. Structural analysis and activity measurements on resurrected and present-day enzymes suggest that both activities cannot be fully optimized in a single enzyme. However, gene duplications repeatedly spawned daughter genes in which mutations optimized either isomaltase or maltase activity. Interestingly, similar shifts in enzyme activity were reached multiple times via different evolutionary routes. Together, our results provide a detailed picture of the molecular mechanisms that drove divergence of these duplicated enzymes and show that whereas the classic models of dosage, sub-, and neofunctionalization are helpful to conceptualize the implications of gene duplication, the three mechanisms co-occur and intertwine.

An apparent homozygous deletion in maltase-glucoamylase, a lesson in the evolution of SNP arrays

Single nucleotide polymorphism (SNP) arrays possess clinical potential due to their high throughput capacity, sensitivity and versatility. We used such an array to perform a genome-wide SNP analysis of a patient with a multi-system undiagnosed disease involving peripheral neuropathies and food intolerances. The patient had a homozygous deletion within the gene encoding maltase-glucoamylase (MGAM), an intestinal starch digestion enzyme, predicting absence of enzyme activity and potential starch indigestion. We then performed validation testing using a functional MGAM analysis that involved starch ingestion followed by measuring blood glucose and insulin levels as well as hydrogen breath levels. Gastrointestinal tissue was also obtained via endoscopy and immunohistochemical staining for intestinal MGAM was performed. Our results strongly suggest the presence and functioning of MGAM which disproved deficiency predictions based on SNP array analysis findings, classifying the deletion as a functional polymorphism. This study highlights a current clinical limitation of SNP arrays, i.e., distinguishing deleterious genomic alterations from misleading functional polymorphisms. We conclude that novel findings from SNP arrays should be clinically validated and published.

Phylogenomic relationships between amylolytic enzymes from 85 strains of fungi

Fungal amylolytic enzymes, including α-amylase, gluocoamylase and α-glucosidase, have been extensively exploited in diverse industrial applications such as high fructose syrup production, paper making, food processing and ethanol production. In this paper, amylolytic genes of 85 strains of fungi from the phyla Ascomycota, Basidiomycota, Chytridiomycota and Zygomycota were annotated on the genomic scale according to the classification of glycoside hydrolase (GH) from the Carbohydrate-Active enZymes (CAZy) Database. Comparisons of gene abundance in the fungi suggested that the repertoire of amylolytic genes adapted to their respective lifestyles. Amylolytic enzymes in family GH13 were divided into four distinct clades identified as heterologous α- amylases, eukaryotic α-amylases, bacterial and fungal α-amylases and GH13 α-glucosidases. Family GH15 had two branches, one for gluocoamylases, and the other with currently unknown function. GH31 α-glucosidases showed diverse branches consisting of neutral α-glucosidases, lysosomal acid α-glucosidases and a new clade phylogenetically related to the bacterial counterparts. Distribution of starch-binding domains in above fungal amylolytic enzymes was related to the enzyme source and phylogeny. Finally, likely scenarios for the evolution of amylolytic enzymes in fungi based on phylogenetic analyses were proposed. Our results provide new insights into evolutionary relationships among subgroups of fungal amylolytic enzymes and fungal evolutionary adaptation to ecological conditions.

Remarkably low fibroblast acid α-glucosidase activity in three adults with Pompe disease

INTRODUCTION

Most adults with Pompe disease are compound heterozygotes in which one acid α-glucosidase (GAA) allele harbors the c.-32-13T>G mutation, causing partial loss of GAA, and the other allele harbors a fully deleterious mutation. The fibroblast GAA activity in these patients is usually between 5% and 25% of the average in healthy individuals. In some adult patients, however, the fibroblast GAA activity is much lower and is in the range that is normally observed in classic-infantile Pompe disease. We investigated the genotype-phenotype correlation in three such adult patients and measured the GAA activity as well as the glycogen content in muscle and fibroblasts in order to better understand the clinical course.

METHODS

DNA was sequenced and GAA activity and glycogen content were measured in leukocytes, fibroblasts and muscle. Muscle biopsies were microscopically analyzed and the biosynthesis of GAA in fibroblasts was analyzed by immunoblotting. GAA activity and glycogen content in fibroblasts and muscle tissue in healthy controls, adult patients with Pompe disease and classic-infantile patients were compared with those of the three index patients.

RESULTS

One patient had genotype c.525delT/c.671G>A (r.0/p.Arg224Gln). Two affected brothers had genotype c.569G>A/c.1447G>A (p.Arg190His/p.Gly483Arg). In all three cases the GAA activity and the glycogen content in fibroblasts were within the same range as in classic-infantile Pompe disease, but the activity and glycogen content in muscle were both within the adult range. In fibroblasts, the first step of GAA synthesis appeared unaffected but lysosomal forms of GAA were not detectable with immunoblotting.

CONCLUSION

Some adult patients with mutations other than c.-32-13T>G can have very low GAA activity in fibroblasts but express higher activity in muscle and store less glycogen in muscle than patients with classic-infantile Pompe disease. This might explain why these patients have a slowly progressive course of Pompe disease.

Expression and purification of two Family GH31 α-glucosidases from Bacteroides thetaiotaomicron

Microorganisms in the human gut outnumber human cells by a factor of 10. These microbes have been shown to have relevance to the human immune, nutrition and metabolic systems. A dominant symbiont of this environment is Bacteroides thetaiotaomicron which is characterized as being involved in degrading non-digestible plant polysaccharides. This organism's genome is highly enriched in genes predicted to be involved in the hydrolysis of various glycans. Presented here is a comparative functional analysis of two α-glucosidases (designated BT_0339 and BT_3299), Family 31 Glycoside Hydrolases from B. thetaiotaomicron. The purpose of this research is to explore the contributions these enzymes may have to human nutrition and specifically starch digestion. Expression of both α-glucosidases in pET-29a expression vector resulted in high levels of expressed protein in the soluble fraction. Two-step purification allowed for the isolation of the enzymes of interest in significant yield and fractions were observed to be homogenous. Both enzymes demonstrated activity on maltose, isomaltose and malto-oligosaccharide substrates and low level of activity on lactose and sucrose. Enzymatic kinetics revealed these enzymes both preferentially cleave the α1-6 linkage in comparison to the expected α1-4 and specifically favor maltose-derived substrates of longer length. The flexible hydrolytic capabilities of BT_0339 and BT_3299 reveal the ability of this bacterium to maintain its dominant position in its environment by utilizing an array of substrates. Specifically, these enzymes demonstrate an important aspect of this organism's contribution to starch digestion in the distal gut and the overall energy intake of humans.

Diagnosing lysosomal storage disorders: Pompe disease

Pompe disease is a lysosomal storage disorder caused by a deficiency of acid alpha glucosidase (GAA). Diagnosis of Pompe disease is typically based on an enzyme analysis of blood or tissues, such as fibroblasts, followed by confirmation through molecular testing. The advent of fluorometric and mass spectrometry methods for enzyme analysis in dried blood spots (DBS) has simplified the diagnostic approach for Pompe disease, facilitating high-throughput screening of at-risk populations and newborn infants. The following unit will provide the detailed analytical protocol for measurement of GAA activity in DBS using tandem mass spectrometry.