A new D-galactose treatment monitoring index for PGM1-CDG.

Phosphoglucomutase 1 (PGM1) catalyzes the interconversion of glucose-6-phosphate to glucose-1-phosphate and is a key enzyme of glycolysis, glycogenesis, and glycogenolysis. PGM1 deficiency (OMIM: 614921) was initially defined as a glycogen storage disorder (type XIV), and later re-classified as a PGM1-congenital disorder of glycosylation (PGM1-CDG). Serum transferrin (Tf) glycan isoform analysis by liquid chromatography-mass spectrometry (LC-MS) is used as a primary diagnostic screen tool, and reveals a very unique CDG profile described as a mixture of CDG-type I and CDG-type II patterns. Oral d-galactose supplementation shows significant clinical and metabolic improvements, which are indicated by the Tf glycan isoform normalization over time in patients with PGM1-CDG. Thus, there is a need for biomarkers to guide d-galactose dosage in patients in order to maintain effective and safe drug levels. Here, we present a simplified algorithm called PGM1-CDG Treatment Monitoring Index (PGM1-TMI) for assessing the response of PGM1-CDG patients to d-galactose supplementation. For our single-center cohort of 16 PGM1-CDG patients, the Tf glycan profile analysis provided the biochemical diagnosis in all of them. In addition, the PGM1-TMI was reduced in PGM1-CDG patients under d-galactose supplementation as compared with their corresponding values before treatment, indicating that glycosylation proceeds towards normalization. PGM1-TMI allows tracking Tf glycan isoform normalization over time when the patients are on d-galactose supplementation.

International consensus guidelines for phosphoglucomutase 1 deficiency (PGM1-CDG): Diagnosis, follow-up, and management.

Phosphoglucomutase 1 (PGM1) deficiency is a rare genetic disorder that affects glycogen metabolism, glycolysis, and protein glycosylation. Previously known as GSD XIV, it was recently reclassified as a congenital disorder of glycosylation, PGM1-CDG. PGM1-CDG usually manifests as a multisystem disease. Most patients present as infants with cleft palate, liver function abnormalities and hypoglycemia, but some patients present in adulthood with isolated muscle involvement. Some patients develop life-threatening cardiomyopathy. Unlike most other CDG, PGM1-CDG has an effective treatment option, d-galactose, which has been shown to improve many of the patients' symptoms. Therefore, early diagnosis and initiation of treatment for PGM1-CDG patients are crucial decisions. In this article, our group of international experts suggests diagnostic, follow-up, and management guidelines for PGM1-CDG. These guidelines are based on the best available evidence-based data and experts' opinions aiming to provide a practical resource for health care providers to facilitate successful diagnosis and optimal management of PGM1-CDG patients.

Links between autophagy and disorders of glycogen metabolism - Perspectives on pathogenesis and possible treatments.

The glycogen storage diseases are a group of inherited metabolic disorders that are characterized by specific enzymatic defects involving the synthesis or degradation of glycogen. Each disorder presents with a set of symptoms that are due to the underlying enzyme deficiency and the particular tissues that are affected. Autophagy is a process by which cells degrade and recycle unneeded or damaged intracellular components such as lipids, glycogen, and damaged mitochondria. Recent studies showed that several of the glycogen storage disorders have abnormal autophagy which can disturb normal cellular metabolism and/or mitochondrial function. Here, we provide a clinical overview of the glycogen storage disorders, a brief description of autophagy, and the known links between specific glycogen storage disorders and autophagy.

Antibody-Mediated Enzyme Therapeutics and Applications in Glycogen Storage Diseases.

The use of antibodies as targeting molecules or cell-penetrating tools has emerged at the forefront of pharmaceutical research. Antibody-directed therapies in the form of antibody-drug conjugates, immune modulators, and antibody-directed enzyme prodrugs have been most extensively utilized as hematological, rheumatological, and oncological therapies, but recent developments are identifying additional applications of antibody-mediated delivery systems. A novel application of this technology is for the treatment of glycogen storage disorders (GSDs) via an antibody-enzyme fusion (AEF) platform to penetrate cells and deliver an enzyme to the cytoplasm, nucleus, and/or other organelles. Exciting developments are currently underway for AEFs in the treatment of the GSDs Pompe disease and Lafora disease (LD). Antibody-based therapies are quickly becoming an integral part of modern disease therapeutics.

Guaiacol as a drug candidate for treating adult polyglucosan body disease.

Adult polyglucosan body disease (APBD) is a late-onset disease caused by intracellular accumulation of polyglucosan bodies, formed due to glycogen-branching enzyme (GBE) deficiency. To find a treatment for APBD, we screened 1,700 FDA-approved compounds in fibroblasts derived from APBD-modeling GBE1-knockin mice. Capitalizing on fluorescent periodic acid-Schiff reagent, which interacts with polyglucosans in the cell, this screen discovered that the flavoring agent guaiacol can lower polyglucosans, a result also confirmed in APBD patient fibroblasts. Biochemical assays showed that guaiacol lowers basal and glucose 6-phosphate-stimulated glycogen synthase (GYS) activity. Guaiacol also increased inactivating GYS1 phosphorylation and phosphorylation of the master activator of catabolism, AMP-dependent protein kinase. Guaiacol treatment in the APBD mouse model rescued grip strength and shorter lifespan. These treatments had no adverse effects except making the mice slightly hyperglycemic, possibly due to the reduced liver glycogen levels. In addition, treatment corrected penile prolapse in aged GBE1-knockin mice. Guaiacol's curative effects can be explained by its reduction of polyglucosans in peripheral nerve, liver, and heart, despite a short half-life of up to 60 minutes in most tissues. Our results form the basis to use guaiacol as a treatment and prepare for the clinical trials in APBD.

Pulmonary interstitial glycogenosis: Diagnostic evaluation and clinical course.

OBJECTIVES: We sought to describe the phenotype for patients with P.I.G. including presentation, evaluation, cardiac co-morbidities, high resolution computed tomography findings, and outcomes. METHODS: With institutional review board approval, we performed a retrospective review of patients with biopsy-proven P.I.G. Biopsies, high resolution chest computed tomography, and cardiac evaluations were reviewed and characterized by experts in each field. RESULTS: Sixty-two percent of the patients were male. The median gestational age was 37 weeks (range 27-40). The median age at biopsy was 1.6 months (range 0.3-6 months). Structural heart disease was present in 63% of patients. Pulmonary hypertension (diagnosed by echocardiogram and/or cardiac catheterization) was noted in 38% of patients. Alveolar simplification was present in 79% of patients. Fifty percent of available biopsies revealed patchy disease. An increase in age at biopsy was associated with patchy (vs diffuse) disease. Ninety-two percent of patients were treated with systemic corticosteroids. Median age at last follow-up was 1234 days with a range of 37 days to 15 years. At the time of last follow-up, 12 patients were off all support, eight were on supplemental oxygen, two were mechanically ventilated, one underwent lung transplantation, and one died. CT findings commonly included ground glass opacities (86%) and cystic change (50%). CONCLUSIONS: The P.I.G. phenotype has not been comprehensively described, and poor recognition and misconceptions about P.I.G. persist. P.I.G. is a disease that presents in early infancy, requires significant medical intervention, and frequently is seen in association with alveolar simplification and/or cardiovascular disease. CT findings include ground glass opacities and cysts. Patients should be monitored for pulmonary hypertension. Without life-threatening comorbidities, many patients do well over time, although respiratory symptoms may persist into adolescence.

Pulmonary interstitial glycogenosis - A systematic analysis of new cases.

BACKGROUND: Pulmonary interstitial glycogenosis (PIG) is a rare paediatric interstitial lung disease of unknown cause. The diagnosis can only be made by lung biopsy. Less than 100 cases have been reported. Clinical features, treatment and outcomes have rarely been assessed systematically in decent cohorts of patients. METHODS: In this retrospective multicentre study, the clinical presentation, radiologic findings, pattern of lung biopsy, extrapulmonary comorbidities, treatment and outcome of eleven children with PIG were collected systematically. RESULTS: 10/11 children presented with respiratory distress immediatly after birth and 8/11 needed invasive ventilation. In 8/11 children extrapulmonary comorbidities were present, congenital heart defects being the most common. 7/11 children received systemic glucocorticoids and of these four showed a clear favorable response. During a median follow-up of 3.0 years (range 0.42-12.0) one child died, while 10 patients improved. Chest CT-scans showed ground-glass opacities (7/10), consolidations (6/10), linear opacities (5/10) and mosaic attenuation (4/10) without uniform pattern. Besides interstitial thickening related to undifferentiated glycogen positive mesenchymal cells all tissue samples showed growth abnormalities with reduced alveolarization. CONCLUSIONS: PIG is associated with alveolar growth abnormalities and has to be considered in all newborns with unexplained respiratory distress. Apparent treatment benefit of glucocorticosteroids needs to be evaluated systematically.

A double-blind, placebo-controlled trial of triheptanoin in adult polyglucosan body disease and open-label, long-term outcome.

BACKGROUND: Adult polyglucosan body disease (APBD) is a progressive neurometabolic disorder caused by a deficiency of glycogen branching enzyme. We tested the efficacy of triheptanoin as a therapy for patients with APBD based on the hypothesis that decreased glycogen degradation leads to brain energy deficit. METHODS AND RESULTS: This was a two-site, randomized crossover trial of 23 patients (age 35-73 years; 63% men) who received triheptanoin or vegetable oil as placebo. The trial took place over 1 year and was followed by a 4-year open-label phase. Generalized linear mixed models were used to analyze this study. At baseline, using the 6-min walk test, patients could walk a mean of 389 ± 164 m (range 95-672; n = 19), highlighting the great clinical heterogeneity of our cohort. The overall mean difference between patients on triheptanoin versus placebo was 6 m; 95% confidence interval (CI) -11 to 22; p = 0.50. Motion capture gait analysis, gait quality, and stair climbing showed no consistent direction of change. All secondary endpoints were statistically nonsignificant after false discovery rate adjustment. Triheptanoin was safe and generally well tolerated. During the open-label phase of the study, the most affected patients at baseline kept deteriorating while mildly disabled patients remained notably stable up to 4 years. CONCLUSIONS: We cannot conclude that triheptanoin was effective in the treatment of APBD over a 6-month period, but we found it had a good safety profile. This study also emphasizes the difficulty of conducting trials in very rare diseases presenting with a wide clinical heterogeneity. ClinicalTrials.gov Identifier: NCT00947960.

A novel image-based high-throughput screening assay discovers therapeutic candidates for adult polyglucosan body disease.

Glycogen storage disorders (GSDs) are caused by excessive accumulation of glycogen. Some GSDs [adult polyglucosan (PG) body disease (APBD), and Tarui and Lafora diseases] are caused by intracellular accumulation of insoluble inclusions, called PG bodies (PBs), which are chiefly composed of malconstructed glycogen. We developed an APBD patient skin fibroblast cell-based assay for PB identification, where the bodies are identified as amylase-resistant periodic acid-Schiff's-stained structures, and quantified. We screened the DIVERSet CL 10 084 compound library using this assay in high-throughput format and discovered 11 dose-dependent and 8 non-dose-dependent PB-reducing hits. Approximately 70% of the hits appear to act through reducing glycogen synthase (GS) activity, which can elongate glycogen chains and presumably promote PB generation. Some of these GS inhibiting hits were also computationally predicted to be similar to drugs interacting with the GS activator protein phosphatase 1. Our work paves the way to discovering medications for the treatment of PB-involving GSD, which are extremely severe or fatal disorders.

Glucogenosis hepática diabética: un nuevo reto diagnóstico / Hepatic glycogenosis: a diagnostic challenge

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Oral D-galactose supplementation in PGM1-CDG.

PurposePhosphoglucomutase-1 deficiency is a subtype of congenital disorders of glycosylation (PGM1-CDG). Previous casereports in PGM1-CDG patients receiving oral D-galactose (D-gal) showed clinical improvement. So far no systematic in vitro and clinical studies have assessed safety and benefits of D-gal supplementation. In a prospective pilot study, we evaluated the effects of oral D-gal in nine patients.MethodsD-gal supplementation was increased to 1.5 g/kg/day (maximum 50 g/day) in three increments over 18 weeks. Laboratory studies were performed before and during treatment to monitor safety and effect on serum transferrin-glycosylation, coagulation, and liver and endocrine function. Additionally, the effect of D-gal on cellular glycosylation was characterized in vitro.ResultsEight patients were compliant with D-gal supplementation. No adverse effects were reported. Abnormal baseline results (alanine transaminase, aspartate transaminase, activated partial thromboplastin time) improved or normalized already using 1 g/kg/day D-gal. Antithrombin-III levels and transferrin-glycosylation showed significant improvement, and increase in galactosylation and whole glycan content. In vitro studies before treatment showed N-glycan hyposialylation, altered O-linked glycans, abnormal lipid-linked oligosaccharide profile, and abnormal nucleotide sugars in patient fibroblasts. Most cellular abnormalities improved or normalized following D-gal treatment. D-gal increased both UDP-Glc and UDP-Gal levels and improved lipid-linked oligosaccharide fractions in concert with improved glycosylation in PGM1-CDG.ConclusionOral D-gal supplementation is a safe and effective treatment for PGM1-CDG in this pilot study. Transferrin glycosylation and ATIII levels were useful trial end points. Larger, longer-duration trials are ongoing.

Hepatic glycogenosis: a diagnostic challenge.

Recently, several cases of hepatic glycogenosis (HG) have been reported. García-Suárez et al. described a young female patient with poorly controlled type 1 diabetes, right upper quadrant pain and elevated serum transaminases and GGT. After other causes of liver disease were excluded and a liver biopsy was performed, the patient was diagnosed with HG. HG is rare and can be misdiagnosed as steatohepatitis. To date, less than 20 cases have been reported in adults.

Triacylglycerol mimetics regulate membrane interactions of glycogen branching enzyme: implications for therapy.

Adult polyglucosan body disease (APBD) is a neurological disorder characterized by adult-onset neurogenic bladder, spasticity, weakness, and sensory loss. The disease is caused by aberrant glycogen branching enzyme (GBE) (GBE1Y329S) yielding less branched, globular, and soluble glycogen, which tends to aggregate. We explore here whether, despite being a soluble enzyme, GBE1 activity is regulated by protein-membrane interactions. Because soluble proteins can contact a wide variety of cell membranes, we investigated the interactions of purified WT and GBE1Y329S proteins with different types of model membranes (liposomes). Interestingly, both triheptanoin and some triacylglycerol mimetics (TGMs) we have designed (TGM0 and TGM5) markedly enhance GBE1Y329S activity, possibly enough for reversing APBD symptoms. We show that the GBE1Y329S mutation exposes a hydrophobic amino acid stretch, which can either stabilize and enhance or alternatively, reduce the enzyme activity via alteration of protein-membrane interactions. Additionally, we found that WT, but not Y329S, GBE1 activity is modulated by Ca2+ and phosphatidylserine, probably associated with GBE1-mediated regulation of energy consumption and storage. The thermal stabilization and increase in GBE1Y329S activity induced by TGM5 and its omega-3 oil structure suggest that this molecule has a considerable therapeutic potential for treating APBD.

PGM1 deficiency: Substrate use during exercise and effect of treatment with galactose.

Mutations in PGM1 (phosphoglucomutase 1) cause Glycogen Storage Disease type XIV, which is also a congenital disorder of protein N-glycosylation. It presents throughout life as myopathy with additional systemic symptoms. We report the effect of oral galactose treatment during five months in a patient with biochemically and genetically confirmed PGM1 deficiency. The 12-minute-walking distance increased by 225 m (65%) and transferrin glycosylation was restored to near-normal levels. The exercise assessments showed a severe exercise intolerance due to a block in skeletal muscle glycogenolytic capacity and that galactose treatment tended to normalize skeletal muscle substrate use from fat to carbohydrates during exercise.

Alglucosidase alfa enzyme replacement therapy as a therapeutic approach for a patient presenting with a PRKAG2 mutation.

OBJECTIVE: PRKAG2 syndrome, an autosomal dominant disorder, is characterized by severe infantile hypertrophic cardiomyopathy and heart rhythm disturbances to cases with a later presentation and a spectrum of manifestations including cardiac manifestations, myopathy and seizures. The cardiac features of PRKAG2 resemble the cardiac manifestations of Pompe disease. We present a patient who was initially diagnosed with Pompe disease and treated with alglucosidase-alfa enzyme replacement therapy (ERT); however, he was eventually diagnosed to carrying a PRKAG2 pathogenic gene mutation; he did not have Pompe disease instead he was a carrier for the common adult leaky splice site mutation in the GAA gene. CASE REPORT: At 2.5months, the patient had hypotonia/generalized muscle weakness, a diagnosis of non-classic infantile Pompe disease was made based on low acid alpha-glucosidase activity and the patient started on ERT at 11months. However, 1month later, the patient began to have seizures. As the patient's medical history was somewhat unusual for infantile Pompe disease, further evaluation was initiated and included a glycogen storage disease sequencing panel which showed that the patient had a pathogenic mutation in PRKAG2 which had been reported previously. ERT was discontinued and patient had a progression of motor deficits. ERT was reinitiated by the treating physician, and a clinical benefit was noted. CONCLUSION: This report outlines the benefits of ERT with alglucosidase alfa in a patient with PRKAG2 syndrome, the decline in his condition when the ERT infusions were discontinued, and the significant positive response when ERT was reinitiated.

The structure of brain glycogen phosphorylase-from allosteric regulation mechanisms to clinical perspectives.

Glycogen phosphorylase (GP) is the key enzyme that regulates glycogen mobilization in cells. GP is a complex allosteric enzyme that comprises a family of three isozymes: muscle GP (mGP), liver GP (lGP), and brain GP (bGP). Although the three isozymes display high similarity and catalyze the same reaction, they differ in their sensitivity to the allosteric activator adenosine monophosphate (AMP). Moreover, inactivating mutations in mGP and lGP have been known to be associated with glycogen storage diseases (McArdle and Hers disease, respectively). The determination, decades ago, of the structure of mGP and lGP have allowed to better understand the allosteric regulation of these two isoforms and the development of specific inhibitors. Despite its important role in brain glycogen metabolism, the structure of the brain GP had remained elusive. Here, we provide an overview of the human brain GP structure and its relationship with the two other members of this key family of the metabolic enzymes. We also summarize how this structure provides valuable information to understand the regulation of bGP and to design specific ligands of potential pharmacological interest.

Structural basis of glycogen branching enzyme deficiency and pharmacologic rescue by rational peptide design.

Glycogen branching enzyme 1 (GBE1) plays an essential role in glycogen biosynthesis by generating α-1,6-glucosidic branches from α-1,4-linked glucose chains, to increase solubility of the glycogen polymer. Mutations in the GBE1 gene lead to the heterogeneous early-onset glycogen storage disorder type IV (GSDIV) or the late-onset adult polyglucosan body disease (APBD). To better understand this essential enzyme, we crystallized human GBE1 in the apo form, and in complex with a tetra- or hepta-saccharide. The GBE1 structure reveals a conserved amylase core that houses the active centre for the branching reaction and harbours almost all GSDIV and APBD mutations. A non-catalytic binding cleft, proximal to the site of the common APBD mutation p.Y329S, was found to bind the tetra- and hepta-saccharides and may represent a higher-affinity site employed to anchor the complex glycogen substrate for the branching reaction. Expression of recombinant GBE1-p.Y329S resulted in drastically reduced protein yield and solubility compared with wild type, suggesting this disease allele causes protein misfolding and may be amenable to small molecule stabilization. To explore this, we generated a structural model of GBE1-p.Y329S and designed peptides ab initio to stabilize the mutation. As proof-of-principle, we evaluated treatment of one tetra-peptide, Leu-Thr-Lys-Glu, in APBD patient cells. We demonstrate intracellular transport of this peptide, its binding and stabilization of GBE1-p.Y329S, and 2-fold increased mutant enzymatic activity compared with untreated patient cells. Together, our data provide the rationale and starting point for the screening of small molecule chaperones, which could become novel therapies for this disease.

An infant with pulmonary interstitial glycogenosis: clinical improvement is associated with improvement in the pulmonary diffusion capacity.

Pulmonary interstitial glycogenosis (PIG) is an idiopathic interstitial lung disease of infants. The underlying pulmonary pathophysiology of PIG has not been well characterized. Herein we report a term-gestation infant who presented with persistent tachypnea and hypoxia. A chest CT scan demonstrated a diffuse ground glass appearance and lung biopsy demonstrated increased alveolar septae cellularity with glycogen-containing cells, consistent with a diagnosis of PIG. At 3 months of age, pulmonary function testing included: pre- and post-bronchodilator forced expiratory flows using the raised-volume technique and the ratio of pulmonary diffusing capacity for carbon monoxide to alveolar volume (DLCO /VA ). He was prescribed 5 days of oral prednisolone (2mg/kg/day) and pulmonary function testing (PFT) was repeated at 5, 13, and 20 months of age. Initial PFTs demonstrated reduced forced vital capacity (FVC: Z-score = -2.36) and an increased ratio of forced expiratory volume in 0.5 sec to FVC (FEV0.5/FVC: Z-score = 1.15) with no significant change following an inhaled bronchodilator. There was also a marked reduction in DLCO /VA (Z-score = -4.74) compared to age-matched controls. Follow-up demonstrated progressive clinical improvement as well as an increase in Z-FVC and normalization of DLCO /VA . Our in vivo physiological findings are consistent with previous reports that symptom resolution correlated with histological thinning of the alveolar septae upon repeat lung biopsy. The restrictive lung disease we observed is consistent with expected reduced compliance of an alveolar interstitial lung process like PIG, whereas the absence of a reduction in FEV0.5/FVC confirms the absence of obstructive airway disease.