Glycogen Storage Disease 1b Research Articles

A different isoform of the transport protein mutated in the glycogen storage disease 1b is expressed in brain

There are differences in the kinetic properties of the liver and brain microsomal glucose-6-phosphate transport systems suggesting the possibility of tissue specific isoforms. The availability of a human liver cDNA sequence which is mutated in patients with deficiencies of liver microsomal glucose-6-phosphate transport (glycogen storage disease 1b) made it possible to determine if a brain isoform exists. Northern blots of liver and brain RNA revealed that the mRNA of the brain form is slightly longer than the liver one. Isolation and sequencing of the respective human brain cDNA revealed that the brain protein has an additional 22 amino acid sequence.

Liver microsomal transport of glucose-6-phosphate, glucose, and phosphate in type 1 glycogen storage disease.

The transport of glucose-6-phosphate (G6P), glucose, and orthophosphate into liver microsomes, isolated from six patients with various subtypes of type 1 glycogen storage disease (GSD), was measured using a light-scattering method. We found that G6P, glucose, and phosphate could all cross the microsomal membrane, in four cases of type 1a GSD. In contrast, liver microsomal transport of G6P and phosphate was deficient in the GSD 1b and 1c patients, respectively. These results support the involvement of multiple proteins (and genes) in GSD type 1. The results obtained with the light-scattering method are in accordance with conventional kinetic analysis of the microsomal glucose-6-phosphatase system. Therefore, this technique could be used to directly diagnose type 1b and 1c GSD.

Interferon-gamma corrects the respiratory burst defect in vitro in monocyte-derived macrophages from glycogen storage disease type 1b patients.

Glycogen storage disease (GSD) type 1b is accompanied by decreased respiratory burst activity in peripheral blood phagocytic cells (i.e. monocytes and neutrophils). To elucidate whether this depressed respiratory burst was due to an intrinsic defect of phagocytic cells or due in part to in vivo host factors, we examined superoxide anion (O2-) production in monocytes from five GSD 1b patients cultured 9 d in vitro to allow for differentiation into macrophages (MDM). O2- production in MDM was measured in response to concanavalin A, fMet-Leu-Phe, and phorbol myristate acetate (PMA) stimulation. GSD 1b MDM had significantly depressed O2- generation with fMet-Leu-Phe and concanavalin A stimulation; however, unlike peripheral blood monocytes, GSD 1b MDM responded to PMA stimulation with O2- production comparable to healthy control donors. The cytokine interferon-gamma (IFN-gamma) has been shown to enhance O2- production in MDM. When GSD 1b MDM were cultured in the presence of IFN-gamma (1 x 10(5) U/L), O2- production in response to fMet-Leu-Phe, concanavalin A, and PMA was enhanced to rates similar to those of control MDM cultured in the presence of IFN-gamma. Thus, the respiratory burst defect observed in circulating phagocytic cells is also present in vitro in cultured GSD 1b MDM. However, in contrast to circulating phagocytic cells, depressed O2- production in GSD 1b MDM is selective to receptor-mediated activation, but not to PMA stimulation. This defect is correctable after short-term treatment with IFN-gamma, suggesting a role for IFN-gamma in treating the phagocytic defect in this disease.

Deficient glucose phosphorylation as a possible common denominator and its relation to abnormal leucocyte function, in glycogen storage disease 1b patients

Patients with glycogen storage disease (GSD) 1b suffer from recurrent bacterial infections related to neutropenia and impairment of neutrophil functions. One of these functions is the oxidative burst activity which is initiated by NADPH oxidase and depends on the availability of glucose. This activity was markedly reduced in the patient's intact neutrophils when either N-formyl-methionyl-leucyl-phenylalanine (fMLP), or phorbol myristate acetate were used as stimulants. In disrupted GSD 1b polymorphonuclear leucocytes (PMNs), in the presence of exogenous NADPH, this activity was within the normal range. Degranulation, which is calcium dependent but glucose independent, was not significantly different in neutrophils from the patients as compared to controls. Resting cytosolic calcium concentration was indistinguishable from controls. Activation with 10(-7) M fMLP, in the presence or absence of glucose, triggered a prompt and rapid elevation of cytosolic calcium both in the control and the patients' cells. We have previously shown that hexose monophosphate (HMP) shunt activity and glycolytic rate were found to be lower by 70% in intact PMN cells of the patients compared with controls. These activities were normal in disrupted neutrophils. The uptake of the non-metabolized glucose analogues 2-deoxyglucose (2-DOG) and 3-O-Methylglucose (3-OMG) into PMN of GSD 1b patients was studied. 2-DOG is phosphorylated within the cells, thus its uptake rate reflects hexose transport at low concentrations, as long as phosphorylation is not rate limiting. Under those conditions (5 microM 2-DOG) transport was found to be similar to controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Impairment of calcium mobilization in phagocytic cells in glycogen storage disease type 1b.

Patients with glycogen storage disease (GSD) type 1b, in contrast to patients with GSD 1a, are susceptible to recurrent bacterial infections suggesting defective phagocytic function. We have demonstrated a selective defect in respiratory burst activity but not in degranulation by phagocytic cells in GSD 1b but not in GSD 1a. The respiratory burst abnormality in phagocytic cells from GSD 1b patients was associated with impaired calcium mobilization, whereas these processes were normal in GSD 1a patients. Therefore, the alteration in calcium mobilization was an indication of a signalling defect in phagocytic cells from GSD 1b. However, calcium mobilization was normal in lymphocytes, indicating that defective calcium mobilization was not a global finding in circulating leukocytes, but was specific to phagocytic cells. Calcium mobilization in response to ionomycin was reduced suggesting decreased calcium stores in GSD 1b neutrophils. Therefore, altered phagocytic cell function in GSD 1b patients appears to be associated with diminished calcium mobilization and defective calcium stores. This defective calcium signalling was associated with a selective defect in respiratory burst activity but not degranulation.

Advances in pathophysiology, diagnosis, and treatment of neutrophil defects

Recent literature relevant to neutrophil defects in pediatric patients spans a wide range of interests. Significant new observations on the molecular pathology, pathogenesis, prenatal diagnosis and therapy, as well as thorough clinical reviews of neutrophil defects appeared during the past year. Diverse types of congenital neutropenias are documented to respond to granulocyte-colony stimulating factor and granulocyte-macrophage colony-stimulating factor and differences in responses may yield insight into the pathogenesis of chronic benign neutropenia, Kostmann's agranulocytosis, and the neutropenia of glycogen storage disease 1b. Leukocyte adhesion deficiency can be diagnosed in utero; however, the assays are crude and do not yet take advantage of the rapidly increasing knowledge of transcriptional or translational abnormalities in CD11b expression. In chronic granulomatous disease (CGD), rapidly increasing knowledge of the molecular basis of gene defects in X-linked CGD led to identification of point mutations as well as gross deletions of the gp91phox gene that cause CGD. Furthermore, advances in the therapy of CGD with interferon-7 are now paired with suggestions that increase in nitroblue tetrazolium reduction by monocytes may underlie the efficacy of interferon-y in CGD. Recently improved methods of analyzing cytoskeletal dynamics in the neutrophil has led to the description of a novel neutrophil defect with defective motility and defective actin polymerization, and studies of acquired neutrophil defects point to the importance of transforming growth factor (3 and cytokines as modulators of defective neutrophil function in several immunoregulatory defects associated with increased susceptibility to bacterial infection.

Impaired metabolic function and signaling defects in phagocytic cells in glycogen storage disease type 1b.

Patients with glycogen storage disease (GSD) type 1b (1b), in contrast to patients with GSD type 1a (1a), are susceptible to recurrent bacterial infections suggesting an impairment in their immune system. In this study, phagocytic cell (neutrophil and monocyte) respiratory burst activity, as measured by superoxide anion generation, oxygen consumption, and hexose monophosphate shunt activity, was markedly reduced in both neutrophils and monocytes from GSD 1b patients as compared with either GSD 1a patients or healthy adult control cells. Degranulation, unlike respiratory burst activity, was not significantly different in neutrophils from GSD 1b patients as compared with controls. Both neutrophils and monocytes from GSD 1b patients showed decreased ability to elevate cytosolic calcium in response to the chemotactic peptide f-Met-Leu-Phe. In addition, calcium mobilization in response to ionomycin was also attenuated suggesting decreased calcium stores. Thus, reduced phagocytic cell function in GSD 1b is associated with diminished calcium mobilization and defective calcium stores. Defective calcium signaling is associated with a selective defect in respiratory burst activity but not degranulation.