Glycogen storage disease type 1b: microsomal glucose-6-phosphatase system in two patients with different clinical findings

Glycogen storage diseases: New perspectives

Glycogen storage diseases (GSD) are inherited metabolic disorders of glycogen metabolism. Different hormones, including insulin, glucagon, and cortisol regulate the relationship of glycolysis, gluconeogenesis and glycogen synthesis. The overall GSD incidence is estimated 1 case per 20000-43000 live births. There are over 12 types and they are classified based on the enzyme deficiency and the affected tissue. Disorders of glycogen degradation may affect primarily the liver, the muscle, or both. Type Ia involves the liver, kidney and intestine (and Ib also leukocytes), and the clinical manifestations are hepatomegaly, failure to thrive, hypoglycemia, hyperlactatemia, hyperuricemia and hyperlipidemia. Type IIIa involves both the liver and muscle, and IIIb solely the liver. The liver symptoms generally improve with age. Type IV usually presents in the first year of life, with hepatomegaly and growth retardation. The disease in general is progressive to cirrhosis. Type VI and IX are a heterogeneous group of diseases caused by a deficiency of the liver phosphorylase and phosphorylase kinase system. There is no hyperuricemia or hyperlactatemia. Type XI is characterized by hepatic glycogenosis and renal Fanconi syndrome. Type II is a prototype of inborn lysosomal storage diseases and involves many organs but primarily the muscle. Types V and VII involve only the muscle.

Guidelines for management of glycogen storage disease type I - European Study on Glycogen Storage Disease Type I (ESGSD I)

Life-expectancy in glycogen storage disease type I (GSD I) has improved considerably. Its relative rarity implies that no metabolic centre has experience of large series of patients and experience with long-term management and follow-up at each centre is limited. There is wide variation in methods of dietary and pharmacological treatment. Based on the data of the European Study on Glycogen Storage Disease Type I, discussions within this study group, discussions with the participants of the international SHS-symposium 'Glycogen Storage Disease Type I and II: Recent Developments, Management and Outcome' (Fulda, Germany; 22-25th November 2000) and on data from the literature, guidelines are presented concerning: (1). diagnosis, prenatal diagnosis and carrier detection; (2). (biomedical) targets; (3). recommendations for dietary treatment; (4). recommendations for pharmacological treatment; (5). metabolic derangement/intercurrent infections/emergency treatment/preparation elective surgery; and (6). management of complications (directly) related to metabolic disturbances and complications which may develop with ageing and their follow-up.

CONCLUSION

In this paper guidelines for the management of GSD I are presented.

Intestinal function in glycogen storage disease type I

Glycogen storage disease type I (GSD I) (McKusick 232200) is caused by inherited defects of the glucose-6-phosphatase complex. Patients with GSD Ia as well as patients with GSD lb may suffer from intermittent diarrhoea, which seems to worsen with age. The cause of this diarrhoea is unknown. This study describes the results of investigations of intestinal functions and morphology in patients with GSD Ia and GSD lb, which were performed to detect a common cause for chronic diarrhoea in GSD I. The following were investigated: faecal fat excretion, faecal alpha1-antitrypsin and faecal chymotrypsin, expiratory H2 concentrations, persorption of cornstarch in urine and colonic biopsies. With the investigations presented in this study, no common cause for diarrhoea in GSD I was found. In GSD lb loss of mucosal barrier function due to inflammation, documented by increased faecal alpha1-antitrypsin excretion (3.5-9.6 mg/g dry faeces) and inflammation in the colonic biopsies, seems to be the main cause. The inflammation is most likely related to disturbed neutrophil function, which is often found in GSD lb. Whether another cause is involved in GSD Ia and in GSD Ib, related to the disturbed function of glucose-6-phosphatase in the enterocyte, remains to be investigated.

Glucose-6-phosphatase mutation G188R confers an atypical glycogen storage disease type 1b phenotype

Glycogen storage disease type 1a (GSD 1a) is caused by a deficiency in microsomal glucose-6-phosphatase (G6Pase). A variant (GSD 1b) is caused by a defect in the transport of glucose-6-phosphate (G6P) into the microsome and is associated with chronic neutropenia and neutrophil dysfunction. Mutually exclusive mutations in the G6Pase gene and the G6P transport gene establish GSD la and GSD 1b as independent molecular processes and are consistent with a multicomponent translocase catalytic model. A modified translocase/catalytic unit model based on biochemical data in a G6Pase knockout mouse has also been proposed for G6Pase catalysis. This model suggests coupling of G6Pase activity and G6P transport. A 5-mo-old girl with hypoglycemia, hepatomegaly, and lactic acidemia was diagnosed with GSD 1a. She also developed neutropenia, neutrophil dysfunction, and recurrent infections characteristic of GSD 1b. Homozygous G188R mutations of the G6Pase gene were identified, but no mutations in the G6P translocase gene were found. We have subsequently identified a sibling and two unrelated patients with similar genotypic/phenotypic characteristics. The unusual association of neutrophil abnormalities in patients with homozygous G188R mutations in the G6Pase gene supports a modified translocase/catalytic unit model.

Glycogen storage disease type Ib without neutropenia

We report 2 patients with atypical glycogen storage disease type Ib without neutropenia or infectious complications. Neither patient was deficient in hepatic glucose-6-phosphatase activities in microsome-disrupted homogenates; both had mutations in the glucose-6-phosphate transporter gene, suggesting an allelic variant of glycogen storage disease type Ib.

Neutropenia, neutrophil dysfunction, and inflammatory bowel disease in glycogen storage disease type Ib: results of the European Study on Glycogen Storage Disease type I

OBJECTIVE

To investigate the incidence, the severity, and the course of neutropenia, neutrophil dysfunction, and inflammatory bowel disease (IBD) in glycogen storage disease (GSD) type Ib.

METHOD

As part of a collaborative European Study on GSD type I, a retrospective registry was established in 12 European countries that included all patients with GSD-I who were known at the centers and were born from 1960 to 1995. Of a total of 288 patients with GSD-I, 57 who had GSD-Ib form the basis of this study.

RESULTS

Neutropenia (defined as an absolute neutrophil count <1 x 10(9)/L) was found in 54 patients. In 64% of the patients neutropenia was documented before the age of 1 year, but in 18% of the patients neutropenia was first noted between the ages of 6 and 9 years. Neutropenia was persistent in 5 patients and intermittent without any clear cyclical course in 45. Neutrophil function was investigated in 18 patients with neutropenia and was abnormal in all. Perioral infections were reported in 37 patients, perianal infections in 27 patients, and protracted diarrhea in 23 patients. Findings on colonoscopy and radiologic studies in 10 of 20 patients suspected to have IBD were abnormal in all. All patients with IBD, perioral infections, and perianal infections had neutropenia.

CONCLUSIONS

Intermittent severe neutropenia is frequently found in patients with GSD-Ib. The study also indicates that IBD in GSD-Ib is underdiagnosed; up to 77% of the patients studied had evidence of IBD, all of whom had neutropenia. IBD was not detected in those with normal neutrophil counts. These findings support the notion that neutropenia and/or neutrophil dysfunction in GSD-Ib and IBD are causally related.

Glycogen storage disease type Ib: structural and mutational analysis of the microsomal glucose-6-phosphate transporter gene

Glycogen storage disease type Ib is caused by a mutation in the gene encoding microsomal glucose-6-phosphate (G6P) transporter. We determined the exon/intron organization of the G6P transporter gene. Four overlapping genomic fragments containing the entire coding region of the gene were amplified by polymerase chain reaction (PCR) using exonic primers, and their nucleotide sequences were determined. The gene spans 4.5 kb and has eight exons. All exon/intron boundaries adhered to the canonical AG/GT rule. We then designed eight pairs of PCR primers to amplify all coding exons for a mutational analysis and studied five Japanese patients with the disease. Two novel homozygous mutations were identified in two families: a three-base deletion (delV235) in exon 2 in a consanguineous family and a splicing mutation (IVS7+1G-->T) in intron 7 in a nonconsanguineous family. Patient 3 was a compound heterozygote of W118R and IVS1+1G-->A, both of which we previously identified [Kure et al., 1998: Biochem Biophys Res Commun 248:426-431]. Patients 4 and 5 were homozygotes of W118R. Including our previous study, we found a total of ten W118R alleles in nine Japanese patients. The results support our previous suggestion that W118R is prevalent among Japanese patients. The genomic sequence data and mutation spectrum obtained from the Japanese patients will facilitate genetic diagnosis of glycogen storage disease type Ib.

Glycogen storage disease type 1a in Israel: biochemical, clinical, and mutational studies

Glycogen storage disease type 1a (von Gierke disease, GSD 1a) is caused by the deficiency of microsomal glucose-6-phosphatase (G6Pase) activity which catalyzes the final common step of glycogenolysis and gluconeogenesis. The recent cloning of the G6Pase cDNA and characterization of the human G6Pase gene enabled the characterization of the mutations causing GSD 1a. This, in turn, allows the introduction of a noninvasive DNA-based diagnosis that provides reliable carrier testing and prenatal diagnosis. In this study, we report the biochemical and clinical characteristics as well as mutational analyses of 12 Israeli GSD 1a patients of different families, who represent most GSD 1a patients in Israel. The mutations, G6Pase activity, and glycogen content of 7 of these patients were reported previously. The biochemical data and clinical findings of all patients were similar and compatible with those described in other reports. All 9 Jewish patients, as well as one Muslim Arab patient, presented the R83C mutation. Two Muslim Arab patients had the V166G mutation which was not found in other patients' populations. The V166G mutation, which was introduced into the G6Pase cDNA by site-directed mutagenesis following transient expression in COS-1 cells, was shown to cause complete inactivation of the G6Pase. The characterization of all GSD 1a mutations in the Israeli population lends itself to carrier testing in these families as well as to prenatal diagnosis, which was carried out in 2 families. Since all Ashkenzai Jewish patients harbor the same mutation, our study suggests that DNA-based diagnosis may be used as an initial diagnostic step in Ashkenazi Jews suspected of having GSD 1a, thereby avoiding liver biopsy.

Oral manifestations in glycogen storage disease type 1b

Glycogen storage disease type 1b is a rare metabolic disorder which affects the transport system of glucose-6-phosphatase metabolism. As a result, hepatomegaly, failure to thrive, renal dysfunction and recurrent infections occur in affected patients. In this paper, the oral complications in three children with glycogen storage disease type 1b are discussed. Oral ulcers were a common finding, probably due to severe neutropenia and impaired neutrophil migration which characterises the onset of this rare disorder.

Characterization of the mutations in the glucose-6-phosphatase gene in Israeli patients with glycogen storage disease type 1a: R83C in six Jews and a novel V166G mutation in a Muslim Arab

Glycogen storage disease type 1a (GSD 1a), an autosomal recessive disease, is caused by the inactivity of glucose-6-phosphatase, the gene of which has been recently cloned. We report on the missense mutation C-->T at nucleotide 326 of the G6Pase gene, causing the change of the Arg codon at position 83 into a Cys codon, as the single mutation detected in six Jewish patients. This finding suggests that this mutation might be prevalent among the Jewish population. A new missense mutation T-->G at nucleotide 576 resulting in V166G was found in an Arab Muslim patient. These families may benefit now from pre- and postnatal diagnosis by analysis of DNA from blood and amniotic fluid or chorionic villus cells rather than liver biopsy. No mutations in the G6Pase gene were detected in two GSD 1b patients.

Postnatal regression of glucose transport in a patient with glycogen storage disease type 1b

Decreased 2-deoxyglucose (2-DOG) uptake is well described in the neutrophils of patients with glycogen storage disease type 1b (GSD 1b). We report a patient with GSD 1b who presented with a normal antenatal and perinatal 2-deoxyglucose uptake that showed a slow regression during the first months of life. These indicate limitations of 2-deoxyglucose uptake in the diagnosis of GSD 1b. While it appears that low uptake rate below 0.25 nmol/min in 10(6) cells is of significance, normal uptake does not rule out the presence of the disease. It seems that antenatal diagnosis of GSD 1b cannot be made by measurement of 2-deoxyglucose uptake in the fetal neutrophils.

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)

Hypoglycemia in infants

Because the infant's brain is to a large extent dependent on glucose utilization, hypoglycemia of infants can have grave effects on brain function, and it is important to diagnose it and, when possible, treat it promptly. Causes of hypoglycemia in infants are (a) excess insulin secretion, (b) factitious hyperinsulinemia, (c) GH or ACTH deficiency, (d) primary glucocorticoid deficiency, (e) defects of the enzymes involved in hepatic glucose production, or (f) defects in hepatic fatty acid oxidation.

Impaired carbohydrate metabolism of polymorphonuclear leukocytes in glycogen storage disease Ib

This study measures hexose monophosphate (HMP) shunt activity, glycolytic rate, and glucose transport in PMN and lymphocytes of patients with glycogen storage disease (GSD) type Ib as compared with controls and with GSD Ia patients. HMP shunt activity and glycolysis were significantly lower in intact PMN cells of GSD Ib patients as compared with GSD Ia patients and with controls. These activities were above normal levels in disrupted GSD Ib PMN. HMP shunt activity and glycolytic rates in lymphocytes were similar in all three groups studied. The rate of 2-deoxyglucose transport into GSD Ib PMN was 30% of that into cells of normal controls. In GSD Ib lymphocytes or in GSD Ia PMN and lymphocytes transport was normal. The striking limitation of glucose transport across the cell membrane of the PMN of GSD Ib patients may account for the impairment of leukocyte function that is characteristic of GSD Ib, but not found in GSD Ia patients.

A new microtechnique for the analysis of the human hepatic microsomal glucose-6-phosphatase system

A microtechnique has been developed which enables a complete kinetic analysis of the human hepatic microsomal glucose-6-phosphatase system to be carried out in microsomes isolated from very small liver samples. Complete or partial deficiencies of any of the proteins of the glucose-6-phosphatase system resulting in Type 1a, 1b, 1c or 1d glycogen storage disease can be therefore be diagnosed using hepatic needle biopsy samples, whereas previous methods of diagnosis needed large wedge biopsy samples requiring laparotomy.

Diagnosis of type 1a and type 1c glycogen storage diseases in adults

The hepatic glucose-6-phosphatase system was studied with a novel microanalytical technique in adult patients undergoing liver biopsy. 4 patients were diagnosed as having type 1 glycogen storage disease (GSD). 3 of these patients, who had hypoglycaemic symptoms, had variations of type 1a GSD, which is caused by a defect in the hepatic microsomal glucose-6-phosphatase enzyme. The fourth, with hepatomegaly and no hypoglycaemic symptoms, had a normal glucose-6-phosphatase enzyme but a defect in the hepatic microsomal phosphate/pyrophosphate translocase T2; this is the first report of an adult with type 1c GSD. Adult type 1 GSD should be considered in patients with unresolved hypoglycaemic symptoms and/or unresolved hepatomegaly.

Impaired glucose transport in polymorphonuclear leukocytes in glycogen storage disease Ib

A study of 2-deoxyglucose transport into polymorphonuclear leukocytes (PMN) was performed in three patients with glycogen storage disease (GSD) type Ib. The rate of 2-deoxyglucose transport into GSD Ib PMN was 30% of that of cells of normal controls. In GSD Ib lymphocytes, transport was normal. Km for 2-deoxyglucose in the PMN of one patient was within the normal range. The reduced transport was not due to the elevation in Km for 2-deoxyglucose nor to the decreased rate of phosphorylation of 2-deoxyglucose. The striking limitation of glucose transport across the cell membrane may account for the impairment of leukocyte function which is characteristic of GSD Ib.

Glycogen storage disease type IB: a new model of genetic disorders involving the transport system of intracellular membrane

Our studies have revealed that the primary lesion of GSD type Ib exists in the G6P transport system in the microsomal membrane. Distinct evidence for the existence of a specific G6P transport system in microsomal membrane was obtained through these studies. This is the first example of a genetic disorder involving the transport system of an intracellular membrane. HHH syndrome (hyperornithinemia, hyperammonemia, and homocitrullinuria), in which the transport of ornithine to the mitochondria is presumed to be defective, may be another example belonging to this category of genetic disorders (18-20). A possibility exists that there are many other disorders due to defects in the membrane transport of intracellular organelles.

Biochemical diagnosis of type 1b glycogen storage disease

A child with the classical signs and symptoms of Type 1 glycogen storage disease is presented, who on investigation was shown to have a recently described variant of this disease known as Type 1b glycogen storage disease. A reliable and simple procedure for the diagnosis and differentiation of Types 1 and 1b glycogen storage disease is described, as the conventional diagnostic approach of assaying glucose-6-phosphate phosphohydrolase in frozen tissue will not diagnose Type 1b glycogen storage disease. A portion of biopsy tissue should be maintained at a temperature near 0 degrees C (but not frozen) and the remainder frozen. Glucose-6-phosphate phosphohydrolase assays are carried out on the tissue homogenates of both portions. In Type 1 glycogen storage disease, glucose-6-phosphate phosphohydrolase activity will be low or absent in both frozen and unfrozen tissues. In Type 1b glycogen storage disease the frozen tissue homogenate will exhibit normal glucose-6-phosphate phosphohydrolase activity due to the disruption of the microsomes by ice crystals, while in the unfrozen tissue low levels of glucose-6-phosphate phosphohydrolase activity will be detected.

A direct evidence for defect in glucose-6-phosphate transport system in hepatic microsomal membrane of glycogen storage disease type IB

Uptake of glucose-6-phosphate by microsomes of hepatocyte in rats, human controls and patients with glycogen storage disease type Ia and Ib was studied. In rat the uptake of glucose-6-phosphate increased rapidly and reached to a plateau, but mannose-6-phosphate was not accumulated. These findings indicate that a glucose-6-phosphate specific transport system exists in the microsomal membrane. In human controls and patients with glycogen storage disease type Ia the uptake of glucose-6-phosphate was clearly observed. On the other hand, no accumulation of it was detected in a patient with glycogen storage disease type Ib. These data provide a direct evidence of the defect in the glucose-6-phosphate transport system of hepatic microsomal membrane in glycogen storage disease type Ib.