Complete genomic structure and mutational spectrum of PHKA2 in patients with x-linked liver glycogenosis type I and II.
X-linked liver glycogenosis (XLG) is probably the most frequent glycogen-storage disease. XLG can be divided into two subtypes: XLG I, with a deficiency in phosphorylase kinase (PHK) activity in peripheral blood cells and liver; and XLG II, with normal in vitro PHK activity in peripheral blood cells and with variable activity in liver. Both types of XLG are caused by mutations in the same gene, PHKA2, that encodes the regulatory alpha subunit of PHK. To facilitate mutation analysis in PHKA2, we determined its genomic structure. The gene consists of 33 exons, spanning >/=65 kb. By SSCP analysis of the different PHKA2 exons, we identified five new XLG I mutations, one new XLG II mutation, and one mutation present in both a patient with XLG I and a patient with XLG II, bringing the total to 19 XLG I and 12 XLG II mutations. Most XLG I mutations probably lead to truncation or disruption of the PHKA2 protein. In contrast, all XLG II mutations are missense mutations or small in-frame deletions and insertions. These results suggest that the biochemical differences between XLG I and XLG II might be due to the different nature of the disease-causing mutations in PHKA2. XLG I mutations may lead to absence of the alpha subunit, which causes an unstable PHK holoenzyme and deficient enzyme activity, whereas XLG II mutations may lead to in vivo deregulation of PHK, which might be difficult to demonstrate in vitro. (+info)
Systemic correction of the muscle disorder glycogen storage disease type II after hepatic targeting of a modified adenovirus vector encoding human acid-alpha-glucosidase.
This report demonstrates that a single intravenous administration of a gene therapy vector can potentially result in the correction of all affected muscles in a mouse model of a human genetic muscle disease. These results were achieved by capitalizing both on the positive attributes of modified adenovirus-based vectoring systems and receptor-mediated lysosomal targeting of enzymes. The muscle disease treated, glycogen storage disease type II, is a lysosomal storage disorder that manifests as a progressive myopathy, secondary to massive glycogen accumulations in the skeletal and/or cardiac muscles of affected individuals. We demonstrated that a single intravenous administration of a modified Ad vector encoding human acid alpha-glucosidase (GAA) resulted in efficient hepatic transduction and secretion of high levels of the precursor GAA proenzyme into the plasma of treated animals. Subsequently, systemic distribution and uptake of the proenzyme into the skeletal and cardiac muscles of the GAA-knockout mouse was confirmed. As a result, systemic decreases (and correction) of the glycogen accumulations in a variety of muscle tissues was demonstrated. This model can potentially be expanded to include the treatment of other lysosomal enzyme disorders. Lessons learned from systemic genetic therapy of muscle disorders also should have implications for other muscle diseases, such as the muscular dystrophies. (+info)
Frequency of glycogen storage disease type II in The Netherlands: implications for diagnosis and genetic counselling.
Glycogen storage disease type II (GSD H) is an autosomal recessive myopathy. Early and late-onset phenotypes are distinguished - infantile, juvenile and adult. Three mutations in the acid alpha-glucosidase gene are common in the Dutch patient population: IVS1(-13T-->G), 525delT and delexon18. 63% of Dutch GSD II patients carry one or two of these mutations, and the genotype-phenotype correlation is known. To determine the frequency of GSD II, we have screened an unselected sample of neonates for the occurrence of these three mutations. Based on the calculated carrier frequencies, the predicted frequency of the disease is 1 in 40000 divided by 1 in 138 000 for infantile GSD II and 1 in 57 000 for adult GSD II. This is about two to four times higher than previously suggested, which is a reason to become more familiar with the presentation of GSD II in its different clinical forms and to adjust the risk assessment for genetic counselling. (+info)
Human acid alpha-glucosidase from rabbit milk has therapeutic effect in mice with glycogen storage disease type II.
Pompe's disease or glycogen storage disease type II (GSDII) belongs to the family of inherited lysosomal storage diseases. The underlying deficiency of acid alpha-glucosidase leads in different degrees of severity to glycogen storage in heart, skeletal and smooth muscle. There is currently no treatment for this fatal disease, but the applicability of enzyme replacement therapy is under investigation. For this purpose, recombinant human acid alpha-glucosidase has been produced on an industrial scale in the milk of transgenic rabbits. In this paper we demonstrate the therapeutic effect of this enzyme in our knockout mouse model of GSDII. Full correction of acid alpha-glucosidase deficiency was obtained in all tissues except brain after a single dose of i.v. enzyme administration. Weekly enzyme infusions over a period of 6 months resulted in degradation of lysosomal glycogen in heart, skeletal and smooth muscle. The tissue morphology improved substantially despite the advanced state of disease at the start of treatment. The results have led to the start of a Phase II clinical trial of enzyme replacement therapy in patients. (+info)
Amniotic cell 4-methylumbelliferyl-alpha-glucosidase activity for prenatal diagnosis of Pompe's disease.
Using a simple fluorometric assay for alpha-glucosidase activity of cultured amniotic cells, we have monitored two pregnancies from families at risk for Pompe's disease. The fetus was judged to be affected in one, the pregnancy being terminated and unaffected in the other. The accuracy of these predictions was confirmed. These results suggest that this assay allows accurate prenatal diagnosis of Pompe's disease, three weeks after diagnostic amniocentesis. (+info)
Pompe's disease or type IIa glycogenosis.
This is the report of a five-month-old child presenting clinical evidence of Pompe's disease: severe hypotonicity, hyporeflexia and congestive heart failure. The ECG showed a short PR interval, the chest radiography disclosed marked cardiomegaly, and the echocardiogram revealed marked left ventricular hypertrophy - the most typical finding of this disease. A skeletal muscle biopsy led to final diagnosis, because in the histopathologic study marked increased glycogen accumulation was evident. Death occurred two months after symptom onset. (+info)
Evidence for a founder effect in Sicilian patients with glycogen storage disease type II.
Glycogen storage disease type II (GSD II) is an autosomal recessive inherited disorder due to the deficiency of the enzyme acid alpha-glucosidase, which causes an accumulation of glycogen in lysosomes. The deletion of exon 18 (delta 18) is a frequent mutation associated with a severe phenotype. We analyzed 25 Italian patients, 5 of whom were found to be delta 18 carriers. All these 5 patients came from Catania, a town in Sicily. We report on the analysis of 5 intragenic single-point polymorphic markers in the delta 18 patients and on the subsequent characterization of a delta 18-associated haplotype. The frequency of this haplotype in GSD II patients and normal individuals was 1 and 0.196, respectively (chi(2) = 20.9; p < 0.001). The high frequency of the delta 18 allele in this Italian subpopulation is likely to be due to a founder effect. (+info)
Determination of acid alpha-glucosidase protein: evaluation as a screening marker for Pompe disease and other lysosomal storage disorders.
BACKGROUND: In recent years, there have been significant advances in the development of enzyme replacement and other therapies for lysosomal storage disorders (LSDs). Early diagnosis, before the onset of irreversible pathology, has been demonstrated to be critical for maximum efficacy of current and proposed therapies. In the absence of a family history, the presymptomatic detection of these disorders ideally can be achieved through a newborn screening program. One approach to the development of such a program is the identification of suitable screening markers. In this study, the acid alpha-glucosidase protein was evaluated as a marker protein for Pompe disease and potentially for other LSDs. METHODS: Two sensitive immunoquantification assays for the measurement of total (precursor and mature) and mature forms of acid alpha-glucosidase protein were used to determine the concentrations in plasma and dried blood spots from control and LSD-affected individuals. RESULTS: In the majority of LSDs, no significant increases above control values were observed. However, individuals with Pompe disease showed a marked decrease in acid alpha-glucosidase protein in both plasma and whole blood compared with unaffected controls. For plasma samples, this assay gave a sensitivity of 95% with a specificity of 100%. For blood spot samples, the sensitivity was 82% with a specificity of 100%. CONCLUSIONS: This study demonstrates that it is possible to screen for Pompe disease by screening the concentration of total acid alpha-glucosidase in plasma or dried blood spots. (+info)