Diagnosis of Pompe's disease using leukocyte preparations. Kinetic and immunological studies of 1,4-alpha-glucosidase in human fetal and adult tissues and cultured cells

Lysosomal storage disorders affecting the heart: a review

Lysosomal storage disorders (LSD) comprise a group of diseases caused by a deficiency of lysosomal enzymes, membrane transporters or other proteins involved in lysosomal biology. Lysosomal storage disorders result from an accumulation of specific substrates, due to the inability to break them down. The diseases are classified according to the type of material that is accumulated; for example, lipid storage disorders, mucopolysaccharidoses and glycoproteinoses. Cardiac disease is particularly important in lysosomal glycogen storage diseases (Pompe and Danon disease), mucopolysaccharidoses and in glycosphingolipidoses (Anderson-Fabry disease). Various disease manifestations may be observed including hypertrophic and dilated cardiomyopathy, coronary artery disease and valvular diseases. Endomyocardial biopsies can play an important role in the diagnosis of these diseases. Microscopic features along with ancillary tests like special stains and ultrastructural studies help in the diagnosis of these disorders. Diagnosis is further confirmed based upon enzymatic and molecular genetic analysis. Emerging evidence suggests that Enzyme replacement therapy (ERT) substantially improves many of the features of the disease, including some aspects of cardiac involvement. The identification of these disorders is important due to the availability of ERT, the need for family screening, as well as appropriate patient management and counseling.

Pompe disease: early diagnosis and early treatment make a difference

Pompe disease (glycogen storage disease type II or acid maltase deficiency) is a lysosomal disorder in which acid α-glucosidase (GAA) deficiencies lead to intralysosomal accumulation of glycogen in all tissues; most notably in skeletal muscles. Both the patient's age at the onset of Pompe disease symptoms and the rate of deterioration caused by the disease can vary considerably. In classical infant-onset Pompe disease (IOPD), symptoms start very early in life, and death occurs soon afterward if the disease remains untreated. In later-onset Pompe disease, symptoms are slower to appear, and patients often progress to wheelchair confinement and eventual respiratory failure. A diagnosis can be made by screening for GAA in dried blood samples, followed either by GAA assessment in lymphocytes or in fibroblasts or by the genetic analysis of mutations. Treatment by enzyme replacement therapy (ERT) with alglucosidase alfa was approved for human use in 2006. In classical IOPD, treatment significantly lengthens survival and improves motor development and cardiac function. The sooner ERT begins, the better are the results. Newborn screening aims to take advantage of different technologies for diagnosing and treating newborns early on and it yields better outcomes. However, newborns diagnosed early and other long-term survivors may encounter fresh problems, making up a new phenotype of IOPD patients. Further modifications of the treatment, such as a decrease in immune responses to ERT, a higher dosage, a better uptake formulation, and gene therapy delivered locally or systemically are being explored.

The use of dried blood spot samples in the diagnosis of lysosomal storage disorders--current status and perspectives

Dried blood spot (DBS) methods are currently available for identification of a range of lysosomal storage disorders (LSDs). These disorders are generally characterized by a deficiency of activity of a lysosomal enzyme and by a broad spectrum of phenotypes. Diagnosis of LSD patients is often delayed, which is of particular concern as therapeutic outcomes (e.g. enzyme replacement therapy) are generally more favorable in early disease stages. Experts in the field of LSDs diagnostics and screening programs convened and reviewed experiences with the use of DBS methods, and discuss the diagnostic challenges, possible applications and quality programs in this paper. Given the easy sampling and shipping and stability of samples, DBS has evident advantages over other laboratory methods and can be particularly helpful in the early identification of affected LSD patients through neonatal screening, high-risk population screening or family screening.

Cardiac arrhythmias following anesthesia induction in infantile-onset Pompe disease: a case series

BACKGROUND

Patients with infantile-onset Pompe disease suffer from marked hypertrophic cardiomyopathy and an increased risk of arrhythmia. A noncompliant left ventricle predisposes these infants to diastolic heart failure with elevated left ventricular enddiastolic pressure (LVEDP); these patients also commonly develop systolic heart failure. Given this baseline cardiac physiology, coronary perfusion pressure becomes highly sensitive to abrupt changes in diastolic blood pressure (DBP).

METHODS

We retrospectively reviewed the experiences of 139 patients enrolled in clinical trials investigating the treatment of infantile-onset Pompe disease with recombinant human acid alpha-glucosidase (rhGAA). Adverse events were screened for those involving anesthesia.

RESULTS

Nine patients (6%) with infantile-onset Pompe disease experienced an arrhythmia or cardiopulmonary arrest soon after the induction of general anesthesia. Of these events, propofol was involved in four arrhythmias; sevoflurane without propofol was associated with an additional two. Deaths resulting from arrhythmia appeared to correlate with left ventricular mass indices >350 g x m(-2).

CONCLUSIONS

With the advent of enzyme replacement therapy (ERT) using rhGAA, and increased survivability, more infantile Pompe patients will likely present for surgical procedures. Additional care in maximizing coronary perfusion pressure and minimizing arrhythmia risk must be given. For these reasons, it is recommended that anesthesia for infantile Pompe patients specifically avoid propofol or high concentrations of sevoflurane and, instead, use an agent such as ketamine as the cornerstone for induction in order to better support coronary perfusion pressure and to avoid decreasing DBP with vasodilatory agents.

Acid alpha-glucosidase deficiency (Pompe disease)

The development and recent approval of recombinant acid alpha-glucosidase for enzyme replacement therapy have been major milestones in Pompe disease research. Acid alpha-glucosidase is the enzyme responsible for degradation of glycogen polymers to glucose in the acidic milieu of the lysosomes. Cardiac and skeletal muscles are the two major tissues affected by the accumulation of glycogen within the lysosomes. Both cardiomyopathy and skeletal muscle myopathy are observed in patients with complete enzyme deficiency; this form of the disease is fatal within the first year of life. Skeletal muscle myopathy eventually leading to respiratory insufficiency is the predominant manifestation of partial enzyme deficiency. The recombinant enzyme alglucosidase alfa is the first drug ever approved for this devastating disorder. This review discusses the benefits and the shortcomings of the new therapy.

Glycogen storage disease: clinical, biochemical, and molecular heterogeneity

Glycogen storage diseases (GSDs) are characterized by abnormal inherited glycogen metabolism in the liver, muscle, and brain and divided into types 0 to X. GSD type I, glucose 6-phosphatase system, has types Ia, Ib, Ic, and Id, glucose 6-phosphatase, glucose 6-phosphate translocase, pyrophosphate translocase, and glucose translocase deficiencies, respectively. GSD type II is caused by defective lysosomal alpha-glucosidase (GAA), subdivided into 4 onset forms. GSD type III, amylo-1,6-glucosidase deficiency, is subdivided into 6 forms. GSD type IV, Andersen disease or amylopectinosis, is caused by deficiency of the glycogen-branching enzyme in numerous forms. GSD type V, McArdle disease or muscle phosphorylase deficiency, is divided into 2 forms. GSD type VI is characterized by liver phosphorylase deficiency. GSD type VII, phosphofructokinase deficiency, has 2 subtypes. GSD types VIa, VIII, IX, or X are supposedly caused by tissue-specific phosphorylase kinase deficiency. GSD type 0, glycogen synthase deficiency, is divided into 2 subtypes.

A new diagnostic assay for glycogen storage disease type II in mixed leukocytes

We have established a new method for the enzymatic diagnosis of glycogen storage disease type II (Pompe disease or acid maltase deficiency) using mixed leukocytes. The method employs glycogen and 4-methylumbelliferyl-alpha-D-glucopyranoside (4MU-alphaGlc) as substrates for measuring the lysosomal acid alpha-glucosidase (acid alphaGlu) activity, and incorporates acarbose to eliminate the interference of unrelated alpha-glucosidases (predominantly maltase-glucoamylase). It is shown that 3.0 micromol/L acarbose completely inhibits the maltase-glucoamylase activity at pH 4.0, but the lysosomal acid alphaGlu activity by less than 5%. With this method, we determined the acid alphaGlu activity in mixed leukocytes from 25 patients with glycogen storage disease type II (2 infantile and 23 late-onset cases), one GAA2/GAA2 homozygote and 30 healthy subjects. In the assay with glycogen as substrate, the addition of acarbose created a clear separation between the patient and the control ranges. In the assay with 4MU-alphaGlc as substrate, the two ranges were fully separated but remained very close despite the use of acarbose. The separation of the patient and normal ranges was improved considerably by taking the ratio of acarbose-inhibited over uninhibited activity. A GAA2/GAA2 homozygote was correctly diagnosed with 4MU-alphaGlc but misdiagnosed as patient when glycogen was used as substrate. We conclude that the inclusion of 3.0 micromol/L acarbose in the assays with glycogen and 4MU-alphaGlc substrates at pH 4.0 allows for the specific measurement of lysosomal acid alphaGlu activity in mixed leukocytes, thus enabling a reliable diagnosis of glycogen storage disease type II in this specimen.

Comparison of maltose and acarbose as inhibitors of maltase-glucoamylase activity in assaying acid α-glucosidase activity in dried blood spots for the diagnosis of infantile Pompe disease

PURPOSE

The study's purpose was to compare acarbose and maltose as inhibitors of maltase-glucoamylase activity for determining acid alpha-glucosidase activity in dried blood spot specimens for early identification of patients with infantile Pompe disease, a severe form of acid alpha-glucosidase deficiency.

METHODS

Acid alpha-glucosidase activities in dried blood spot extracts were determined fluorometrically using the artificial substrate 4-methylumbelliferyl-alpha-D-pyranoside. Acarbose or maltose was used to inhibit maltase-glucoamylase, an enzyme present in polymorphonuclear neutrophils that contributes to the total alpha-glucosidase activity at acidic pH.

RESULTS

Complete discrimination between patients with proven infantile Pompe disease (n = 20), obligate heterozygotes (n = 16), and controls (n = 150) was achieved using 8 micromol/L acarbose as the inhibitor. Higher acarbose concentration (80 micromol/L) did not improve the assay. By using 4 mM maltose as the inhibitor, heterozygotes and patients were not completely separated. The results using acarbose compared well with those using the skin fibroblast assay in the same group of patients with proven infantile Pompe disease.

CONCLUSION

Acid alpha-glucosidase activity measurements in dried blood spot extracts can reliably detect infantile Pompe disease in patients. The convenience of collecting and shipping dried blood specimens plus rapid turnaround time makes this assay an attractive alternative to established methods.

Direct multiplex assay of enzymes in dried blood spots by tandem mass spectrometry for the newborn screening of lysosomal storage disorders

Tandem mass spectrometry is currently used in newborn screening programmes to quantify the level of amino acids and acylcarnitines in dried blood spots for detection of metabolites associated with treatable diseases. We have developed assays for lysosomal enzymes in rehydrated dried blood spots in which a set of substrates is added and the set of corresponding enzymatic products are quantified using tandem mass spectrometry with the aid of mass-differentiated internal standards. We have developed a multiplex assay of the set of enzymes that, when deficient, cause the lysosomal storage disorders Fabry, Gaucher, Hurler, Krabbe, Niemann-Pick A/B and Pompe diseases. These diseases were selected because treatments are now available or expected to emerge shortly. The discovery that acarbose is a selective inhibitor of maltase glucoamylase allows the Pompe disease enzyme, acid alpha-glucosidase, to be selectively assayed in white blood cells and dried blood spots. When tested with dried blood spots from 40 unaffected individuals and 10-12 individuals with the lysosomal storage disorder, the tandem mass spectrometry assay led to the correct identification of the affected individuals with 100% sensitivity. Many of the reagents needed for the new assays are commercially available, and those that are not are being prepared under Good Manufacturing Procedures for approval by the FDA. Our newborn screening assay for Krabbe disease is currently being put in place at the Wadsworth Center in New York State for the analysis of approximately 1000 dried blood spots per day. Summary We have developed tandem mass spectrometry for the direct assay of lysosomal enzymes in rehydrated dried blood spots that can be implemented for newborn screening of lysosomal storage disorders. Several enzymes can be analysed by a single method (multiplex analysis) and in a high-throughput manner appropriate for newborn screening laboratories.

Glycogen storage disease type II: enzymatic screening in dried blood spots on filter paper

BACKGROUND

Glycogen storage disease II is characterized by a deficiency of the lysosomal enzyme acid alpha-glucosidase. Currently, glycogen storage disease II is diagnosed by demonstrating the virtual absence or a marked reduction of acid alpha-glucosidase activity in muscle biopsies, cultured fibroblasts, or purified lymphocytes. Early diagnosis and treatment of glycogen storage disease II are considered to be critical for maximum efficacy of the enzyme replacement therapies that are in development. However, these existing diagnostic methods are not suited for newborn screening. We developed an assay useful for newborn screening for glycogen storage disease II.

METHODS

A series of three enzyme assays to measure the alpha-glucosidase activities in dried blood spots on filter paper was developed. The measurement of acid alpha-glucosidase activity with minimal interference by other alpha-glucosidases was accomplished using maltose as an inhibitor. The method was used on samples from glycogen storage disease II patients, obligate heterozygotes, and healthy controls.

RESULTS

Glycogen storage disease II patients were distinguished from carriers and healthy controls using the series of enzyme assays.

CONCLUSIONS

We developed a simple and noninvasive screening method for glycogen storage disease II. The method could be incorporated into newborn screening.

Direct multiplex assay of lysosomal enzymes in dried blood spots for newborn screening

BACKGROUND

Newborn screening for deficiency in the lysosomal enzymes that cause Fabry, Gaucher, Krabbe, Niemann-Pick A/B, and Pompe diseases is warranted because treatment for these syndromes is now available or anticipated in the near feature. We describe a multiplex screening method for all five lysosomal enzymes that uses newborn-screening cards containing dried blood spots as the enzyme source.

METHODS

We used a cassette of substrates and internal standards to directly quantify the enzymatic activities, and tandem mass spectrometry for enzymatic product detection. Rehydrated dried blood spots were incubated with the enzyme substrates. We used liquid-liquid extraction followed by solid-phase extraction with silica gel to remove buffer components. Acarbose served as inhibitor of an interfering acid alpha-glucosidase present in neutrophils, which allowed the lysosomal enzyme implicated in Pompe disease to be selectively analyzed.

RESULTS

We analyzed dried blood spots from 5 patients with Gaucher, 5 with Niemann-Pick A/B, 11 with Pompe, 5 with Fabry, and 12 with Krabbe disease, and in all cases the enzyme activities were below the minimum activities measured in a collection of heterozygous carriers and healthy noncarrier individuals. The enzyme activities measured in 5-9 heterozygous carriers were approximately one-half those measured with 15-32 healthy individuals, but there was partial overlap of each condition between the data sets for carriers and healthy individuals.

CONCLUSION

For all five diseases, the affected individuals were detected. The assay can be readily automated, and the anticipated reagent and supply costs are well within the budget limits of newborn-screening centers.

Determination of Acid α-Glucosidase Activity in Blood Spots as a Diagnostic Test for Pompe Disease

Background: Pompe disease is an autosomal recessive disorder of glycogen metabolism that is characterized by a deficiency of the lysosomal acid α-glucosidase. Enzyme replacement therapy for the infantile and juvenile forms of Pompe disease currently is undergoing clinical trials. Early diagnosis before the onset of irreversible pathology is thought 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. Currently, the clinical diagnosis of Pompe disease is confirmed by the virtual absence, in infantile onset, or a marked reduction, in juvenile and adult onset, of acid α-glucosidase activity in muscle biopsies and cultured fibroblasts. These assays are invasive and not suited to large-scale screening.

Methods: A sensitive immune-capture enzyme activity assay for the measurement of acid α-glucosidase protein was developed and used to determine the activity of this enzyme in dried-blood spots from newborn and adult controls, Pompe-affected individuals, and obligate heterozygotes.

Results: Pompe-affected individuals showed an almost total absence of acid α-glucosidase activity in blood spots. The assay showed a sensitivity and specificity of 100% for the identification of Pompe-affected individuals.

Conclusions: The determination of acid α-glucosidase activity in dried-blood spots is a useful, noninvasive diagnostic assay for the identification of Pompe disease. With further validation, this procedure could be adapted for use with blood spots collected in newborn-screening programs.

Diagnosis and prevention of lysosomal storage diseases in Russia

A special programme for the diagnosis and prevention of lysosomal storage diseases (LSD) was developed in the former USSR. All the patients from 814 families at risk were investigated using biochemical techniques. In total, 363 patients with mucopolysaccharidoses (MPS), mucolipidoses, glycoproteinoses, sphingolipidoses and other LSD were diagnosed; 55 families at risk sought prenatal diagnosis and 67 fetuses were investigated for MPS (types I, II, IIIA and IIIB, VI), Tay-Sachs disease, Sandhoff disease, GM1-gangliosidosis, metachromatic leukodystrophy, mannosidosis, Gaucher disease and multiple sulphatidosis; 17 affected fetuses were diagnosed and aborted. There was an ethnic distribution of different lysosomal storage diseases in the former USSR.

Diagnosis of glycogen storage disease

Glycogen storage diseases are associated with more than 15 different enzyme deficiencies and can be clinically divided mainly into two groups, those that affect primarily the liver and those that affect principally the muscle. In this report each glycogenosis has been clinically and biochemically documented and possibilities for an accurate and prompt diagnosis of the various types have been summarized. Most of the patients suffering from type II, type III, type IV and type VIa can easily be diagnosed by analysis of peripheral blood cells without the need for tissue biopsies. First trimester diagnosis using chorionic villi is feasible for severe forms of the glycogenoses, type IIa, type IIIa and type IV.

Heat-stable protein that stimulates acid alpha-glucosidase

A hot-water extract of bovine spleen and guinea pig liver exhibited the ability to enhance acid alpha-glucosidase activity, with methylumbelliferyl alpha-glucoside, glycogen or maltose as substrate. The level of activator required for maximal stabilization was similar for all three substrates, indicating direct action on the enzyme rather than on substrate. The stimulator was partially purified by chromatography with gel-permeation (apparent Mr 20,000-24,000), ion-exchange and C4 reverse-phase columns. It was retained by a narrow-pore dialysis tubing and destroyed by treatment with Pronase, and is presumably a protein. The stimulating protein protected the enzyme against denaturation by heat or incubation with a buffer of high ionic strength in the absence of substrate. RNA inhibited the enzyme, and the activator protein was able to counteract the effect. Activating material was found in a variety of mouse and rat tissues, as well as human urine.

Primary (genetic) cardiomyopathies in infancy. A survey of possible disorders and guidelines for diagnosis

This is a survey of genetic metabolic diseases in which cardiomyopathy is typical or can be the leading symptom in infancy. Apart from the well-known Pompe disease, several other storage disorders, mitochondrial disorders, and miscellaneous conditions (particularly the carnitine deficiency syndromes) may be seen in this way. Since prompt diagnosis may be mandatory for genetic counselling, and sometimes for specific treatment, guidelines for clinical, cardiological, and laboratory work-up are given.

First trimester diagnosis of Pompe's disease (glycogenosis type II) with normal outcome: assay of acid alpha-glucosidase in chorionic villous biopsy using antibodies

Prenatal diagnosis of glycogenosis type II was performed by direct assay of acid alpha-glucosidase (EC 3.2.1.20) in chorionic villous biopsy obtained by transcervical cannula aspiration from a pregnancy at risk in the 10th week of gestation. The exact value of the enzyme activity estimated by the use of antibody preparations for purified human liver acid alpha-glucosidase was in the heterozygous range, and so the homozygous enzyme deficiency could be excluded. The subsequent analysis of cells cultured from amniocentesis sampling in the 18th week of gestation resulted in a similar outcome. The study with antibodies showed that in 23 control chorionic villi obtained during gestational ages between 7-13 weeks, 1-15% of the total alpha-glucosidase activity at pH 4.0 were due to renal or neutral enzyme. This indicates that it may be important to employ antibodies for prenatal diagnosis using chorionic villous sampling. A healthy and unaffected boy was born. The biochemical values obtained from an umbilical blood specimen were in accordance with the results of the prenatal diagnosis.