Effects of a higher dose of alglucosidase alfa on ventilator-free survival and motor outcome in classic infantile Pompe disease: an open-label single-center study.

BACKGROUND: Though enzyme-replacement therapy (ERT) with alglucosidase alfa has significantly improved the prospects for patients with classic infantile Pompe disease, some 50 % of treated infants do not survive ventilator-free beyond the age of 3 years. We investigated whether higher and more frequent dosing of alglucosidase alfa improves outcome. METHODS: Eight cross-reactive immunological material (CRIM) positive patients were included in the study. All had fully deleterious mutations in both GAA alleles. Four received a dose of 20 mg/kg every other week (eow) and four received 40 mg/kg/week. Survival, ventilator-free survival, left-ventricular mass index (LVMI), motor outcome, infusion-associated reactions (IARs), and antibody formation were evaluated. RESULTS: All eight patients were alive at study end, seven of them remained ventilator-free. The patient who became ventilator dependent was treated with 20 mg/kg eow. Three of the four patients receiving 20 mg/kg eow learned to walk; two of them maintained this ability at study end. All four patients receiving 40 mg/kg/week acquired and maintained the ability to walk at study end (ages of 3.3-5.6 years), even though their baseline motor functioning was poorer. There were no apparent differences between the two dose groups with respect to the effect of ERT on LVMI, the number of IARs and antibody formation. CONCLUSIONS: Our data may suggest that a dose of 40 mg/kg/week improves outcome of CRIM positive patients over that brought by the currently recommended dose of 20 mg/kg eow. Larger studies are needed to draw definite conclusions.

Muscle fiber-type distribution, fiber-type-specific damage, and the Pompe disease phenotype.

Pompe disease is a lysosomal storage disorder caused by acid α-glucosidase deficiency and characterized by progressive muscle weakness. Enzyme replacement therapy (ERT) has ameliorated patients' perspectives, but reversal of skeletal muscle pathology remains a challenge. We studied pretreatment biopsies of 22 patients with different phenotypes to investigate to what extent fiber-type distribution and fiber-type-specific damage contribute to clinical diversity. Pompe patients have the same fiber-type distribution as healthy persons, but among nonclassic patients with the same GAA mutation (c.-32-13T>G), those with early onset of symptoms tend to have more type 2 muscle fibers than those with late-onset disease. Further, it seemed that the older, more severely affected classic infantile patients and the wheelchair-bound and ventilated nonclassic patients had a greater proportion of type 2x muscle fibers. However, as in other diseases, this may be caused by physical inactivity of those patients.

Bone, joint and tooth development in mucopolysaccharidoses: relevance to therapeutic options.

The mucopolysaccharidoses (MPS) are prominent among the lysosomal storage diseases. The intra-lysosomal accumulation of glycosaminoglycans (GAGs) in this group of diseases, which are caused by several different enzyme deficiencies, induces a cascade of responses that affect cellular functions and maintenance of the extra-cellular matrix. Against the background of normal tissue-specific processes, this review summarizes and discusses the histological and biochemical abnormalities reported in the bones, joints, teeth and extracellular matrix of MPS patients and animal models. With an eye to the possibilities and limitations of reversing the pathological changes in the various tissues, we address therapeutic challenges, and present a model in which the cascade of pathologic events is depicted in terms of primary and secondary events.

Facial-muscle weakness, speech disorders and dysphagia are common in patients with classic infantile Pompe disease treated with enzyme therapy.

Classic infantile Pompe disease is an inherited generalized glycogen storage disorder caused by deficiency of lysosomal acid α-glucosidase. If left untreated, patients die before one year of age. Although enzyme-replacement therapy (ERT) has significantly prolonged lifespan, it has also revealed new aspects of the disease. For up to 11 years, we investigated the frequency and consequences of facial-muscle weakness, speech disorders and dysphagia in long-term survivors. Sequential photographs were used to determine the timing and severity of facial-muscle weakness. Using standardized articulation tests and fibreoptic endoscopic evaluation of swallowing, we investigated speech and swallowing function in a subset of patients. This study included 11 patients with classic infantile Pompe disease. Median age at the start of ERT was 2.4 months (range 0.1-8.3 months), and median age at the end of the study was 4.3 years (range 7.7 months -12.2 years). All patients developed facial-muscle weakness before the age of 15 months. Speech was studied in four patients. Articulation was disordered, with hypernasal resonance and reduced speech intelligibility in all four. Swallowing function was studied in six patients, the most important findings being ineffective swallowing with residues of food (5/6), penetration or aspiration (3/6), and reduced pharyngeal and/or laryngeal sensibility (2/6). We conclude that facial-muscle weakness, speech disorders and dysphagia are common in long-term survivors receiving ERT for classic infantile Pompe disease. To improve speech and reduce the risk for aspiration, early treatment by a speech therapist and regular swallowing assessments are recommended.

Hemoglobin precipitation greatly improves 4-methylumbelliferone-based diagnostic assays for lysosomal storage diseases in dried blood spots.

Derivatives of 4-methylumbelliferone (4MU) are favorite substrates for the measurement of lysosomal enzyme activities in a wide variety of cell and tissue specimens. Hydrolysis of these artificial substrates at acidic pH leads to the formation of 4-methylumbelliferone, which is highly fluorescent at a pH above 10. When used for the assay of enzyme activities in dried blood spots the light emission signal can be very low due to the small sample size so that the patient and control ranges are not widely separated. We have investigated the hypothesis that quenching of the fluorescence by hemoglobin leads to appreciable loss of signal and we show that the precipitation of hemoglobin with trichloroacetic acid prior to the measurement of 4-methylumbelliferone increases the height of the output signal up to eight fold. The modified method provides a clear separation of patients' and controls' ranges for ten different lysosomal enzyme assays in dried blood spots, and approaches the conventional leukocyte assays in outcome quality.

Rate of progression and predictive factors for pulmonary outcome in children and adults with Pompe disease.

Respiratory insufficiency is a serious threat to patients with Pompe disease, a neuromuscular disorder caused by lysosomal acid alpha-glucosidase deficiency. Innovative therapeutic options which may stabilize pulmonary function have recently become available. We therefore determined proportion and severity of pulmonary involvement in patients with Pompe disease, the rate of progression of pulmonary dysfunction, and predictive factors for poor respiratory outcome. In a single-center, prospective, cohort study, we measured vital capacity (VC) in sitting and supine positions, as well as maximum inspiratory (MIP) and expiratory (MEP) mouth pressures, and end expiratory CO(2) in 17 children and 75 adults with Pompe disease (mean age 42.7 years, range 5-76 years). Seventy-four percent of all patients, including 53% of the children, had some degree of respiratory dysfunction. Thirty-eight percent had obvious diaphragmatic weakness. Males appeared to have more severe pulmonary involvement than females: at a group level, their mean VC was significantly lower than that of females (p<0.001), they used mechanical ventilation more often than females (p=0.042) and the decline over the course of the disease was significantly different between males and females (p=0.003). Apart from male gender, severe skeletal muscle weakness and long disease duration were the most important predictors of poor respiratory status. During follow-up (average 1.6 years, range 0.5-4.2 years), three patients became ventilator dependent. Annually, there were average decreases in VC in upright position of 0.9% points (p=0.09), VC in supine position of 1.2% points (p=0.049), MIP of 3.2% points (p=0.018) and MEP of 3.8% points (p<0.01). We conclude that pulmonary dysfunction in Pompe disease is much more common than generally thought. Males, patients with severe muscle weakness, and those with advanced disease duration seem most at risk.

Rate of disease progression during long-term follow-up of patients with late-onset Pompe disease.

To determine the rate of disease progression in patients with late-onset Pompe disease, we collected longitudinal data on pulmonary function and skeletal muscle strength in 16 patients whose symptoms had started in childhood or adulthood. The mean duration of follow-up was 16 years (range 4-29 years). During the follow-up period, eight patients (50%) became wheelchair bound and three (19%) became ventilator dependent. At a group level, pulmonary function deteriorated by 1.6% per year, and proximal muscle weakness progressed gradually. At the individual level, however, the rate and extent of progression varied highly between patients. In two thirds of patients, pulmonary function and muscle strength declined simultaneously and to the same extent. The remaining one third of patients showed a variable, sometimes rapidly progressive course, leading to early respirator or wheelchair dependency. These individual differences, especially in pulmonary dysfunction, indicate the need for regular monitoring every 6-12 months depending on the rate of disease progression.

Enzyme analysis for Pompe disease in leukocytes; superior results with natural substrate compared with artificial substrates.

Enzyme analysis for Pompe disease in leukocytes has been greatly improved by the introduction of acarbose, a powerful inhibitor of interfering alpha-glucosidases, which are present in granulocytes but not in lymphocytes. Here we show that the application of acarbose in the enzymatic assay employing the artificial substrate 4-methylumbelliferyl-alpha-D: -glucoside (MU-alphaGlc) is insufficient to clearly distinguish patients from healthy individuals in all cases. Also, the ratios of the activities without/with acarbose only marginally discriminated Pompe patients and healthy individuals. By contrast, when the natural substrate glycogen is used, the activity in leukocytes from patients (n = 82) with Pompe disease is at most 17% of the lowest control value. The use of artificial substrate in an assay with isolated lymphocytes instead of total leukocytes is a poor alternative as blood samples older than one day invariably yield lymphocyte preparations that are contaminated with granulocytes. To diagnose Pompe disease in leukocytes we recommend the use of glycogen as substrate in the presence of acarbose. This assay unequivocally excludes Pompe disease. To also exclude pseudo-deficiency of acid alpha-glucosidase caused by the sequence change c.271G>A (p.D91N or GAA2; homozygosity in approximately 1:1000 caucasians), a second assay employing MU-alphaGlc substrate plus acarbose or DNA analysis is required.

Molecular and functional characterization of eight novel GAA mutations in Italian infants with Pompe disease.

We characterized 29 unrelated patients presenting with the severe form of Pompe disease (Glycogen Storage Disease Type II, acid maltase deficiency) and identified 26 pathogenic mutations divided over 28 different genotypes. Among the eight new mutations, five were exonic point mutations (c.572A>G, c.1124G>T, c.1202A>G, c.1564C>G and c.1796C>A) leading to codon changes (p.Y191C, p.R375L, p.Q401R, p.P522A and p.S599Y); two were intronic point mutations (c.-32-3C>A and c.1636+5G>C) affecting mRNA processing; one was a single base deletion (c.742delC) generating a truncated protein (p.L248PfsX20). A comprehensive evaluation, based on different methodological approaches, confirmed the detrimental effect of the eight mutations on the protein and its function. Structural alterations potentially induced by the five missense mutations were also predicted through visual inspection of the atomic model of the GAA protein, in terms of both function and spatial orientation of specific residues as well as disturbance generated by amino acid substitutions. Although the remarkable heterogeneity of the mutational spectrum in Pompe disease was already known, our data demonstrate and confirm the power of molecular and functional analysis in predicting the natural course of Pompe disease.

Eight years experience with enzyme replacement therapy in two children and one adult with Pompe disease.

Pompe disease (type 2 glycogenosis, acid maltase deficiency) is a disorder affecting skeletal and cardiac muscle, caused by deficiency of acid alpha-glucosidase. In 2006 enzyme therapy with recombinant human alpha-glucosidase received marketing approval based on studies in infants. Results in older children and adults are awaited. Earlier we reported on the 3-year follow-up data of enzyme therapy in two adolescents and one adult. In the present study these patients were followed for another 5 years. Two severely affected patients, wheelchair and ventilator dependent, who had shown stabilization of pulmonary and muscle function in the first 3 years, maintained this stabilization over the 5-year extension period. In addition patients became more independent in daily life activities and quality of life improved. The third moderately affected patient had shown a remarkable improvement in muscle strength and regained the ability to walk over the first period. He showed further improvement of strength and reached normal values for age during the extension phase. The results indicate that both long-term follow-up and timing of treatment are important topics for future studies.

Methods for a prompt and reliable laboratory diagnosis of Pompe disease: report from an international consensus meeting.

Pompe disease is an autosomal recessive disorder of glycogen metabolism caused by a deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA). It presents at any age, with variable rates of progression ranging from a rapidly progressive course, often fatal by one-year of age, to a more slowly, but nevertheless relentlessly progressive course, resulting in significant morbidity and premature mortality. In infants, early initiation of enzyme replacement therapy is needed to gain the maximum therapeutic benefit, underscoring the need for early diagnosis. Several new methods for measuring GAA activity have been developed. The Pompe Disease Diagnostic Working Group met to review data generated using the new methods, and to establish a consensus regarding the application of the methods for the laboratory diagnosis of Pompe disease. Skin fibroblasts and muscle biopsy have traditionally been the samples of choice for measuring GAA activity. However, new methods using blood samples are rapidly becoming adopted because of their speed and convenience. Measuring GAA activity in blood samples should be performed under acidic conditions (pH 3.8-4.0), using up to 2 mM of the synthetic substrate 4-methylumbelliferyl-alpha-D-glucoside or glycogen (50 mg/mL), in the presence of acarbose (3-9 microM) to inhibit the isoenzyme maltase-glucoamylase. The activity of a reference enzyme should also be measured to confirm the quality of the sample. A second test should be done to support the diagnosis of Pompe disease until a program for external quality assurance and proficiency testing of the enzymatic diagnosis in blood is established.

Cardiac evaluation in children and adults with Pompe disease sharing the common c.-32-13T>G genotype rarely reveals abnormalities.

BACKGROUND AND OBJECTIVE: Pompe disease is an inherited metabolic disorder caused by deficiency of acid alpha-glucosidase. All affected neonates have a severe hypertrophic cardiomyopathy, leading to cardiac failure and death within the first year of life. We investigated the presence and extent of cardiac involvement in children and adults with Pompe disease with the common c.-32-13T>G genotype to determine the usefulness of cardiac screening in these patients with relatively 'milder' phenotypes. METHODS: Cardiac dimensions and function were evaluated through echocardiography, electrocardiography and Holter monitoring. The total group comprised 68 patients with Pompe disease, of whom 22 patients had disease onset before the age of 18. RESULTS: Two patients (3%) had cardiac abnormalities possibly related to Pompe disease: Electrocardiography showed a Wolff-Parkinson-White pattern in an 8-year-old girl, and one severely affected adult patient had a mild hypertrophic cardiomyopathy. This hypertrophy did not change during treatment with recombinant human alpha-glucosidase. In addition, four adult patients showed minor cardiac abnormalities which did not exceed the prevalence in the general population and were attributed to advanced age, hypertension or pre-existing cardiac pathology unrelated to Pompe disease. CONCLUSIONS: Cardiac involvement is rare in Pompe patients with the common c.-32-13T>G genotype. The younger patients were not more frequently affected than the adults. Electrocardiographic evaluation appears to be appropriate as initial screening tool. Extensive cardiac screening seems indicated only if the electrocardiogram is abnormal or the patient has a history of cardiac disease.

Clinical diversity in glycogenosis type II. Biosynthesis and in situ localization of acid alpha-glucosidase in mutant fibroblasts.

The molecular basis of clinical diversity in glycogenosis type II (Pompe's disease) was investigated by comparing the nature of acid alpha-glucosidase deficiency in cultured fibroblasts from 30 patients. Biosynthetic forms of acid alpha-glucosidase with different molecular mass were separated electrophoretically and identified by immunoblotting. Immuno-electron microscopy was employed to determine the intracellular localization of mutant enzyme. Our studies illustrate that maturation of acid alpha-glucosidase is associated with transport to the lysosomes. Deficiency of catalytically active mature enzyme in lysosomes is common to all clinical phenotypes but, in the majority of cases, is more profound in early onset than in late onset forms of the disease. Thus, the results suggest that the clinical course of glycogenosis type II is primarily determined by the amount of functional acid alpha-glucosidase. The role of secondary factors can, however, not be excluded because three adult patients were identified with very low activity and little enzyme in the lysosomes.

Intravenous administration of phosphorylated acid alpha-glucosidase leads to uptake of enzyme in heart and skeletal muscle of mice.

The lysosomal storage disorder glycogenosis type II is caused by acid alpha-glucosidase deficiency. In this study we have investigated the possible applicability of mannose 6-phosphate receptor-mediated enzyme replacement therapy to correct the enzyme deficiency in the most affected tissues. Bovine testes acid alpha-glucosidase containing phosphorylated mannose residues was intravenously administered to mice and found to be taken up by heart (70% increase of activity) and skeletal muscle (43% increase); the major target organs. The uptake of nonphosphorylated human placenta acid alpha-glucosidase by heart and skeletal muscle appeared to be significantly less efficient, whereas uptake of dephosphorylated bovine testes enzyme was not detectable. The phosphorylated bovine testes acid alpha-glucosidase remained present in mouse skeletal muscle up to 9-15 d after administration, with a half-life of 2-4 d. Besides being measured in skeletal muscle and heart, uptake of phosphorylated bovine testes and nonphosphorylated human placenta acid alpha-glucosidase was measured in several other organs, but not in brain. The increase of acid alpha-glucosidase activity was highest in liver and spleen. We concluded that application of mannose 6-phosphate receptor-mediated enzyme replacement therapy may offer new perspectives for treatment of glycogenesis type II.

Impact of late-onset Pompe disease on participation in daily life activities: evaluation of the Rotterdam Handicap Scale.

With the recent approval of enzyme replacement therapy for Pompe disease, insight into the social consequences of this disorder becomes even more relevant. The aim of this study was to measure the impact of late-onset Pompe disease on participation in daily life activities and to evaluate the applicability of the Rotterdam Handicap Scale (RHS) for use in Pompe disease. Two hundred fifty-seven adult patients from different countries participated in the study. The mean RHS score was 25.9+/-6.5 on a scale of 9-36. Individual item scores were lowest for 'domestic tasks indoors', 'domestic tasks outdoors', and 'work/study'. The mean RHS score differed significantly between patients with and without respiratory support (22.9 vs. 28.5, p<0.001) and patients with and without a wheelchair (20.9 vs. 29.5, p<0.001). No differences in RHS score were found between countries. The RHS showed good internal consistency and excellent Test-retest reliability. A ceiling effect of 8% was present. We conclude that the RHS seems suitable for this patient population and that Pompe disease has a large impact on the participation in daily life activities, in particular on the ability of patients to fulfil their work or study.

Seven cases of Pompe disease from Greece.

We present seven cases of Pompe disease (McKusick 232300; glycogen storage disease type II; acid maltase deficiency) from Greece. The onset of symptoms varied from early childhood to late adulthood, and the patients had quite variable duration of disease. All but one of them had muscle weakness and all had mildly to highly elevated serum creatine kinase. The diagnosis in all cases was confirmed by the finding of acid alpha-glucosidase (EC 3.2.1.3/20) deficiency in cultured skin fibroblasts. Thirteen mutant alleles were identified and nine different pathogenic mutations were encountered. Four were new: c.2071_2072insAGCCG leads to frameshift and total loss of function; c.1856G > A (p.Ser619Asn) leads to 90-95% loss of function; and the splice-site mutations c.1552-3C > G and c.2331+4A > G reduce the number of correct splicing events by more than 90%. The splice-site mutation c.-32-13T > G (IVS1-13T > G) was encountered four times and seems equally common among Greek and other caucasians. The other mutations: c.925G > A (p.Gly309Arg), c.[307T > G; 271G > A] (p.Cys103Gly; Asp91Asn), c.271del and c.1655T > C (p.Leu552Pro) have been reported earlier. Our study highlights the heterogeneity of Pompe disease in Greece and provides tools for diagnosis and carrier detection.

Clinical manifestation and natural course of late-onset Pompe's disease in 54 Dutch patients.

Late-onset Pompe's disease (acid maltase deficiency, glycogen storage disease type II) is a slowly progressive myopathy caused by deficiency of acid alpha-glucosidase. Current developments in enzyme replacement therapy require detailed knowledge of the kind and severity of symptoms and the natural course of the disease in the patient population. A detailed questionnaire covering the patients' medical history and current situation was developed and information was gathered from 54 Dutch patients. The mean age of the participants was 48.6 +/- 15.6 years. The first complaints started at a mean age of 28.1 +/- 14.3 years and were mostly related to mobility problems and limb-girdle weakness. Fifty-eight percent of the adult patients indicated the presence of mild muscular symptoms during childhood. Twenty-eight percent of the patients waited >5 years for the final diagnosis after the first visit to a physician for disease-related complaints. At the time of questionnaire completion, 48% of the study population used a wheelchair and 37% used artificial ventilation. Movements such as rising from an armchair, taking stairs or getting upright after bending over were difficult or impossible for more than two-thirds of the respondents. The age at onset, the rate of disease progression and the sequence of respiratory and skeletal muscle involvement varied substantially between patients. Seventy-six percent of the participants indicated being troubled by fatigue and 46% by pain. This survey has mapped the age at onset, presenting symptoms, heterogeneity in progression and range of disease severity in a large group of Dutch patients. We conclude that early manifestations in childhood require proper attention to prevent unnecessary delay of the diagnosis. The follow-up of patients with late-onset Pompe's disease should focus on respiratory and limb-girdle muscle function, the capacity to perform daily activities, and the presentation of fatigue and pain.

Pompe disease (glycogen storage disease type II): clinical features and enzyme replacement therapy.

Pompe disease (glycogen storage disease type II, acid maltase deficiency) is a progressive metabolic myopathy caused by deficiency of the lysosomal enzyme acid alpha-glucosidase. This leads to an accumulation of glycogen in various tissues of the body, most notably in skeletal muscle. The disease has an autosomal recessive inheritance with a predicted frequency of 1 :40.000. Pompe disease is a continuous spectrum but for clinical practice different subtypes are recognized. The classic infantile form of the disease occurs in infants (shortly after birth) and is characterized by generalized hypotonia, failure to thrive, and cardiorespiratory failure. Patients usually die within the first year of life. The non-classic or late-onset form of the disease may occur at any age in childhood or adulthood. It presents predominantly as a slowly progressive proximal myopathy, with or without respiratory failure. Enzyme replacement therapy (ERT) is under study as treatment for the disease. The first results with recombinant human alpha-glucosidase are promising and a registered therapy seems near. Beneficial effects of ERT have been reported both in patients with the classic infantile form as well as in patients with the non-classic or late-onset form of the disease. The best therapeutic results are achieved when ERT is started early in the course of symptom development and before irreversible muscular damage has occurred. Detailed knowledge about the natural course of the disease becomes more and more essential to determine the indication and timing of treatment.