Protein turnover in acid maltase deficiency before and after treatment with a high protein diet

Omics-Based Approaches for the Characterization of Pompe Disease Metabolic Phenotypes

Lysosomal storage disorders (LSDs) constitute a large group of rare, multisystemic, inherited disorders of metabolism, characterized by defects in lysosomal enzymes, accessory proteins, membrane transporters or trafficking proteins. Pompe disease (PD) is produced by mutations in the acid alpha-glucosidase (GAA) lysosomal enzyme. This enzymatic deficiency leads to the aberrant accumulation of glycogen in the lysosome. The onset of symptoms, including a variety of neurological and multiple-organ pathologies, can range from birth to adulthood, and disease severity can vary between individuals. Although very significant advances related to the development of new treatments, and also to the improvement of newborn screening programs and tools for a more accurate diagnosis and follow-up of patients, have occurred over recent years, there exists an unmet need for further understanding the molecular mechanisms underlying the progression of the disease. Also, the reason why currently available treatments lose effectiveness over time in some patients is not completely understood. In this scenario, characterization of the metabolic phenotype is a valuable approach to gain insights into the global impact of lysosomal dysfunction, and its potential correlation with clinical progression and response to therapies. These approaches represent a discovery tool for investigating disease-induced modifications in the complete metabolic profile, including large numbers of metabolites that are simultaneously analyzed, enabling the identification of novel potential biomarkers associated with these conditions. This review aims to highlight the most relevant findings of recently published omics-based studies with a particular focus on describing the clinical potential of the specific metabolic phenotypes associated to different subgroups of PD patients.

Nutrition and exercise in Pompe disease

The current standard of care for Pompe disease (PD) is the administration of enzyme replacement therapy (ERT). Exercise and nutrition are often considered as complementary strategies rather than "treatments" per se. Nutritional assessment is important in patients with locomotor disability because the relative hypodynamia limits energy expenditure and thus the total amount of energy must be reduced to avoid obesity. A lower total energy intake often leads to lower protein and micronutrient intake. Consequently, ensuring that Pompe patients are tested for and replaced for deficiencies (protein, vitamin D, vitamin B12, etc.) is an important aspect of care. Furthermore, given the role of autophagy in the pathophysiology of PD and the fact that fasting induces autophagy, it is important that strategies such as nutritional timing and amino acid intake (L-arginine, L-leucine) be evaluated as therapies. Exercise interventions have been shown to improve six-minute walk testing distance by more than what was seen in the seminal ERT study in late-onset PD. Exercise therapy can also activate autophagy, and this is likely another component of its efficacy. The current review will evaluate the theoretical and practical aspects of nutrition and exercise as therapies for patients with PD.

Therapeutic Benefit of Autophagy Modulation in Pompe Disease

The complexity of the pathogenic cascade in lysosomal storage disorders suggests that combination therapy will be needed to target various aspects of pathogenesis. The standard of care for Pompe disease (glycogen storage disease type II), a deficiency of lysosomal acid alpha glucosidase, is enzyme replacement therapy (ERT). Many patients have poor outcomes due to limited efficacy of the drug in clearing muscle glycogen stores. The resistance to therapy is linked to massive autophagic buildup in the diseased muscle. We have explored two strategies to address the problem. Genetic suppression of autophagy in muscle of knockout mice resulted in the removal of autophagic buildup, increase in muscle force, decrease in glycogen level, and near-complete clearance of lysosomal glycogen following ERT. However, this approach leads to accumulation of ubiquitinated proteins, oxidative stress, and exacerbation of muscle atrophy. Another approach involves AAV-mediated TSC knockdown in knockout muscle leading to upregulation of mTOR, inhibition of autophagy, reversal of atrophy, and efficient cellular clearance on ERT. Importantly, this approach reveals the possibility of reversing already established autophagic buildup, rather than preventing its development.

A New Condition in McArdle Disease: Poor Bone Health-Benefits of an Active Lifestyle

INTRODUCTION-PURPOSE

McArdle disease (muscle glycogen phosphorylase deficiency) is a genetic condition associated with exercise intolerance, but how it affects lean mass (LM) and bone mineral content (BMC) and density (BMD) in patients is unknown. We compared these variables between McArdle patients and age-/sex-matched healthy controls and assessed their potential association with physical activity levels in patients.

METHODS

A case-control, cross-sectional design was used to examine LM, BMC, and BMD by using dual-energy x-ray absorptiometry in 136 young adults of both sexes (36 McArdle patients (33 ± 15 yr) and 103 controls (34 ± 11 yr)). Physical activity was assessed using the International Physical Activity Questionnaire.

RESULTS

McArdle patients had significantly lower LM values in whole-body and regional sites compared with their corresponding controls, whereas no differences were found (except for the trunk) when physically active patients (n = 23) were compared with controls. All bone-related variables were significantly lower in patients than in controls (average difference of 13% for BMC and 7.6% for BMD). By contrast, no significant differences at the lumbar spine, pelvis, and femur sites were found between physically active patients and controls.

CONCLUSIONS

We report on a previously undescribed condition in McArdle patients, poor bone health, which warrants further attention because it can occur in relatively young adults. An active lifestyle can at least partly alleviate this disorder presumably because of its beneficial effect on LM.

Pompe Disease: Diagnosis and Management. Evidence-Based Guidelines from a Canadian Expert Panel

Pompe disease is a lysosomal storage disorder caused by a deficiency of the enzyme acid alpha-glucosidase. Patients have skeletal muscle and respiratory weakness with or without cardiomyopathy. The objective of our review was to systematically evaluate the quality of evidence from the literature to formulate evidence-based guidelines for the diagnosis and management of patients with Pompe disease. The literature review was conducted using published literature, clinical trials, cohort studies and systematic reviews. Cardinal treatment decisions produced seven management guidelines and were assigned a GRADE classification based on the quality of evidence in the published literature. In addition, six recommendations were made based on best clinical practices but with insufficient data to form a guideline. Studying outcomes in rare diseases is challenging due to the small number of patients, but this is in particular the reason why we believe that informed treatment decisions need to consider the quality of the evidence.

Methods of diagnosis of patients with Pompe disease: Data from the Pompe Registry

Pompe disease is a rare, autosomal recessive disorder characterized by deficiency of lysosomal acid alpha-glucosidase and accumulation of lysosomal glycogen in many tissues. The variable clinical manifestations, broad phenotypic spectrum, and overlap of signs and symptoms with other neuromuscular diseases make diagnosis challenging. In the past, the diagnosis of Pompe disease was based on enzyme activity assay in skin fibroblasts or muscle tissue. In 2004, methods for measuring acid alpha-glucosidase activity in blood were published. To compare how diagnostic methods changed over time and whether they differed by geographic region and clinical phenotype, we examined diagnostic methods used for 1059 patients enrolled in the Pompe Registry in three onset categories (Group A: onset of signs/symptoms ≤ 12 months of age with cardiomyopathy; Group B: onset ≤ 12 months without cardiomyopathy and onset >1 year to ≤ 12 years; Group C: onset >12 years). Enzyme activity-based assays were used more frequently than other diagnostic methods. Measuring acid alpha-glucosidase activity in blood (leukocytes, lymphocytes, or dried-blood spot) increased over time; use of muscle biopsy decreased. The increased use of blood-based assays for diagnosis may result in a more timely diagnosis in patients across the clinical spectrum of Pompe disease.

Changes in nutritional status and body composition during enzyme replacement therapy in adult-onset type II glycogenosis

BACKGROUND

In adult glycogen storage disease type II (GSDII), a single-gene mutation causes reduction of the lysosomal enzyme acid alpha-glucosidse. This produces a chronic proximal myopathy with respiratory involvement. Enzyme replacement treatment (ERT) has recently become available and is expected to improve muscle strength. This should result in increased lean body mass. In this study we evaluate body composition and nutritional status in GSDII, and assess whether these parameters changed during treatment.

METHODS

Seventeen patients with late-onset GSDII, aged 52.6 +/- 16.8 years, received ERT for >18 months. Dietary habits and metabolic profiles of glucids, lipids, and proteins were assessed. Body composition was calculated using anthropometry and bioelectrical impedence analysis.

RESULTS

On inclusion, we found increased fat mass (FM) in five patients in severe disease stage; all had normal body mass index (BMI). FM correlated inversely, and lean mass (LM) directly, with creatine kinase, prealbumin and albumin levels. After treatment, BMI and FM significantly increased, while LM only showed a trend toward increase. Prealbumin and albumin levels increased as early as after the first months of ERT.

DISCUSSION

Body mass index value may underestimate FM in patients in severe stage of disease, due to altered body composition. In severely affected patients, laboratory parameters revealed a relative protein malnutrition, that was reversed by ERT, this reflecting restoration of normal muscle metabolic pathways. Increased BMI may indicate a reduction in energy consumption during exercise or respiration, along with clinical improvement.

Newborn screening for Pompe disease: synthesis of the evidence and development of screening recommendations

BACKGROUND

Pompe disease is a lysosomal storage disorder that leads to the accumulation of glycogen and subsequently to muscle weakness, organ damage, and death. Pompe disease is detectable through newborn screening, and treatment has become available recently.

OBJECTIVE

Our goal was to review systematically all available evidence regarding screening for infantile Pompe disease to help policy makers determine whether Pompe disease should be added to their state's newborn screening battery.

METHODS

We searched online databases, including Medline, clinicaltrials.gov, and the Computer Retrieval of Information on Scientific Projects database, as well as Web sites maintained by federal organizations (eg, the Food and Drug Administration) and other nonprofit or private organizations (eg, the March of Dimes and Genzyme Corp), by using the terms "glycogen storage disease type II," "Pompe disease," and "Pompe's disease." We also obtained preliminary findings from a screening program in Taiwan. Data were critically appraised and extracted by 2 investigators, one who is an expert in systematic review methods and the other who is an expert in Pompe disease.

RESULTS

The prevalence of Pompe disease has been estimated to be approximately 1 case per 40,000. Small studies suggest that enzyme therapy is highly efficacious in infantile Pompe disease and that earlier intervention leads to improved outcomes. Screening cannot distinguish between infantile and late-onset Pompe disease. The current screening program in Taiwan has a high false-positive rate; however, the threshold was purposely set low to ensure that no case would be missed.

CONCLUSIONS

Pilot studies of screening are needed to identify the most efficacious strategy for screening and determine how to manage cases of late-onset Pompe disease before screening for Pompe disease is adopted widely by newborn screening programs.

Physical therapy management of Pompe disease

Pompe disease (Glycogen storage disease type II, GSDII, or acid maltase deficiency) is an autosomal recessive disorder characterized by deficiency of acid alpha-glucosidase resulting in intra-lysosomal accumulation of glycogen and leading to progressive muscle dysfunction. The natural history of infantile-onset Pompe disease is characterized by hypertrophic cardiomyopathy and profound generalized weakness presenting in the first few months of life, with rapid progression and death usually occurring by one year of age. Late-onset Pompe disease is characterized by onset of symptoms after one year of age, less severe or absence of cardiac involvement and slower progression, with symptoms primarily related to progressive dysfunction of skeletal muscles and respiratory muscle involvement. Recent clinical trials of enzyme replacement therapy have begun to allow greater opportunity for potential improvement in motor status, function, and survival than ever before, with hopes of moving toward maximizing physical function for individuals with Pompe disease. Children are living longer with some achieving independent sitting, creeping, and walking-milestones typically never achieved in the untreated natural history of the disorder. With increased survival, clinical management based on an understanding of the pathology and pathokinesiology of motor function gains importance. This article reviews current knowledge regarding the motor system in Pompe disease and provides an overview of physical therapy management of Pompe disease, including management strategies for individuals on enzyme replacement therapy.

The effect of L-alanine therapy in a patient with adult onset glycogen storage disease type II

Adult-onset glycogen storage disease type II (GSD II) (McKusick 232300) is a progressive disabling myopathy. At present there is no treatment of proven clinical efficacy. Enzyme replacement therapy may in the future provide benefit but it will be costly and is not yet freely available. L-Alanine, a simple and relatively cheap therapy, has been shown to reduce protein degradation in GSD II patients but has not previously been assessed for clinical benefit in a controlled study. In this study L-alanine was assessed in a double blind, placebo-controlled, crossover n = 1 study. Assessments consisted of spirometry, cardiopulmonary exercise testing, quality of life measurements, biochemical markers and assessment by the criterion 4-component model of body composition. Alanine therapy was associated with a 15% gain in total body protein. However, the patient showed no functional improvement and reported feeling worse after treatment. Further controlled studies in a small group may be warranted, but not widespread use of this therapy.

Modification of the natural history of adult-onset acid maltase deficiency by nutrition and exercise therapy

Adult-onset acid maltase deficiency is an inherited lysosomal skeletal-muscle disease characterized by progressive myopathy and respiratory failure, for which there is no known therapy. In an uncontrolled, prospective study, we evaluated whether adherence to high-protein and low-carbohydrate nutrition and exercise therapy (NET) can slow the progressive deterioration of muscle function in this disease. Thirty-four patients have been treated with NET for periods of 2-10 years (mean 4.5 +/- 2.5). Pre-NET rate of muscle function deterioration, as measured by the Walton scale, was compared to post-NET rate. Twenty-six patients were deemed to be consistently compliant with NET. Difference between pre-NET slope of muscle function deterioration to that of post-NET slope in compliant patients was -0.29 (95% CI -0.19, 0.39) (P < 0.0001). We conclude that compliance with NET can slow deterioration of muscle function and improve the natural history of adult-onset acid maltase deficiency. Muscle Nerve, 2006.

Efficacy of multidisciplinary approach in the treatment of two cases of nonclassical infantile glycogenosis type II

Glycogenosis type II (GSD II) is a lysosomal storage disorder due to acid alpha-glucosidase deficiency. We report the results of a clinical multidisciplinary approach in two cases of nonclassical infantile GSD II. The patients received a high-protein diet by percutaneous enteral gastrostomy (PEG), mechanical ventilatory support by tracheostomy and a physiotherapy programme. After 12 months of treatment, the patients showed significant improvement in muscular strength, nutritional state and respiratory function. Electrocardiography (ECG) and echocardiography improved in both patients. They maintained good clinical conditions for a period of 18 and 20 months, respectively; thereafter they presented with an elevated and persistent fever that was not correlated to a septic status and was not responsive to any antipyretic treatment. They deteriorated progressively and died. This study shows how a multidisciplinary approach may be useful to improve, even if temporarily, the clinical course of nonclassical infantile GSD II.

Skeletal muscle weakness and dysphagia caused by acid maltase deficiency: nutritional consequences of coincident celiac sprue

BACKGROUND

A 30-year-old woman with celiac sprue had progressive weight loss, myalgia, limb-girdle weakness, and dysphagia.

METHODS AND RESULTS

Barium swallow showed an atonic esophagus, and scintigraphic study confirmed esophageal dysmotility. Skeletal muscle biopsy showed characteristic appearances of acid maltase deficiency, which was confirmed by a reduction of leukocyte acid alpha-glucosidase activity.

CONCLUSIONS

Nutritional factors may have accelerated the presentation of the lysosomal storage disorder. This is the first reported case of dysphagia caused by esophageal motor weakness in acid maltase deficiency.

[Myopathy in adults caused by acid maltase deficiency. A trial of treatment with high protein diet]

A 21-year old women with rhizomelic muscular deficit and signs of hypercapnia developed acute respiratory failure. Laboratory tests revealed high creatine kinase activity, and electromyograms showed myogenic patterns with a few myotonic discharges. Biopsy of the quadriceps muscle elicited major vacuolar myopathy with glycogen overload. Acid maltase activity was undetectable in muscular tissue. After 7 months on high-protein diet (1540 calories, 37% proteins) there was no clinical or biochemical improvement. The other published cases of acid maltase deficiency treated with high-protein diet are discussed.

Muscle glycogenosis

This review describes clinical, biochemical and genetic features of the four inborn errors affecting muscle glycogen breakdown, namely deficiencies of phosphorylase, phosphorylase kinase, amylo-1,6-glucosidase and acid alpha-glucosidase. They are characterized by a wide spectrum of clinical manifestation, affecting age of onset, clinical features, progress of disease and tissue involvement. Biochemically, variability of all four enzyme deficiencies is evident in terms of differences in residual enzyme present in tissues, and in the presence or absence of enzyme protein. Genetic heterogeneity, which has been documented in each of the enzyme deficiencies, manifests itself in terms of the presence, absence, quantity or size of mRNA. In phosphorylase deficiency heterogeneity has also been documented at the DNA level. In acid maltase deficiency nine mutant phenotypes have been described affecting various stages of lysosomal enzyme processing.

The effect of a high protein diet on leucine and alanine turnover in acid maltase deficiency

Leucine and alanine production rate was measured in 5 patients with acid maltase deficiency in the postabsorptive state, following 6 months on a normal diet with placebo and 6 months on an isocaloric high protein diet (16-22% protein). Whole body leucine production rate, a measure of protein degradation, expressed in terms of lean body mass was significantly greater than in five control subjects. Following the high protein diet, leucine production rate was decreased in four of the five patients but this was not statistically significant. Alanine production rate expressed in terms of lean body mass was significantly greater than in control subjects. After the high protein diet, alanine production rate and concentration were significantly decreased (p less than 0.05). There were no significant improvements in any of the clinically relevant variables measured in these patients. It is possible that a larger increase in protein intake over a longer time period may have a clinical effect.

Effects of a high-protein diet in acid maltase deficiency

The effects of a high-protein diet were studied in 5 adult cases of acid maltase deficiency. Measurements of muscle strength, pulmonary function and 3-methylhistidine excretion revealed no improvement consistently attributable to the diet.