Acid maltase deficiency presenting with a myopathy and exercise induced urinary incontinence in a 68 year old male

What's new and what's next for gene therapy in Pompe disease?

INTRODUCTION

Pompe disease is an autosomal recessive disorder caused by a deficiency of acid-α-glucosidase (GAA), an enzyme responsible for hydrolyzing lysosomal glycogen. A lack of GAA leads to accumulation of glycogen in the lysosomes of cardiac, skeletal, and smooth muscle cells, as well as in the central and peripheral nervous system. Enzyme replacement therapy has been the standard of care for 15 years and slows disease progression, particularly in the heart, and improves survival. However, there are limitations of ERT success, which gene therapy can overcome.

AREAS COVERED

Gene therapy offers several advantages including prolonged and consistent GAA expression and correction of skeletal muscle as well as the critical CNS pathology. We provide a systematic review of the preclinical and clinical outcomes of adeno-associated viral mediated gene therapy and alternative gene therapy strategies, highlighting what has been successful.

EXPERT OPINION

Although the preclinical and clinical studies so far have been promising, barriers exist that need to be addressed in gene therapy for Pompe disease. New strategies including novel capsids for better targeting, optimized DNA vectors, and adjuctive therapies will allow for a lower dose, and ameliorate the immune response.

Prevalence of lower urinary tract symptoms in children with early-treated infantile-onset Pompe disease: A single-centre cross-sectional study

AIM

To evaluate lower urinary tract symptoms (LUTS) in children with infantile-onset Pompe disease (IOPD) who received early treatment.

METHODS

Pompe disease (PD), or glycogen storage disease II is a rare autosomal recessive lysosomal storage disease that affects multiple organ systems. To our knowledge, only one study has focused on the relationship between LUTS and incontinence in children with PD. This cross-sectional study was conducted from August 2019 through March 2021 and children with IOPD, who had received early and regular enzyme replacement therapy, were enrolled. Participants or their parents completed the Dysfunctional Voiding Scoring System (DVSS) questionnaire. All children underwent uroflowmetry and postvoid residual urine measurements. Fourteen children (age, 4-9 years) with IOPD were enrolled.

RESULTS

Ten patients (71.4%) had abnormal uroflow curves. In addition, results of the DVSS revealed that approximately half (42.9%) of our IOPD patients had voiding dysfunction, with urinary incontinence as the most common symptom (64.3%, 9/14). No significant correlations were found between LUTS and uroflow curves in children with IOPD.

CONCLUSIONS

The frequency of LUTS and lower urinary tract dysfunction noted on uroflowmetry should encourage pediatricians to actively identify IOPD patients with LUTS, regardless of the timing and frequency of their treatments, and refer them to a urologist for further evaluation and appropriate treatment.

Glycogen accumulation in smooth muscle of a Pompe disease mouse model

Pompe disease is a lysosomal storage disease caused by mutations within the GAA gene, which encodes acid α-glucosidase (GAA)—an enzyme necessary for lysosomal glycogen degradation. A lack of GAA results in an accumulation of glycogen in cardiac and skeletal muscle, as well as in motor neurons. The only FDA approved treatment for Pompe disease—an enzyme replacement therapy (ERT)—increases survival of patients, but has unmasked previously unrecognized clinical manifestations of Pompe disease. These clinical signs and symptoms include tracheo-bronchomalacia, vascular aneurysms, and gastro-intestinal discomfort. Together, these previously unrecognized pathologies indicate that GAA-deficiency impacts smooth muscle in addition to skeletal and cardiac muscle. Thus, we sought to characterize smooth muscle pathology in the airway, vascular, gastrointestinal, and genitourinary in the Gaa^−/− mouse model. Increased levels of glycogen were present in smooth muscle cells of the aorta, trachea, esophagus, stomach, and bladder of Gaa^−/− mice, compared to wild type mice. In addition, there was an increased abundance of both lysosome membrane protein (LAMP1) and autophagosome membrane protein (LC3) indicating vacuolar accumulation in several tissues. Taken together, we show that GAA deficiency results in subsequent pathology in smooth muscle cells, which may lead to life-threatening complications if not properly treated.

The impact of Pompe disease on smooth muscle: a review

Pompe disease (OMIM 232300) is an autosomal recessive disorder caused by mutations in the gene encoding acid α-glucosidase (GAA) (EC 3.2.1.20), the enzyme responsible for hydrolyzing lysosomal glycogen. The primary cellular pathology is lysosomal glycogen accumulation in cardiac muscle, skeletal muscle, and motor neurons, which ultimately results in cardiorespiratory failure. However, the severity of pathology and its impact on clinical outcomes are poorly described in smooth muscle. The advent of enzyme replacement therapy (ERT) in 2006 has improved clinical outcomes in infantile-onset Pompe disease patients. Although ERT increases patient life expectancy and ventilator free survival, it is not entirely curative. Persistent motor neuron pathology and weakness of respiratory muscles, including airway smooth muscles, contribute to the need for mechanical ventilation by some patients on ERT. Some patients on ERT continue to experience life-threatening pathology to vascular smooth muscle, such as aneurysms or dissections within the aorta and cerebral arteries. Better characterization of the disease impact on smooth muscle will inform treatment development and help anticipate later complications. This review summarizes the published knowledge of smooth muscle pathology associated with Pompe disease in animal models and in patients.

Urge incontinence and gastrointestinal symptoms in adult patients with pompe disease: a cross-sectional survey

OBJECTIVE

To determine the frequency and impact of gastrointestinal symptoms, and bowel and urinary incontinence, as this is currently unknown in adults with Pompe disease.

METHODS

Adult German Pompe patients and age- and gender-matched controls were asked about symptoms in the upper and lower intestinal tract as well as urinary incontinence using the Gastrointestinal Symptoms Questionnaire and the International Consultation on Incontinence Questionnaires for Bowel Symptoms and Urinary Incontinence.

RESULTS

The overall response rate was 78%; 57 patients and 57 controls participated. The mean age of the patients was 48.3 years ±14.7 (28 female, 29 male). 84% of patients were receiving enzyme replacement therapy. Stool urgency, diarrhoea, and urinary urge incontinence were reported significantly more frequently in patients compared to the age- and gender-matched controls (55%, 56%, 33% vs. 20%, 18%, 7%). 20% of Pompe patients used loperamide daily against diarrhoea. No other gastrointestinal tract-related symptoms were reported to occur more frequently in Pompe patients than in controls.

CONCLUSIONS

Compared to age- and gender-matched controls, both urinary and bowel incontinence occur in a higher frequency in adults with Pompe disease and have a major impact on daily life.

The natural course of non–classic Pompe’s disease; a review of 225 published cases

Pompe's disease is a neuromuscular disorder caused by deficiency of lysosomal acid alpha-glucosidase. Recombinant human alpha- glucosidase is under evaluation as therapeutic drug. In light of this development we studied the natural course of cases not fitting the definition of classic infantile Pompe's disease. Our review of 109 reports including 225 cases shows a continuous spectrum of phenotypes. The onset of symptoms ranged from 0 to 71 years. Based on the available literature, no criteria to delineate clinical sub-types could be established.A common denominator of these cases is that first symptoms were related to or caused by muscle weakness. In general, patients with a later onset of symptoms seemed to have a better prognosis. Respiratory failure was the most frequent cause of death. CK, LDH, ASAT, ALAT and muscle glycogen levels were frequently but not always elevated. In most cases a muscle biopsy revealed lysosomal pathology, but normal muscle morphology does not exclude Pompe's disease. In 10% of the cases in which the enzyme assay on leukocytes was used, a normal alpha-glucosidase activity was reported. Data on skeletal muscle strength and function, pulmonary function, disability, handicap and quality of life were insufficiently reported in the literature. Studies of non-classic Pompe's disease should focus on these aspects, before enzyme replacement therapy becomes generally available.

Twenty-two novel mutations in the lysosomal ?-glucosidase gene (GAA) underscore the genotype-phenotype correlation in glycogen storage disease type II

Patients with glycogen storage disease type II (GSDII, Pompe disease) suffer from progressive muscle weakness due to acid alpha-glucosidase deficiency. The disease is inherited as an autosomal recessive trait with a spectrum of clinical phenotypes. We have investigated 29 cases of GSDII and thereby identified 55 pathogenic mutations of the acid alpha-glucosidase gene (GAA) encoding acid maltase. There were 34 different mutations identified, 22 of which were novel. All of the missense mutations and two other mutations with an unpredictable effect on acid alpha-glucosidase synthesis and function were transiently expressed in COS cells. The effect of a novel splice-site mutation was investigated by real-time PCR analysis. The outcome of our analysis underscores the notion that the clinical phenotype of GSDII is largely dictated by the nature of the mutations in the GAA alleles. This genotype-phenotype correlation makes DNA analysis a valuable tool to help predict the clinical course of the disease.

Pathological features of glycogen storage disease type II highlighted in the knockout mouse model

Glycogen storage disease type II (GSDII; Pompe's disease) is an autosomal recessive disease caused by lysosomal alpha-glucosidase deficiency. Skeletal muscle weakness is the most conspicuous clinical symptom of patients suffering from GSDII and skeletal muscle also is prominently involved in the knockout mouse model of this disease. Thus far, however, little detailed information has been published on the pathological changes in other mouse tissues. This paper aims to provide these data and gives a record of the clinical course of the mouse model over a 2-year period. Four-month-old affected mice perform worse in a running wheel than their unaffected littermates, but do not yet display other clear signs of disease. The lysosomal glycogen storage, already evident at birth, becomes more severe in time, leading to muscle wasting by 9-10 months of age and then limb girdle weakness and kyphosis. The disease does not markedly shorten the animal's life span despite the serious tissue pathology, which is not limited to heart and skeletal muscle, but is also seen in the smooth muscle of blood vessels and of the respiratory, digestive, and urogenital tracts. In addition, the mice have lysosomal glycogen storage in the liver, kidney, spleen, and salivary gland; in Schwann cells of the peripheral nerves, and in a subset of neurons in the central nervous system. By pathological criteria, the knockout mouse model parallels the human infantile form of GSDII and is attractive for studying the possible reversal of tissue pathology and symptomatology under different therapeutic regimes.

Clinical variability in adult-onset acid maltase deficiency: report of affected sibs and review of the literature

Acid maltase deficiency (AMD) is a rare cause of muscle disease in adult patients. The present report of 2 sibs and review of 36 previously reported cases illustrates the vast clinical variability in adult-onset AMD. This is 1 of only 3 reports to document tongue weakness and enlargement in an adult with AMD. The presenting signs and symptoms usually include progressive limb weakness, restrictive lung disease, or both. Consistent supportive abnormalities include a modest elevation in serum CK, a reduction in the forced vital capacity, and abnormal spontaneous activity (that is, myotonic discharges or fibrillations) in resting muscles during needle electromyography. The clinical spectrum is also extended to include distal limb weakness, scapular winging, asymmetric muscle weakness, and tongue involvement.