Adult acid maltase deficiency

Development of a rapid simultaneous assay of two urinary tetrasaccharide metabolites using differential ion mobility and tandem mass spectrometry and its application to patients with glycogen storage disease (type Ib and II)

Glucose tetrasaccharide (Glc4) and maltotetraose (M4) are important biomarkers for Pompe disease and other glycogen storage diseases (GSDs). With the development of new treatments for GSDs, more specific and sensitive bioanalytical methods are needed to determine biomarkers. In recent years, differential mobility spectrometry (DMS) has become an effective analytical technique with high selectivity and specificity. This study aimed to develop an efficient analytical method for the two urinary tetrasaccharide metabolites using DMS and apply it to patients with GSDs (type Ib and II). Urine samples were directly diluted and injected into liquid chromatography-differential mobility spectrometry tandem mass spectrometry (LC-DMS-MS/MS). Chromatographic separation was performed on an Acquity™ UPLC BEH Amide column (2.1 × 50 mm, 1.7 μm) with a short gradient elution of 2.6 min. DMS-MS/MS was used to detect two urinary tetrasaccharide metabolites in a negative multiple reaction monitoring mode with isopropanol as a modifier. A total of 20 urine samples from 6 healthy volunteers and 10 patients with GSDs (type Ib and II) were collected for analysis. The method was linear over a concentration range of 0.5~100.0 µg/mL for each urinary tetrasaccharide (r≥0.99). The intra- and inter-day precision RSD% were less than 14.3%, and the accuracy RE% were in the range of -14.3~13.4%. The relative matrix effect was between 86.6 and 114.3%. No carryover or interference was observed. Patients with GSDs (type Ib and II) had significantly higher median urinary Glc4 (P=0.001) and M4 (P=0.012) excretion than healthy subjects. The developed method was simple, rapid, sensitive, and specific. It was successfully applied to healthy volunteers and patients with GSDs (type Ib and II). DMS technology greatly improved analysis efficiency and provided high sensitivity and specificity.

Guidelines for genetic testing of muscle and neuromuscular junction disorders

Despite recent advances in the understanding of inherited muscle and neuromuscular junction diseases, as well as the advent of a wide range of genetic tests, patients continue to face delays in diagnosis of sometimes treatable disorders. These guidelines outline an approach to genetic testing in such disorders. Initially, a patient's phenotype is evaluated to identify myopathies requiring directed testing, including myotonic dystrophies, facioscapulohumeral muscular dystrophy, oculopharyngeal muscular dystrophy, mitochondrial myopathies, dystrophinopathies, and oculopharyngodistal myopathy. Initial investigation in the remaining patients is generally a comprehensive gene panel by next-generation sequencing. Broad panels have a higher diagnostic yield and can be cost-effective. Due to extensive phenotypic overlap and treatment implications, genes responsible for congenital myasthenic syndromes should be included when evaluating myopathy patients. For patients whose initial genetic testing is negative or inconclusive, phenotypic re-evaluation is warranted, along with consideration of genes and variants not included initially, as well as their acquired mimickers.

Three-dimensional tissue-engineered human skeletal muscle model of Pompe disease

In Pompe disease, the deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA) causes skeletal and cardiac muscle weakness, respiratory failure, and premature death. While enzyme replacement therapy using recombinant human GAA (rhGAA) can significantly improve patient outcomes, detailed disease mechanisms and incomplete therapeutic effects require further studies. Here we report a three-dimensional primary human skeletal muscle ("myobundle") model of infantile-onset Pompe disease (IOPD) that recapitulates hallmark pathological features including reduced GAA enzyme activity, elevated glycogen content and lysosome abundance, and increased sensitivity of muscle contractile function to metabolic stress. In vitro treatment of IOPD myobundles with rhGAA or adeno-associated virus (AAV)-mediated hGAA expression yields increased GAA activity and robust glycogen clearance, but no improvements in stress-induced functional deficits. We also apply RNA sequencing analysis to the quadriceps of untreated and AAV-treated GAA-/- mice and wild-type controls to establish a Pompe disease-specific transcriptional signature and reveal novel disease pathways. The mouse-derived signature is enriched in the transcriptomic profile of IOPD vs. healthy myobundles and partially reversed by in vitro rhGAA treatment, further confirming the utility of the human myobundle model for studies of Pompe disease and therapy.

Elevated Creatine Kinase in a 6-Year-Old Boy

Paucisymptomatic or asymptomatic but persistently elevated serum creatine kinase is not an uncommon pediatric neurology referral question. The challenge is in promptly identifying etiologies with specific treatments, even if they are rare. The presenting features for a child or adolescent with juvenile-onset Pompe disease (JOPD) can be nonspecific and heterogeneous. Clinical manifestations can appear at any age after 2 years and before adulthood, with insidious onset of symptoms related to slowly progressive skeletal or respiratory muscle weakness. This reported case highlights the importance of screening for JOPD in children with "hyper-CK-emia." Dried blood spot measuring acid α-glucosidase enzyme activity is reliable, rapid, noninvasive, and inexpensive, allowing early diagnosis. Diagnosis of JOPD is important as enzyme replacement therapy with alglucosidase alpha, an intravenous recombinant α-glucosidase, is available, and early treatment improves muscle function, quality of life, and long-term survival.

Three cases of multi-generational Pompe disease: Are current practices missing diagnostic and treatment opportunities?

Pompe disease (Glycogen storage disease type II, GSDII, or acid maltase deficiency) is an autosomal recessive metabolic myopathy with a broad clinical spectrum, ranging from infantile to late-onset presentations. In 2015, Pompe disease was added as a core condition to the Recommended Uniform Screening Panel for state newborn screening (NBS). The clinical importance of Pompe disease is evolving with the use of NBS, increasing awareness of the disease, and higher than previously reported disease prevalence; however, current practices miss additional diagnostic and potential treatment opportunities in close relatives of the family proband. In this report, we describe three families with multiple individuals in multiple generations affected by both infantile and late-onset clinical presentations of Pompe disease. The presence of multi-generational disease within these families highlights the importance of subsequent risk assessment through medical history and physical examination, with a low threshold for the screening of a proband's family members. We recommend enzymology (GAA activity assay) as the first screening method, as opposed to targeted mutation analysis, for at-risk family members. Given that the initial symptoms of the slowly progressive late-onset presentation of Pompe disease may be mild or non-specific, enzymatic testing of all parents of affected infants should be considered.

First clinical and genetic description of a family diagnosed with late-onset Pompe disease from Costa Rica

Glycogen storage disease type II, also known as Pompe disease, is an autosomal recessive disorder caused by deficiency of enzymatic activity of acid alpha-glucosidase. The wide phenotypical variation of this disease relates to the amount of residual enzymatic activity depending on the combination of mutations on each allele. We confirmed Pompe disease in a patient that presented with progressive weakness, recurrent episodes of respiratory failure associated with pneumonia, a predominantly demyelinating mixed sensorimotor polyneuropathy and paraspinal complex repetitive discharges. Genetic analysis of the GAA gene from this patient revealed two pathogenic compound heterozygous mutations: c.-32-13T>G (rs386834236, intronic), c.2560C>T (rs121907943, p.Arg854Ter); and one variant of unknown significance: c.1551+42G>A (rs115427918, intronic). We found expected mutations in two siblings and two nieces. Genetic variants reported in this family reflect on the European and African ancestry that we carry in our Costa Rican population.

New mutations and genotype-phenotype correlation in late-onset Pompe patients

Pompe disease is a glycogen storage disease caused by acid alfa-glucosidase deficiency. Here, we report clinical properties, genetic features of our late-onset Pompe patients. Seven patients were followed during the last 10 years in our institute. The clinical and laboratory findings were reviewed. Neuropsychological evaluation was performed in four patients. Myotonic discharges of paraspinal muscles and denervation potentials were seen in all patients at the diagnosis and were disappeared during follow-up in two. Only one patient, whose MRI showed cerebral atrophy, had attention and executive dysfunction. Compound heterozygous patients with IVS 1-13T>G have a milder disease. One patient who has homozygous IVS 1-13T>G mutation had more severe disease. Two of our patients who had very severe and fatal disease course carry double mutations on both alleles (c.547-39T>G and c.858+5ins7) that previously scored as "unknown" in Erasmus Pompe Center database. Lastly, we found new mutations (c.1209 C>A, 2737dupG) in two patients carrying IVS 1-13T>G in the other allele. Systemic involvements are very rare in late-onset Pompe patients. Similarly, Pompe disease does not cause cognitive impairment in adult population. Homozygous IVS 1-13T>G mutation and c.547-39T>G mutation which are previously noted as "unknown" pathogenicities cause a more severe disease.

The emerging phenotype of late-onset Pompe disease: A systematic literature review

BACKGROUND

Pompe disease is an autosomal recessive disorder caused by deficiency of the lysosomal glycogen-hydrolyzing enzyme acid α-glucosidase (GAA). The adult-onset form, late-onset Pompe disease (LOPD), has been characterized by glycogen accumulation primarily in skeletal, cardiac, and smooth muscles, causing weakness of the proximal limb girdle and respiratory muscles. However, increased scientific study of LOPD continues to enhance understanding of an evolving phenotype.

PURPOSE

To expand our understanding of the evolving phenotype of LOPD since the approval of enzyme replacement therapy (ERT) with alglucosidase alfa (Myozyme™/Lumizyme™) in 2006.

METHODS

All articles were included in the review that provided data on the charactertistics of LOPD identified via the PubMed database published since the approval of ERT in 2006. All signs and symptoms of the disease that were reported in the literature were identified and included in the review.

RESULTS

We provide a comprehensive review of the evolving phenotype of LOPD. Our findings support and extend the knowledge of the multisystemic nature of the disease.

CONCLUSIONS

With the advent of ERT and the concurrent increase in the scientific study of LOPD, the condition once primarily conceptualized as a limb-girdle muscle disease with prominent respiratory involvement is increasingly recognized to be a condition that results in signs and symptoms across body systems and structures.

Electromyographic findings in 37 patients with adult-onset acid maltase deficiency

INTRODUCTION

In acid maltase deficiency (AMD), electrical myotonia (EM) may be restricted to paraspinal muscles. A comprehensive description of the electromyographic (EMG) findings in AMD is lacking. The purpose of this study is to describe the EMG features in adult-onset AMD, focusing on the distribution of EM.

METHODS

A retrospective chart review of AMD patients diagnosed at Mayo Clinic over age 18 years.

RESULTS

Thirty-seven patients were included. Twenty-eight (76%) had EM in at least 1 muscle, and EM was more common in paraspinal and proximal limb muscles. The tensor fasciae latae (TFL) was equally sensitive to the paraspinals for EM. Three of 4 patients had EM identified in the diaphragm.

CONCLUSIONS

Approximately three-quarters of adult-onset AMD patients display EM on EMG. The paraspinal muscles and TFL are the most likely to demonstrate EM, and EM can be detected in the diaphragm of adult onset AMD patients.

Distal myopathies

In this article, distal myopathy syndromes are discussed. A discussion of the more traditional distal myopathies is followed by discussion of the myofibrillar myopathies. Other clinically and genetically distinctive distal myopathy syndromes usually based on single or smaller family cohorts are reviewed. Other neuromuscular disorders that are important to recognize are also considered, because they show prominent distal limb weakness.

Pearls & Oy-sters: clues to the diagnosis of adult-onset acid maltase deficiency

Adult-onset Pompe disease (acid maltase deficiency, glycogen storage disease type II) should be considered in the differential diagnosis in the adult patient presenting with slowly progressive selective lower extremity weakness, specifically of the hip flexors. Hip flexion weakness may be the only finding in the earliest stages of this disease. EMG findings of myotonic discharges occurring predominately in the lower extremities or paraspinal muscles, in combination with the clinical presentation, is a clue to the diagnosis of late-onset Pompe disease. Testing of all 3 paraspinal muscle levels may be useful in an otherwise normal EMG when Pompe disease is suspected.

Phenotypical variation within 22 families with Pompe disease

Background

Pompe disease has a broad clinical spectrum, in which the phenotype is partially explained by the genotype. The aim of this study was to describe phenotypical variation among siblings with non-classic Pompe disease. We hypothesized that siblings and families with the same genotype share more similar phenotypes than the total population of non-classic Pompe patients, and that this might reveal genotype-phenotype correlations.

Methods

We identified all Dutch families in which two or three siblings were diagnosed with Pompe disease and described genotype, acid α-glucosidase activity, age at symptom onset, presenting symptoms, specific clinical features, mobility and ventilator dependency.

Results

We identified 22 families comprising two or three siblings. All carried the most common mutation c.-32-13 T > G in combination with another pathogenic mutation. The median age at symptom onset was 33 years (range 1–62 years). Within sibships symptom onset was either in childhood or in adulthood. The median variation in symptom onset between siblings was nine years (range 0–31 years). Presenting symptoms were similar across siblings in 14 out of 22 families. Limb girdle weakness was most frequently reported. In some families ptosis or bulbar weakness were present in all siblings. A large variation in disease severity (based on wheelchair/ventilator dependency) was observed in 11 families. This variation did not always result from a difference in duration of the disease since a third of the less affected siblings had a longer course of the disease. Enzyme activity could not explain this variation either. In most families male patients were more severely affected. Finally, symptom onset varied substantially in twelve families despite the same GAA genotype.

Conclusion

In most families with non-classic Pompe disease siblings share a similar phenotype regarding symptom onset, presenting symptoms and specific clinical features. However, in some families the course and severity of disease varied substantially. This phenotypical variation was also observed in families with identical GAA genotypes. The commonalities and differences indicate that besides genotype, other factors such as epigenetic and environmental effects influence the clinical presentation and disease course.

Screening for later-onset Pompe's disease in patients with paucisymptomatic hyperCKemia

BACKGROUND

Pompe's disease is an inherited metabolic myopathy caused by acid α-glucosidase deficiency. Early diagnosis optimizes the treatment effectiveness.

METHODS

One-hundred-thirty-seven consecutive patients with unexplained hyperCKemia underwent the assessment of acid α-glucosidase activity on dried blood spot. Second tier confirmatory testing in positive patients included the assessment of α-glucosidase activity on lymphocytes or muscle tissue and molecular analysis.

RESULTS

Three patients were diagnosed with later-onset Pompe's disease, revealing 2.2% prevalence in asymptomatic hyperCKemia. Moreover, three patients positive to the screening revealed abnormal biochemical second tier testing, but were heterozygous for the common c.-32-13T>G mutation at molecular level.

CONCLUSIONS

The selective screening for later-onset Pompe's disease in asymptomatic hyperCKemia allowed the identification of affected patients in a pre-clinical stage. Additionally, the identification of carriers with biochemical alterations related to Pompe's disease extends the spectrum of its manifestations to heterozygous subjects.

Electrodiagnosis in neuromuscular disease

Electromyography (EMG) is an important diagnostic tool for the assessment of individuals with various neuromuscular diseases. It should be an extension of a thorough history and physical examination. Some prototypical characteristics and findings of EMG and nerve conduction studies are discussed; however, a more thorough discussion can be found in the textbooks and resources sited in the article. With an increase in molecular genetic diagnostics, EMG continues to play an important role in the diagnosis and management of patients with neuromuscular diseases and also provides a cost-effective diagnostic workup before ordering a battery of costly genetic tests.

Scapuloperoneal muscular dystrophy phenotype due to TRIM32-sarcotubular myopathy in South Dakota Hutterite

Scapuloperoneal muscular dystrophy is a group of genetically heterogeneous disorders that share the phenotype of progressive weakness of scapular and anterior distal leg muscles. Recessive mutations in C-terminal domains of TRIM32 result in limb-girdle muscular dystrophy 2H and sarcotubular myopathy, a rare congenital myopathy commonly seen in Hutterites. A scapuloperoneal phenotype has never been reported in sarcotubular myopathy. We here report a 23-year-old Hutterite man with a one-year history of progressive weakness predominantly involving the anterior tibial and left scapular muscles, and hyperCKemia. Biopsy of the anterior tibial muscle showed an active myopathy with non-rimmed vacuoles and mild denervation atrophy associated with reinnervation. The vacuoles are similar to those described in sarcotubular myopathy. TRIM32 sequencing revealed the common c.1459G>A mutation at homozygosity. A search for mutations in TRIM32 should be considered in patients with scapuloperoneal muscular dystrophy, and especially in patients of Hutterite origin or with an atypical vacuolar myopathy.

Autopsy findings in late-onset Pompe disease: a case report and systematic review of the literature

BACKGROUND

Late-onset Pompe disease (LOPD) is a rare cause of declining proximal muscle strength and respiratory function that can also affect other organ systems. The development of enzyme replacement therapy has made it one of the few inherited muscle disorders with treatment, but clinical response is difficult to assess due to the variable and often slow progression of illness. A better understanding of the disease's systemic effects can be gleaned through autopsy findings.

PURPOSE

The purpose of this study was to: (1) describe the histological findings observed in LOPD, (2) provide correlations between reported histological and clinical findings, and (3) review the literature on autopsy findings in LOPD.

METHODS

Histological evaluation of autopsy tissues from a 62-year-old woman with LOPD was conducted. A clinical history was obtained by review of the medical records. The literature was reviewed for previously reported histological and clinical findings in LOPD. Based on this case report and information from prior publications, histological and clinical findings for the disease were correlated.

RESULTS

Histologic examination revealed mostly mild vacuolar myopathy typical of glycogen accumulation within skeletal and smooth muscle cells. The most prominent vacuolar myopathy was in quadriceps muscle, which also exhibited chronic myositis with degenerating and regenerating muscle fibers. Transmission electron microscopy disclosed lysosomal glycogen accumulation within skeletal, cardiac, and vascular smooth muscle cells, correlating with published case reports of basilar artery and ascending aortic aneurysms and carotid artery dissection. Organs containing smooth muscle cells (the bladder, intestine, and esophagus) were also affected, explaining reports of symptoms such as urinary incontinence and dysphagia. In addition to glycogen accumulation, there was obvious damage to the contraction apparatus of myofibrils within cardiac and skeletal muscle cells. These histological and ultrastructural findings correlate with the clinical manifestations of LOPD.

CONCLUSIONS

This study is the first to describe histological findings of LOPD utilizing both traditional paraffin-processed tissues and epoxy resin embedded tissues for high-resolution light microscopy. The findings are similar to those seen in previous studies, but with improved morphological detail and glycogen preservation. This patient exhibited histological involvement of multiple organs, correlating with the clinical features of LOPD. With the advent of definitive therapy for Pompe disease, it is important to be aware of these findings and use them to develop methods for tracking therapeutic response.

Consensus treatment recommendations for late-onset Pompe disease

INTRODUCTION

Pompe disease is a rare, autosomal recessive disorder caused by deficiency of the glycogen-degrading lysosomal enzyme acid alpha-glucosidase. Late-onset Pompe disease is a multisystem condition, with a heterogeneous clinical presentation that mimics other neuromuscular disorders.

METHODS

Objective is to propose consensus-based treatment and management recommendations for late-onset Pompe disease.

METHODS

A systematic review of the literature by a panel of specialists with expertise in Pompe disease was undertaken.

CONCLUSIONS

A multidisciplinary team should be involved to properly treat the pulmonary, neuromuscular, orthopedic, and gastrointestinal elements of late-onset Pompe disease. Presymptomatic patients with subtle objective signs of Pompe disease (and patients symptomatic at diagnosis) should begin treatment with enzyme replacement therapy (ERT) immediately; presymptomatic patients without symptoms or signs should be observed without use of ERT. After 1 year of ERT, patients' condition should be reevaluated to determine whether ERT should be continued.

Diagnostic criteria for late-onset (childhood and adult) Pompe disease

The diagnosis of late-onset (childhood and adult) Pompe disease can often be challenging, as it is a rare disease and the heterogeneous clinical presentation can mimic the presentation of other neuromuscular disorders. The objective was to develop a consensus-based algorithm for the diagnosis of late-onset Pompe disease. A systematic literature search was conducted, and an expert panel composed of neuromuscular specialists and individuals with expertise in Pompe disease reviewed the literature and convened for consensus development. An algorithm for the diagnosis of late-onset Pompe disease was created. Patients presenting with either a limb-girdle syndrome or dyspnea secondary to diaphragm weakness should undergo further testing, including evaluations of muscle strength, motor function, and pulmonary function. A blood-based acid alpha-glucosidase (GAA) enzyme activity assay is the recommended tool to screen for GAA enzyme deficiency. The diagnosis should be confirmed by a second test: either a second GAA enzyme activity assay in another tissue or GAA gene sequencing.

Pompe disease: a review of the current diagnosis and treatment recommendations in the era of enzyme replacement therapy

Pompe disease, or glycogen storage disease type II, is a rare autosomal recessive disorder caused by mutations in the gene that encodes for alpha-glucosidase. Presentation in infancy is associated with respiratory failure, cardiomyopathy, and severe muscle weakness. Juvenile- or adult-onset cases typically present with proximal muscle weakness and are associated with respiratory insufficiency or exertional dyspnea. Treatment, until recently, was focused on supportive measures, and infants diagnosed with Pompe disease usually died within the first year of life. The recent development of recombinant alpha-glucosidase has dramatically improved the life expectancy and quality of life of infantile-onset disease with improvements in respiratory and motor function observed in juvenile- or adult-onset cases. This review focuses on the presentation, pathogenesis, diagnosis, and treatment recommendations for Pompe disease in this new era of enzyme replacement therapy.

Sibling phenotype concordance in classical infantile Pompe disease

Pompe disease (acid-alpha-glucosidase deficiency) encompasses a clinical spectrum, ranging from severe infantile-onset disease with clinical symptoms appearing before 1 year of age with rapid progression to an early death, to late-onset disease with a much more variable age at onset and disease course. Sibling phenotype discordance has been reported for late-onset Pompe disease, but has not been studied in classical infantile disease. We reviewed the medical literature for affected sibships in which at least one sibling had clinical and pathology or biochemical findings consistent with infantile Pompe disease including symptoms beginning in infancy, early hypotonia, cardiomegaly documented by 6 months of age, and early death. The age at symptom onset, age at death, and clinical course were compared between probands and affected siblings. Our results showed that since 1931, publications document 13 families with 31 affected infants (11 probands; 20 affected siblings). The median age at symptom onset for all affected infants was 3 months (range 0-6 months) with significant correlation (R = 0.60, P = 0.04) between probands and affected siblings. The median age at death for all affected infants was 6 months (range 1.5-13 months); probands were slightly older at death than their siblings. The median length of disease course for all affected infants was 3 months (0-10 months) and was slightly longer for probands. Unlike late-onset Pompe disease, there appears to be minimal phenotypic and lifespan variation among siblings with infantile Pompe disease. This prognostic information is vital for families with affected infants and allows for appropriate genetic counseling.

Polyglucosan body disease myopathy: An unusual presentation

Polyglucosan body disease (PBD) is a slowly progressive adult-onset glycogen storage disorder that typically affects upper and lower neurons. Myopathy, as a complication of PBD has been reported rarely and clinically manifests as chronic limb-girdle muscle weakness. We report an unusual case of PBD myopathy presenting as an asymmetric motor syndrome that clinically overlapped with amyotrophic lateral sclerosis, further expanding the phenotype of this disorder.

The role of different EMG methods in evaluating myopathy

For the diagnosis of myopathy, EMG may have an important role along with blood tests, muscle biopsies and genetic testing. This review evaluates different EMG methods in the diagnosis of myopathy. These include manual analysis of individual motor unit potentials and multi-motor unit potential analysis sampled at weak effort. At high effort, turns-amplitude analyses such as the cloud analysis and the peak ratio analysis have a high diagnostic yield. The EMG can seldom be used to differentiate between different types of myopathy. In the channelopathies, myotonia, exercise test and cooling of the muscle are helpful. Macro-EMG, single-fibre EMG and muscle fibre conduction velocity analysis have a limited role in myopathy, but provide information about the changes seen. Analysis of the firing rate of motor units, power spectrum analysis, as well as multichannel surface EMG may have diagnostic potential in the future. EMG is of great importance in the diagnosing of patients with myopathy, preferably a needle electrode and quantitative analyses should be used. A combination of a method at weak effort as well as a method at stronger effort seems optimal.

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.

Muscle MRI in adult-onset acid maltase deficiency

We report the spectrum of muscle involvement on magnetic resonance imaging in 11 patients with a molecularly confirmed diagnosis of adult-onset acid maltase deficiency at different clinical stages. Muscle magnetic resonance imaging showed a selective progressive pattern of muscle involvement with a constant involvement of the adductor magnus and semimembranosus at the early stage of the disease and a later fatty infiltration of the long head of the biceps femoris, semitendinosus and of the anterior thigh muscles. In the advanced phases a selective sparing of sartorius, rectus, and gracilis muscles and peripheral portions of the vastus lateralis was also evident. Muscle strength and magnetic resonance imaging findings were positively correlated. The results suggest that muscle magnetic resonance imaging may provide valuable diagnostic guidance for the assessment of accurate selective muscular involvement in acid maltase deficiency and may help monitor the progression of the disorder. Further control studies in a larger cohort are needed to evaluate the specificity of these findings.

Myopathies

Electrodiagnostic studies are an important adjunct to the clinical examination of a patient with a suspected myopathy; however, the clinical examination is crucial in making an accurate diagnosis, because electrodiagnostic studies have only a limited role in delineating with certainty the underlying myopathic disorder. Hereditary and acquired myopathies are reviewed in this article, with particular emphasis on distinguishing clinical and electrodiagnostic features. The hereditary myopathies that are discussed include the muscular dystrophies and the congenital distal mitochondrial, and metabolic myopathies. Acquired myopathies, including inflammatory, endocrine, and toxic myopathies, as well as those associated with systemic illness, are briefly reviewed.

Impaired performance of skeletal muscle in alpha-glucosidase knockout mice

Glycogen storage disease type II (GSD II) is an inherited progressive muscle disease in which lack of functional acid alpha-glucosidase (AGLU) results in lysosomal accumulation of glycogen. We report on the impact of a null mutation of the acid alpha-glucosidase gene (AGLU(-/-)) in mice on the force production capabilities, contractile mass, oxidative capacity, energy status, morphology, and desmin content of skeletal muscle. Muscle function was assessed in halothane-anesthetized animals, using a recently designed murine isometric dynamometer. Maximal torque production during single tetanic contraction was 50% lower in the knockout mice than in wild type. Loss of developed torque was found to be disproportionate to the 20% loss in muscle mass. During a series of supramaximal contraction, fatigue, expressed as percentile decline of developed torque, did not differ between AGLU(-/-) mice and age-matched controls. Muscle oxidative capacity, energy status, and protein content (normalized to either dry or wet weight) were not changed in knockout mice compared to control. Alterations in muscle cell morphology were clearly visible. Desmin content was increased, whereas alpha-actinin was not. As the decline in muscle mass is insufficient to explain the degree in decline of mechanical performance, we hypothesize that the large clusters of noncontractile material present in the cytoplasm hamper longitudinal force transmission, and hence muscle contractile function. The increase in muscular desmin content is most likely reflecting adaptations to altered intracellular force transmission.

Electrophysiological findings in X-linked myopathy with excessive autophagy

We report electrophysiological features and magnetic resonance imaging muscle findings in 4 patients and 1 female carrier of X-linked myopathy with excessive autophagy. Motor units were polyphasic with high mean amplitude and normal duration. The thigh muscles were most severely involved, but myotonic discharges were abundant in both clinically affected and unaffected muscles. Along with the clinicopathological features, these electrophysiological findings distinguish X-linked myopathy with excessive autophagy from other limb-girdle myopathies.

Clinical and genetic aspects of distal myopathies

Although most muscle disorders produce proximal weakness, some myopathies may manifest predominantly or exclusively distal weakness. Although several congenital, inflammatory, or metabolic myopathies may produce mainly distal weakness, there are several distinct entities, typically referred to as distal myopathies. Most of these are inherited conditions. The distal myopathies are rare, but characteristic clinical and histological features aid in their identification. Advances in molecular genetics have led to the identification of the gene lesions responsible for several of these entities and have also expanded our understanding of the genetic relationships of distal myopathies to other inherited disorders of muscle. This review summarizes current knowledge of the clinical and molecular aspects of the distal myopathies.

Pulmonary dysfunction in adults with nephropathic cystinosis

OBJECTIVE

To characterize the pulmonary dysfunction in patients with nephropathic cystinosis after renal transplantation.

DESIGN

Cross-sectional analysis of consecutive adult patients.

PATIENTS

Twelve adult, nephropathic cystinosis patients and 3 adult, ocular, nonnephropathic cystinosis patients admitted to the National Institutes of Health Clinical Center.

RESULTS

The 12 nephropathic cystinosis patients (age range, 21 to 40 years) showed an extraparenchymal pattern of restrictive lung disease, with inspiratory and expiratory dysfunction. Specifically, the mean FVC was 58% of predicted, the mean FEV(1) was 57% of predicted, and the mean total lung capacity was 66% of predicted, while the mean residual volume was normal. Furthermore, the mean maximal inspiratory pressure for the eight patients tested was 40% of predicted, and the mean maximal expiratory pressure was 26% of predicted. Two patients died of respiratory insufficiency. All the patients had lived at least 17 years, while lacking compliant cystine-depleting therapy with oral cysteamine. Seven patients had a conical chest, restricting excursion, and 10 of the 12 patients had evidence of the myopathy that typifies late cystinosis. In fact, the severity of pulmonary disease correlated directly with the severity of myopathy in our group of 12 patients. In contrast, the lung parenchyma was essentially normal, as gauged by chest radiographs and CT scans of the lung. The three patients with nonnephropathic cystinosis displayed entirely normal pulmonary function.

CONCLUSION

The distal myopathy characteristic of nephropathic cystinosis results in an extraparenchymal pattern of restrictive lung disease in adults who have not received long-term cystine depletion. Whether or not oral cysteamine therapy can prevent this complication remains to be determined.

Unusual clinical presentations in patients harboring the facioscapulohumeral dystrophy 4q35 deletion

Facioscapulohumeral dystrophy (FSHD) is a dominantly inherited myopathy usually associated with a deletion at locus 4q35. Typically, FSHD patients present with a recognizable constellation of signs including weakness of facial, shoulder and pelvic girdle, humeral, and anterior foreleg muscles; preservation of some muscles including the deltoids; and other characteristic features including prominent scapular winging, anterior axillary folds, and horizontally positioned clavicles. We performed clinical and FSHD genetic studies on four patients with atypical clinical features who were cared for at a regional neuromuscular center. The four patients, each harboring 4q35 deletions, presented with atypical phenotypes including facial-sparing scapular myopathy, limb-girdle muscular dystrophy, distal myopathy, and asymmetric brachial weakness. This report demonstrates the expanding clinical heterogeneity in patients harboring the 4q35 deletion.

Phenotypic expression of late-onset glycogen storage disease type II: identification of asymptomatic adults through family studies and review of reported families

The intrafamilial variability of late-onset glycogen storage disease type II was studied in siblings of 18 patients and in reports in the literature. Siblings of seven of the 18 index cases opted for DNA testing or enzyme studies after being informed by the index case of the availability of testing, and after genetic counselling. Of the 12 siblings tested, five asymptomatic individuals were diagnosed (mean age, 32.8 years; range, 17-53). Intrafamilial variability in the age at onset (more than 10 years difference) or in the clinical symptoms was found in one of seven sibships tested in this study, and also in seven sibships reported in the literature. We advocate that testing should not be offered to healthy siblings of late-onset glycogen storage disease type II patients as a routine, because it is impossible to give a precise prognosis to an individual who is symptom-free, but has been identified with a glycogen storage disease type II genotype, nor is there any therapeutic intervention available.

Congenital and metabolic myopathies of childhood or adult onset

OBJECTIVES

To investigate the clinical presentation, histological findings, and outcome of patients with congenital and metabolic myopathies (CM and MM) in whom the disease was diagnosed in childhood or adulthood.

PATIENTS AND METHODS

We reviewed the diagnosis of all skeletal muscle biopsies performed by our group between 1984 and 1996 (13 years). All patients with CM and MM of childhood or adult onset were included in the study. Patients with mitochondrial myopathies were excluded because they are multisystemic disorders with a more distinct picture than that observed in other MM. We retrospectively reviewed the clinical history, with special emphasis on the clinical patterns of presentation, histological findings, and outcome.

RESULTS

Among 1,865 biopsies, 28 (1.5%) fulfilled the diagnostic criteria for CM (seven nemaline myopathies, four multicore myopathies, three centronuclear myopathies) or MM (five adult-onset acid maltase deficiency, three myophosphorylase deficiency, three phosphofructokinase deficiency, two carnitine palmitoyl transferase deficiency, and one carnitine deficiency). In nearly half of the patients, mild stable weakness was the major complaint, whereas in one third muscular symptoms were intermittent and related to exercise. In a small number of cases, a persistently raised serum creatine kinase in an asymptomatic patient was the reason for muscle biopsy. Histological examination of skeletal muscle was highly indicative of a specific muscle disease in 26 of the 28 cases. After a mean follow-up of 7 years, the outcome has generally been good, and in most patients the myopathy did not worsen, most remaining ambulatory.

CONCLUSION

CM and MM presenting in childhood or adulthood are infrequent; the symptoms are usually mild or moderate, and the prognosis generally is good.

FSH dystrophy 4q35 deletion in patients presenting with facial-sparing scapular myopathy

OBJECTIVE

To evaluate the incidence of the facioscapulohumeral dystrophy (FSHD) 4q35 deletion in patients with facial-sparing scapular myopathy.

BACKGROUND

Scapular winging is typical of FSHD but may also be prominent in other muscle disorders including scapuloperoneal syndromes. With DNA testing, it is possible to determine if patients with facial-sparing scapular myopathy have FSHD.

METHODS

Fourteen of 17 unrelated patients with facial-sparing scapular myopathy, seen over a 7-year period at a regional neuromuscular center, agreed to have DNA testing for FSHD. The clinical and laboratory features of these patients were also noted.

RESULTS

Of the 14 patients, 10 (71%) had restriction fragments consistent with the 4q35 deletion. The mean size of the smaller fragment following EcoRI digestion was 29.5 kb (range 20 to 39). The mean age at onset was 19.9 years; at presentation, 44.7 years. Except for the absence of facial weakness, most patients had clinical and laboratory features otherwise consistent with FSHD. Five patients (50%) had a positive family history of similar weakness. Following removal of outliers, the Pearson correlation coefficient (r) value between EcoRI fragment size and age at onset was 0.64, and between fragment size and limb muscle strength, 0.64.

CONCLUSION

The FSHD 4q35 deletion was found in 71% of the facial-sparing scapular myopathy patients. They otherwise resemble typical FSHD patients in age at onset, physical characteristics, and association between fragment size and disease severity.

McArdle's disease presenting with asymmetric, late-onset arm weakness

McArdle's disease or myophosphorylase deficiency is one of the most common muscle glycogenoses and typically presents in childhood or adolescence with exercise intolerance, myalgia, myoglobinuria, and cramps in exercising muscle. We describe an elderly man who developed asymmetric proximal arm weakness at age 73. He had no history of exercise-induced cramps, myalgias, or myoglobinuria. Creatine kinase levels were elevated, serum lactate did not rise on ischemic exercise testing, and muscle biopsy showed a vacuolar myopathy with absent myophosphorylase activity. This unusual case demonstrates that McArdle's disease may present with fixed, asymmetric proximal weakness at an advanced age and should be considered in this clinical setting, especially when a history of poor exercise tolerance can be elicited.

Acid maltase deficiency and related myopathies

There are 11 glycogen diseases (GSD), nine of which are associated with myopathy. Most of these glycogen storage myopathies are associated with dynamic symptoms and signs in that the major neuromuscular complaints are exercise-induced muscle pain, cramps, and myoglobinura (e.g., GSD V or McArdle's disease associated with myophosphorylase deficiency). The other types of glycogen storage myopathies are considered static in that they are associated with fixed weakness rather than dynamic symptoms and signs. The static glycogen storage myopathies include: GSD I or Pompe's disease (acid maltase or (-glucosidase deficiency), GSD II or Cori-Forbes disease (debranching enzyme deficiency), and GSD IV or Andersen's disease (branching enzyme deficiency). This article reviews the clinical, laboratory, electrophysiologic, histopathologic, and pathogenesis of these static GSD myopathies.

Cervicomedullary astrocytoma simulating a neuromuscular disorder

A 12-year-old male developed progressive proximal upper extremity weakness over a 3- to 4-year period. The clinical findings of proximal upper extremity weakness and atrophy, prominent scapular winging, and no sensory deficits or upper motor neuron signs suggested a neuromuscular disorder. Electromyography was consistent with a chronic denervating disorder involving the upper cervical anterior horn cells or their axons. A cervical magnetic resonance image revealed a large intramedullary mass extending from the inferior aspect of the fourth ventricle down to the level of T2. A biopsy of the lesion was consistent with a low-grade astrocytoma.

Muscle computed tomography in adult-onset acid maltase deficiency

Nine patients with adult-onset acid maltase deficiency (Pompe's disease) were examined clinically and with computed tomography (CT). The CT scan showed early and severe involvement of the muscles of trunk and thighs, with selective sparing of the tensor fasciae latae, short head of biceps femoris, gracilis, and sartorius muscles. Shoulder and leg muscles were less affected. The disease spread over the years from trunk to extremities. Muscle strength and CT findings were positively correlated.

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.