A MYOPATHY PRESENTING IN ADULT LIFE WITH FEATURES SUGGESTIVE OF GLYCOGEN STORAGE DISEASE

Phenotypic implications of pathogenic variant types in Pompe disease

Newborn screening and therapies for Pompe disease (glycogen storage disease type II, acid maltase deficiency) will continue to expand in the future. It is thus important to determine whether enzyme activity or type of pathogenic genetic variant in GAA can best predict phenotypic severity, particularly the presence of infantile-onset Pompe disease (IOPD) versus late-onset Pompe disease (LOPD). We performed a retrospective analysis of 23 participants with genetically-confirmed cases of Pompe disease. The following data were collected: clinical details including presence or absence of cardiomyopathy, enzyme activity levels, and features of GAA variants including exon versus intron location and splice site versus non-splice site. Several combinations of GAA variant types for individual participants had significant associations with disease subtype, cardiomyopathy, age at diagnosis, gross motor function scale (GMFS), and stability of body weight. The presence of at least one splice site variant (c.546 G > C/p.T182 = , c.1076-22 T > G, c.2646 + 2 T > A, and the classic c.-32-13T > G variant) was associated with LOPD, while the presence of non-splice site variants on both alleles was associated with IOPD. Enzyme activity levels in isolation were not sufficient to predict disease subtype or other major clinical features. To extend the findings of prior studies, we found that multiple types of splice site variants beyond the classic c.-32-13T > G variant are often associated with a milder phenotype. Enzyme activity levels continue to have utility for supporting the diagnosis when the genetic variants are ambiguous. It is important for newly diagnosed patients with Pompe disease to have complete genetic, cardiac, and neurological evaluations.

Inborn errors of metabolism and expanded newborn screening: review and update

Inborn errors of metabolism (IEM) are a phenotypically and genetically heterogeneous group of disorders caused by a defect in a metabolic pathway, leading to malfunctioning metabolism and/or the accumulation of toxic intermediate metabolites. To date, more than 1000 different IEM have been identified. While individually rare, the cumulative incidence has been shown to be upwards of 1 in 800. Clinical presentations are protean, complicating diagnostic pathways. IEM are present in all ethnic groups and across every age. Some IEM are amenable to treatment, with promising outcomes. However, high clinical suspicion alone is not sufficient to reduce morbidities and mortalities. In the last decade, due to the advent of tandem mass spectrometry, expanded newborn screening (NBS) has become a mandatory public health strategy in most developed and developing countries. The technology allows inexpensive simultaneous detection of more than 30 different metabolic disorders in one single blood spot specimen at a cost of about USD 10 per baby, with commendable analytical accuracy and precision. The sensitivity and specificity of this method can be up to 99% and 99.995%, respectively, for most amino acid disorders, organic acidemias, and fatty acid oxidation defects. Cost-effectiveness studies have confirmed that the savings achieved through the use of expanded NBS programs are significantly greater than the costs of implementation. The adverse effects of false positive results are negligible in view of the economic health benefits generated by expanded NBS and these could be minimized through increased education, better communication, and improved technologies. Local screening agencies should be given the autonomy to develop their screening programs in order to keep pace with international advancements. The development of biochemical genetics is closely linked with expanded NBS. With ongoing advancements in nanotechnology and molecular genomics, the field of biochemical genetics is still expanding rapidly. The potential of tandem mass spectrometry is extending to cover more disorders. Indeed, the use of genetic markers in T-cell receptor excision circles for severe combined immunodeficiency is one promising example. NBS represents the highest volume of genetic testing. It is more than a test and it warrants systematic healthcare service delivery across the pre-analytical, analytical, and post-analytical phases. There should be a comprehensive reporting system entailing genetic counselling as well as short-term and long-term follow-up. It is essential to integrate existing clinical IEM services with the expanded NBS program to enable close communication between the laboratory, clinicians, and allied health parties. In this review, we will discuss the history of IEM, its clinical presentations in children and adult patients, and its incidence among different ethnicities; the history and recent expansion of NBS, its cost-effectiveness, associated pros and cons, and the ethical issues that can arise; the analytical aspects of tandem mass spectrometry and post-analytical perspectives regarding result interpretation.

Dementia of frontal lobe type due to adult polyglucosan body disease

We describe a patient with adult polyglucosan body disease (APBD) who presented with a dementia of frontal lobe type (FLD), with a neurogenic bladder but no symptoms of sensory motor peripheral neuropathy. Diagnosis was made from a cerebral biopsy specimen which showed an accumulation of intra-axonal polyglucosan bodies in the central nervous system. This case differs from the usual presentation, in which gait disturbance is the main symptom and diagnosis is possible by sural nerve biopsy. Little is known about the neuropsychological pattern of APBD dementia but FLD has not previously been described. APBD is a heterogeneous clinical entity of unknown cause. This diagnosis must be considered in elderly patients with dementia.

Juvenile hereditary polyglucosan body disease with complete branching enzyme deficiency (type IV glycogenosis)

Polyglucosan body diseases in adults, contrary to infantile cases (Andersen's disease or type IV glycogenosis or amylopectinosis), are usually not associated with a significant deficiency of the branching enzyme (= amylo-1,4-1,6 transglucosidase). We, therefore, report on a 19-year-old male with complete branching enzyme deficiency presenting with severe myopathy, dilative cardiomyopathy, heart failure, dysmorphic features, and subclinical neuropathy. His 14-year-old brother had similar symptoms and was erroneously classified by a previous muscle biopsy as having central core disease but could later be identified as also having polyglucosan body myopathy. The skeletal muscle, endomyocardiac, and sural nerve biopsies as well as the autopsy revealed extraordinarily severe deposits of polyglucosan bodies not only in striated and smooth muscle fibers, but also in histiocytes, fibroblasts, perineurial cells, axons and astrocytes. Occasional paracrystalline mitochondrial inclusions were also noted. Thus, this patient represents to our knowledge the first juvenile, familial case of polyglucosan body disease with total branching enzyme deficiency and extensive polyglucosan body storage.

Polysaccharide storage myopathy associated with recurrent exertional rhabdomyolysis in horses

A polysaccharide storage myopathy is described in nine Quarterhorses, Quarterhorse crossbreds, American Paints and Appaloosa horses which had a history of recurrent exertional rhabdomyolysis. Muscle biopsies were characterized by high muscle glycogen concentrations with up to 5% of type 2 muscle fibers containing inclusions which stained positively with the periodic acid Schiff (PAS) stain. The inclusions were classified as an acid mucopolysaccharide, based on their histochemical staining characteristics. Ultrastructural studies revealed that the inclusions were composed of beta glycogen particles interspersed among arrays of filamentous material. In addition, many type 2 fibers contained multiple subsarcolemmal vacuoles. These vacuoles stained lightly with eosin and did not stain positively with PAS. Centrofascicular atrophy and necrosis of scattered type 2 fibers were present in biopsies from some horses. No glyco(geno)lytic enzyme deficiencies were identified using a biochemical screening test for anaerobic glycolysis. Attempts to measure branching enzyme activities in both affected and control samples were unsuccessful, employing methods developed for human muscle. The polysaccharide accumulation in these horses may represent a hereto yet undefined metabolic disorder of skeletal muscle.

Polyglucosan body myopathy: a new case

We report a 51-yr-old woman with late-onset progressive weakness affecting proximal limb muscles. Muscle biopsy revealed a vacuolar myopathy with accumulation of amylopectin-like polysaccharide resembling the polyglucosan found in type IV glycogenosis and adult-onset polyglucosan body disease. A biochemical study ruled out specific enzymatic defects known to cause storage of this abnormal material. Our case confirms the existence of a 'polyglucosan body myopathy' as a distinct clinicopathological entity in which the biochemical defect is unknown.

Primary lipid cardiomyopathy

In this communication, we describe an isolated, apparently congenital cardiomyopathy (CMP) characterized by the accumulation of stainable lipid in mitochondria of cardiomyocytes. This lesion, which we term primary lipid cardiomyopathy, has not been reported so far. The structural alteration was associated with progressive heart failure, leading to death at the age of 3 years, and with massive hypertrophy of myocardium. Lipid storage in heart muscle cells resulted in an impressive yellow to orange color of the myocardium. We suggest that this type of primary CMP may represent a new member within the group of mitochondrial CMPs. Possible pathogenic mechanisms are discussed.

Polysaccharide storage myopathy

In a woman with a slowly progressive adult onset proximal myopathy, muscle biopsy showed storage of PAS positive material in type 1 fibers. This material consisted of a branched chain polysaccharide associated with a mucoprotein. No abnormality of glycogen-pathway enzymes was detected. This suggested that this polysaccharide accumulation occurred because the polysaccharide was laid down in a non-bioavailable form. The clinical and histochemical features in this patient and in the few similar reported cases indicate that polysaccharide storage myopathy is a distinct entity that is allied to the glycogen storage myopathies.

A new variant of type IV glycogenosis: deficiency of branching enzyme activity without apparent progressive liver disease

Type IV glycogenosis is due to branching enzyme deficiency and is usually manifested clinically by progressive liver disease with cirrhosis and hepatic failure between the second and fourth years of life. We describe a 5-year-old boy who, following an acute febrile illness at 2 years of age, was first noted to have hepatomegaly with mildly elevated serum transaminase levels. Liver biopsy revealed hepatic fibrosis with periodic-acid Schiff-positive, diastase-resistant inclusions in hepatocytes and fibrillar inclusions characteristic of amylopectin by electron microscopy. Enzymatic assay revealed deficient hepatic branching enzyme activity with normal activity of glucose-6-phosphatase, debranching enzyme and phosphorylase activities. During the succeeding 3 years, he grew and developed normally with apparent resolution of any clinical evidence of liver disease and only intermittent elevation in serum transaminase levels associated with fever and prolonged fasting. Repeat liver biopsy at 4 years of age showed persistence of scattered hepatocellular periodic-acid Schiff-positive, diastase-resistant inclusions, but no progression of hepatic fibrosis in spite of persistent deficiency of hepatic branching enzyme activity. Skeletal muscle and skin fibroblasts from the patient also showed deficient enzyme activity. Skin fibroblasts from both parents exhibited half the normal control activity, suggesting a heterozygote state. This is the first documented patient with deficiency of branching enzyme but without evidence of progressive hepatic disease. This patient, coupled with reports of other patients with late onset hepatic or muscle disease with branching enzyme deficiency, suggests that the defect resulting in Type IV glycogen storage disease is more heterogenous and possibly more common than previously suspected.

Intra-axonal polysaccharide deposits in the peripheral nerve seen in adult polysaccharide storage myopathy

This is the first report of an adult polysaccharide storage myopathy demonstrating polysaccharide deposits within the axons of the peripheral nerve. Histochemical and electron-microscopic studies revealed that the intra-axonal deposits were basophilic, PAS-positive, diastase-resistant, and composed of filamentous and granular material. The structural similarity among the polysaccharide deposits in our case, amylopectin-like materials in type IV glycogenosis, Lafora bodies, corpora amylacea, and polyglucosan bodies is discussed.

Inherited metabolic myopathy with storage of glycoproteins and glycosaminoglycans

Two related patients (mother and daughter, ages 28 and 5 years) showed mild to moderate weakness and atrophy of facial and shoulder muscles with congenital onset and minimal progression. Serum creatine kinase was elevated in the child. Muscle biopsy showed normal light-microscopic and histochemical findings, but scattered sarcoplasmic vacuoles with storage of granular material were evident on electron microscopy. Storage of granular material was also identified in fibroblasts which were weakly PAS-positive, stained metachromatically with toluidine blue and orthochromatically with alcian blue. Muscle glycogen values were low-normal. Repeated biochemical studies of cultured fibroblasts identified excessive storage of glycosaminoglycans and glycoproteins. The uptake of 3H-glucosamine in cultured fibroblasts was 1.7-3.4 times greater in the patients than in control individuals, while the rate of turnover of the radioisotope was normal. These findings suggest that the genetic defect in this inherited metabolic myopathy is related to excessive synthesis of glycosaminoglycans and glycoproteins.

An adult case of Andersen's disease--Type IV glycogenosis. A clinical, histochemical, ultrastructural and biochemical study

A middle-aged man presented with a thirty-year history of progressive, asymmetrical limb-girdle weakness. The muscle biopsy revealed a vacuolar myopathy. The vacuoles which did not disrupt the fibre outline, lay in a subsarcolemmal position. They were PAS-positive and the material was partially resistant to diastase digestion. Electron microscopy showed the vacuoles to contain free unbound glycogen with filamentous material. Leucocyte brancher enzyme activity was normal but the muscle activity was less than half the control value. Histochemical and ultrastructural characteristics of the storage material resemble the amylopectin polysaccharide deposits seen in childhood Type IV glycogenosis.

Polysaccharide (amylopectin-like) storage myopathy histochemical ultrastructural and biochemical studies

A case of an adult polysaccharide myopathy is reported in a patient with progressive muscular atrophy and weakness of limb girdles. Histochemistry and electron microscopy showed in some muscle fibers, a storage material composed of amylopectin-like filaments. Biochemical results were normal and no enzyme deficiency was found. This case is compared with three other published cases. Pathological conditions with amylopectin or amylopectin-like storage material are reviewed.

A congenital myopathy of unknown origin

Parallel with the clinical and histochemical investigations, an ultrastructural examination of a muscle biopsy specimen was made, in order to detect any slight cellular alterations which cannot possibly be discovered through any other methods, and to identify a muscle disease of unknown origin.