Laboratory Features in Objective-C

Printer Data Matrix 2d barcode in Objective-C Laboratory Features

Depending on the subtype of GSD IV, de ciency of branching enzyme may be demonstrated in muscle, peripheral nerve, broblasts, or leukocytes70,71,73,76,82,83 In patients with primary neuromuscular involvement, the de ciency may be noted only in muscle70 Branching enzyme activity can be normal in the muscle in patients with adult polyglucosan body neuropathy71,73 The serum CK may be normal or slightly elevated EMG reveals myopathic features and muscle membrane instability similar to that observed with GSDs II and III In patients with polyglucosan body neuropathy, an axonal sensorimotor neuropathy is apparent while the EMG abnormalities re ect a superimposed polyradiculopathy EKG can demonstrate progressive conduction defects leading to complete atrio-ventricular (A-V) block78 Echocardiogram may reveal a dilated cardiomyopathy78

muscle4,70,73,74,77 79 These polyglucosan bodies are PAS positive and diastase resistant, suggesting the accumulation of polysaccharides other than glycogen (Fig 26 3) This polysaccharide resembles amylopectin in that it has longer than normal peripheral chains and few branch points58 Autopsy studies have demonstrated abnormal polysaccharide material in the liver, heart, skeletal muscle, and in neurons of the brain and the spinal cord The abnormal polysaccharide material is more abundant in the motor neurons than in other nerve cells and affects all motor neurons of the brainstem and spinal cord84

The disease is inherited in an autosomal-recessive manner Deletions, nonsense, and missense mutations within the GBE1 (glycogen branching enzyme) gene at chromosome 3p12 have been identi ed in the severe hepatic, benign hepatic, and the neuromuscular forms of GSD IV, including adult polyglucosan body disease68,72,82,83 There are phenotypic variability and differential expression of branching enzyme activity The mechanism by which the abnormal accumulation of polysaccharide results in muscle damage is not known

Liver transplantation has been performed in some children with GSD IV with bene cial results85 87 Apparently, systemic microchimerism occurs after liver allotransplantation and can ameliorate pancellular enzyme de ciencies in this disease Most of the patients became free of liver, neuromuscular, and cardiac dysfunction, with reduced polysaccharide accumulation in these

Routine light and electron microscopy reveals deposition of varying amounts of nely granular and lamentous polysaccharide (polyglucosan bodies) in the central nervous system (CNS), peripheral nerves (axons and Schwann cells), skin, liver, and cardiac and skeletal

tissues on long-term follow-up (mean 42 months) However, at least one child died from cardiomyopathy due to massive deposition of polysaccharide in the heart 21/2 years after transplantation85 No other medical therapies have been demonstrated to be effective

Muscle biopsies demonstrate variability in ber size, scattered necrotic and regenerating bers, and excessive accumulation of glycogen in the subsarcolemmal and intermyo brillar areas (see 3, Figure 3 6)4,95,96 Staining for myophosphorylase is absent, and biochemical assay for myophosphorylase reveals absent or signi cantly reduced activity

The type V glycogenosis (myophosphorylase de ciency), more commonly known as McArdle disease, is the most common disorder of carbohydrate metabolism McArdle disease is an autosomal-recessive disorder that usually presents with exercise intolerance in childhood or young adults (Table 26 1, Fig 26 1)3,6,58,88 Patients complain of exertional muscle pain and cramps induced by brief, but very intense, activities (eg, weight lifting and sprinting), but these can also occur following prolonged low-intensity exercises (eg, swimming and jogging) If individuals who are affected ignore these symptoms and continue to exercise at a high level, the muscle pain and cramping can become quite intense and electrically silent contractures may develop Some patients present with fatigue following exercise without associated cramps or muscle pain Many patients note a second wind phenomenon in which, after the onset of mild exertional myalgias or cramps (usually after 10 minutes of exercise), the muscle pain and sense of intolerance may dissipate and the individual may continue with the exercise at the previous or a slightly reduced level89 The second wind phenomenon is the result of mobilization and use of blood-borne glucose Overt myoglobinuria usually does not occur until the second or third decade, although it has developed as early as 8 years of age90 Approximately 50% of attacks of myoglobinuria are exertionally related and one-third of cases are complicated by renal insuf ciency Most patients have normal motor examinations between attacks of muscle cramping However, xed proximal weakness develops in as many as one-third of patients perhaps as a result of recurrent bouts of rhabdomyolysis Rare patients present with progressive proximal muscle atrophy and weakness in late-adult life rather than exercise intolerance91 Weakness may involve the arms more than the legs and can be asymmetric Finally, a few cases have been reported with congenital weakness, some of which were rapidly progressive, leading to ventilatory failure within the rst year of life92,93