OBJECTIVE: It is unclear to what extent muscle phosphorylase b kinase (PHK) deficiency is associated with exercise-related symptoms and impaired muscle metabolism, because 1) only four patients have been characterized at the molecular level, 2) reported symptoms have been nonspecific, and 3) lactate responses to ischemic handgrip exercise have been normal. METHODS: We studied a 50-year-old man with X-linked PHK deficiency using ischemic forearm and cycle ergometry exercise tests to define the derangement of muscle metabolism. We compared our findings with those in patients with McArdle disease and in healthy subjects. RESULTS: Sequencing of PHKA1 showed a novel pathogenic mutation (c.831G>A) in exon 7. There was a normal increase of plasma lactate during forearm ischemic exercise, but lactate did not change during dynamic, submaximal exercise in contrast to the fourfold increase in healthy subjects. Constant workload elicited a second wind in all patients with McArdle disease, but not in the patient with PHK deficiency. IV glucose administration appeared to improve exercise tolerance in the patient with PHK deficiency, but not to the same extent as in the patients with McArdle disease. Lipolysis was higher in the patient with PHK deficiency than in controls. CONCLUSION: These findings demonstrate that X-linked PHK deficiency causes a mild metabolic myopathy with blunted muscle glycogen breakdown and impaired lactate production during dynamic exercise, which impairs oxidative capacity only marginally. The different response of lactate to submaximal and maximal exercise is likely related to differential activation mechanisms for myophosphorylase.

McArdle's disease is a common disorder of muscle metabolism and is due to myophosphorylase deficiency. The major complaint of patients with this disease is effort intolerance. Although the clinical features of affected patients are well known, their daily lifestyle is not well documented. The main objective of this work was to assess their mean daily energy expenditure (DEE) and compare it with control subjects. Thirty patients and 87 control subjects completed a questionnaire. A 3-day self-record of daily physical activities was used to estimate the mean DEE for patients and control subjects. A separate section of the questionnaire was used to assess patients' clinical features and daily lifestyle. The DEE of patients (44.1 +/- 6.9 kcal/kg) was not significantly different from control subjects (44.5 +/- 5.6 kcal/kg). Half of the patients with McArdle's disease performed a daily physical leisure activity as sport, sometimes at a high level (17%). Despite large individual variation, physical abilities and patients' symptoms were negatively correlated. Physical leisure activity significantly decreased the sensation of muscle pain (P < 0.03). These findings show that patients with McArdle's disease do not have a strictly sedentary lifestyle. Moreover, physical exercise appears to have positive effects on the main clinical features, such as effort intolerance. Thus, regular, moderate physical activity may be beneficial in McArdle's disease.

McArdle's disease in childhood: report of a new case. Eur J Paediatr Neurol. 1998;2(5):269-73.

McArdle's disease (glycogenosis type V) is an inherited glycogen storage disease characterized clinically by myalgia, cramps and sometimes myoglobinuria, triggered by exercise. The onset of exercise intolerance is usually in late childhood or adolescence and diagnosis is exceptionally established during infancy. We report the case of a 6-year-old girl who had been complaining of aching muscles for a long time, and who presented after a near-drowning incident, with extensive muscle necrosis, probably secondary to myophosphorylase deficiency-induced cramps. These unusual manifestations led to the diagnosis of this rare disorder. We compare the clinical findings of this case to nine previous reports. This highlights the heterogeneous spectrum of this disease in childhood and supports the distinction of three clinical pictures in childhood: a neonatal form rapidly fatal, a milder form with congenital myopathic symptoms and a benign classical form with myalgia, cramps and pigmenturia.

INTRODUCTION: Pompe's disease, also called glycogen storage disease type II or acid maltase deficiency, is an autosomal recessive disease caused by an enzymatic deficiency of acid-alpha-glucosidase (GAA). This deficiency causes an accumulation of intralysosomal glycogen in different organs. The classic form appears in the newborn with a very severe hypotonia and cardiomyopathy, which lead to death before age two. Less frequently, the disease appears only in childhood or in adult life, so called late-onset Pompe's disease. This form causes a very progressive limb-girdle myopathy and restrictive respiratory failure. The diagnosis is based on a low level of GAA either in the muscle biopsy or in the leucocytes. We report six cases of late-onset Pompe's disease from the Languedoc-Roussillon district. METHOD: Our work was a retrospective analysis of all cases of Pompe disease diagnosed in adults between 1975 and 2006 at the Montpellier and Nîmes University Hospital. We describe the clinical presentation and course of this form and explain the diagnostic approach. Results. The mean age at onset was 44.3 years (range: 36-60 years). The first symptom was fatigability (50%), gait difficulty (50%) and dyspnea (16%). The mean delay from symptom onset to diagnosis was 8.4 years (range: 17 years). Fatal outcome due to respiratory failure was noted in three patients. The mean time between symptom onset and death (four patients) was 20.75 years (range: 37 years). The diagnosis was made on the muscle biopsy showing a low level of GAA. Muscle was strictly normal on the morphologic study in one patient, pointing out the requirement for enzymatic analysis. Molecular confirmation was available in one patient. DISCUSSION: Late-onset Pompe's disease is a possible cause of limb-girdle myopathy. Respiratory involvement is a characteristic feature. Enzymatic assay of GAA activity on the muscle biopsy is required for certain diagnosis. CONCLUSION: It is very important to recognize the adult form of Pompe's disease, a possible cause of limb-girdle myopathy, in order to search for respiratory failure and propose non-invasive ventilation if necessary. Moreover, substitutive therapy (recombinant acid-alpha-glucosidase) has shown efficiency for the classical infantile form of Pompe's disease and such treatment could be proposed for the adult form if larger studies confirm its efficacy.

Pompe disease (glycogen storage disease type II): clinical features and enzyme replacement therapy.Acta Neurol Belg. 2006 Jun;106(2):82-6.

Pompe disease (glycogen storage disease type II, acid maltase deficiency) is a progressive metabolic myopathy caused by deficiency of the lysosomal enzyme acid alpha-glucosidase. This leads to an accumulation of glycogen in various tissues of the body, most notably in skeletal muscle. The disease has an autosomal recessive inheritance with a predicted frequency of 1 :40.000. Pompe disease is a continuous spectrum but for clinical practice different subtypes are recognized. The classic infantile form of the disease occurs in infants (shortly after birth) and is characterized by generalized hypotonia, failure to thrive, and cardiorespiratory failure. Patients usually die within the first year of life. The non-classic or late-onset form of the disease may occur at any age in childhood or adulthood. It presents predominantly as a slowly progressive proximal myopathy, with or without respiratory failure. Enzyme replacement therapy (ERT) is under study as treatment for the disease. The first results with recombinant human alpha-glucosidase are promising and a registered therapy seems near. Beneficial effects of ERT have been reported both in patients with the classic infantile form as well as in patients with the non-classic or late-onset form of the disease. The best therapeutic results are achieved when ERT is started early in the course of symptom development and before irreversible muscular damage has occurred. Detailed knowledge about the natural course of the disease becomes more and more essential to determine the indication and timing of treatment.

Acid alpha-glucosidase deficiency (Pompe disease).Curr Neurol Neurosci Rep. 2007 Jan;7(1):71-7.

The development and recent approval of recombinant acid alpha-glucosidase for enzyme replacement therapy have been major milestones in Pompe disease research. Acid alpha-glucosidase is the enzyme responsible for degradation of glycogen polymers to glucose in the acidic milieu of the lysosomes. Cardiac and skeletal muscles are the two major tissues affected by the accumulation of glycogen within the lysosomes. Both cardiomyopathy and skeletal muscle myopathy are observed in patients with complete enzyme deficiency; this form of the disease is fatal within the first year of life. Skeletal muscle myopathy eventually leading to respiratory insufficiency is the predominant manifestation of partial enzyme deficiency. The recombinant enzyme alglucosidase alfa is the first drug ever approved for this devastating disorder. This review discusses the benefits and the shortcomings of the new therapy.