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Exercise Capacity and Biochemical Profile during Exercise in Patients with Glycogen Storage Disease Type I

Charles Dent Metabolic Unit, National Hospital for Neurology and Neurosurgery (H.R.M., A.C., P.J.L.), London WC1N 3BG, United Kingdom; Department of Cardiology, Royal Brompton Hospital (P.G., L.C.D.), London, SW3 6NP United Kingdom; and Department of Biochemistry and Metabolism, Institute of Child Health (J.V.L.), London WC1N 1EM, United Kingdom

Address all correspondence and requests for reprints to: Dr. Helen Mundy, Charles Dent Metabolic Unit, National Hospital for Neurology and Neurosurgery, Queen Square, London WC1N 3BG, United Kingdom. E-mail: ceri{at}davies151.freeserve.co.uk.

Glycogen storage disease type I (GSD-I) is an inherited disorder of carbohydrate metabolism. Hepatic glucose-6-phosphatase is deficient, leading to impaired gluconeogenesis and glycogenolysis. Patients prevent fasting hypoglycemia by frequent feeds of low glycemic index foods. Normal muscle does not contain glucose-6-phosphatase, and GSD-I is usually classified as a hepatic glycogenosis. However, clinical experience has suggested that patients have decreased cardiovascular fitness, but this had not been formally investigated. This paper reports the results of maximal treadmill cardiopulmonary exercise testing in adult patients with GSD-I. It documents a major reduction in exercise capacity in these patients and demonstrates biochemical aspects of exercise that are different from those of normal controls. All patients showed a reduction in exercise capacity, but there was a wide range of exercise tolerance. Additional work needs to address whether improved adherence to or intensification of therapy in adulthood will ameliorate exercise intolerance.