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Glycogen storage disease due to amylo-1,6-glucosidase deficiency was diagnosed in a 21-year-old patient. The enzyme defect was demonstrated by biochemical analysis of muscle tissue, the glycogen content of which was typically increased. Investigation of the patient's kindred showed that his 25-year-old sister was also affected. This report sets out to show that in adolescence and in adult life myopathy may be the leading symptom of the disease. Besides the clinical symptoms of muscle weakness and stiffness, an increase in serum creatine kinase usually is found. While an increase in the glycogen content of skeletal muscle has been known since the first description of this glycogen storage disease, it was believed that the glycogen deposits do not cause a clinically relevant disturbance of muscle function. A review of the literature and our own observations show that this assumption has to be at least partially revised. In patients with unclear myopathy who had hepatomegaly during childhood the possibility of glycogenosis due to amylo-1,6-glucosidase deficiency should be considered, especially if symptoms of hypoglycemia are reported. In the patient as well as in his sister marked kyphoscoliosis was present. Whether there is a connection between skeletal deformity and enzyme defect cannot be determined as the patients were available for further studies.

Metabolic myopathies are a rare group of disorders. These myopathies reveal a varying severity of a proximal, distal or generalized muscular involvement indicating a progressive myopathy or recurrent episodes of weakness, pain, cramps and stiffness combined with exercise. Some important disorders and their biochemical defects are described. Particular attention is paid to helpful biochemical investigative methods.

A new type of hereditary muscle disease, characterized by weakness and painful spasms during effort, without electrical activity in the shortened muscles, is described. These phenomena are limited principally to the upper limbs. In addition we found electromyographical signs of a generalized myotonic syndrome. The histological and histochemical investigations reveal only minimal non-specific signs of myopathy. The activities of CPK and aldolase in the blood serum are increased at times. A normal elevation of venous lactate was observed during ischemic work. The biochemical studies of muscular tissue exhibit normal activities of the analyzed enzymes, especially as regards phosphorylase. An increased concentration of calcium ions in blood serum may be related to the contraction during strenuous work; it is known that calcium ions are an important factor in the contraction-relaxation cycle of striated muscle. The age of manifestation varied from 4 to 33 years in 4 cases of the relatives observed. The disease shows no signs of aggravation as to the severity and extent of the disorders. The nature of the underlying metabolic defect is still unknown.