A Skeletal-Muscle Disorder Associated with Intermittent Symptoms and a Possible Defect of Lipid Metabolism

Abstract

Identical-twin 18-year-old girls have had since early childhood intermittent symptoms of aching muscle "cramps," without weakness, usually mild but occasionally severe, with myoglobinuria. Symptoms have not limited exercise but sometimes were induced by exercise several hours earlier. Defective availability of an energy source to muscle was suspected, but carbohydrate utilization was apparently normal. Identical episodes were precipitated, without increased exercise, by fasting for 24 to 72 hours or an isocaloric high-fat low-carbohydrate diet, and were accompanied by the following: cramping muscle aches without weakness; nausea and malaise; marked rise of serum GOT, GPT, CPK, aldolase and LDH; no ketonemia or ketonuria (abnormal response); unchanged blood glucose, electrolytes, lactate and pyruvate; and normal electrocardiograms. Refeeding with a normal diet corrected the abnormalities. Oral medium-chain triglycerides produced prompt ketonemia and ketonuria (normal response). Free fatty acid mobilization during fasting was normal. A defect of long-chain fatty acid utilization was considered a possible explanation.