Biochemical study on lipid metabolism in lipid storage myopathy

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We studied lipid metabolism in clutured fibroblasts from a patient with lipid storage myopathy. The patient has slowly progressive myopathy, pigmentary retinal degeneration, neurosensory hearing loss. There were many vacuoles containing neutral lipid in skeletal muscle fibers, leukocytes, and cultured fibroblasts.Carnitine content and the activities of carnitine palmitoyltransferase and mitochondrial electron transport system were normal, and the ratio of acylcarnitine to free carnitine was elevated in skeletal muscle. The level of triglyceride content of the cultured fibroblasts was ten times higher than that of controls, and fatty acid composition was normal. The oxidation of long-chain fatty acid was impaired (37% of control values), while the oxidation reaction of medium-chain and short-chain fatty acid were normal in the cultured fibroblasts. The activities of enzymes working on long-chain fatty acid oxidation were normal. When the fibroblasts were fed with radiolabeled oleate for 6 hrs, the triglyceride synthsis was increased twice as controls. Pulse-chase experiment showed the reduced degradation of synthesized triglyceride. The activities of acidic, neutral, and alkaline lipase were normal level in fibroblasts extracts.The regulation in both long-chain fatty acid oxidation and triglyceride degradation may be impaired, which causes the intracellure accumulation.