Muscle carnitine deficiency. Genetic heterogeneity.
Two types of lipid storage myopathy have been associated with decreased content of carnitine in muscle. In "muscle carnitine deficiency", carnitine concentration is normal in serum, but reduced in muscle. In "systemic carnitine deficiency", apparently due to imparied synthesis of carnitine in the liver, carnitine content is low in both serum and muscle. We studied a woman with a corticosteroid-responsive, probably autosomal recessive, lipid storage myopathy. Carnitine therapy was ineffective and carnitine failed to correct the impaired fatty acid oxidation in muscle homogenates, in contrast to a previous case. Carnitine transport into skeletal muscle was normal. These observations suggest that ll cases of "muscle carnitine deficiency are not the same.