Normal insulin receptors in mitochondrial myopathies with ophthalmoplegia

Seven patients with histologically proven mitochondrial myopathy with ophthalmoplegia (OMM), 6 of them nondiabetic, 1 affected by diabetes mellitus (DM), were submitted to a study of glucose tolerance and of insulin receptors on peripheral mononuclear cells and cultured skin fibroblasts. The diabetic patient, who had the typical features of the Kearns-Sayre syndrome (KSS) and deleted muscle mitochondrial DNA (mtDNA) presented a low insulin secretion rate under physiological stimuli (intravenous glucose and glucagon) whereas the insulin receptor parameters were found normal. The other patients showed a normal glucose tolerance and normal insulin receptors. Our data support the hypothesis that insulin receptors are not involved in the pathogenesis of DM associated with mitochondrial encephalomyopathies, in contrast to other neuromuscular inherited disorders. The clinical and biological features of DM presented by our KSS patient show normal insulin receptor parameters in spite of a defective insulin secretion, possibly depending on mitochondrial dysfunction.