Lipid storage myopathy associated with sertraline treatment is an acquired mitochondrial disorder with respiratory chain deficiency

Lipid storage myopathies are considered inborn errors of metabolism affecting the fatty acid metabolism and leading to accumulation of lipid droplets in the cytoplasm of muscle fibers. Specific diagnosis is based on investigation of organic aids in urine, acylcarnitines in blood and genetic testing. An acquired lipid storage myopathy in patients treated with the antidepressant drug sertraline, a serotonin reuptake inhibitor, has recently emerged as a new tentative differential diagnosis. We analyzed the muscle biopsy tissue in a group of 11 adult patients with muscle weakness and lipid storage myopathy which developed at a time when they were on sertraline treatment. This group comprise most patients with lipid storage myopathies in western Sweden during the recent nine-year period. By enzyme histochemistry, electron microscopy, quantitative proteomics, immunofluorescence of the respiratory chain subunits, western blot and genetic analyses we demonstrate that muscle tissue in this group of patients exhibit a characteristic morphological and proteomic profile. The patients also showed an acylcarnitine profile in blood suggestive of multiple acyl-coenzyme A dehydrogenase deficiency, but no genetic explanation was found by whole genome or exome sequencing. By proteomic analysis the muscle tissue revealed a profound loss of Complex I subunits from the respiratory chain and to some extent also deficiency of Complex II and IV. Most other components of the respiratory chain as well as the fatty acid oxidation and citric acid cycle were upregulated in accordance with the massive mitochondrial proliferation. The respiratory chain deficiency was verified by immunofluorescence analysis, western blot analysis and enzyme histochemistry. The typical ultrastructural changes of the mitochondria included pleomorphism, dark matrix and frequent round osmiophilic inclusions. Our results show that lipid storage myopathy associated with sertraline treatment is a mitochondrial disorder with respiratory chain deficiency and is an important differential diagnosis with characteristic features.