Isolated mitochondrial myopathy associated with muscle coenzyme Q10 deficiency

Background: Primary coenzyme Q(10) (CoQ(10)) deficiency is rare. The encephalomyopathic form, described in few families, is characterized by exercise intolerance, recurrent myoglobinuria, developmental delay, ataxia, and seizures. Objective: To report a rare manifestation of CoQ10 deficiency with isolated mitochondrial myopathy without central nervous system involvement. Methods: The patient was evaluated for progressive muscle weakness. Comprehensive clinical evaluation and muscle biopsy were performed for histopathologic analysis and mitochondrial DNA and respiratory chain enzyme studies. The patient began taking 150 mg/d of a CoQ(10) supplement, Results: The elevated creatine kinase and lactate levels with abnormal urine organic acid and acylcarnitine profiles in this patient suggested a mitochondrial disorder. Skeletal muscle histochemical evaluation revealed ragged red fibers, and respiratory chain enzyme analyses showed partial reductions in complex I, I + III, and II + III activities with greater than 200% of normal citrate synthase activity. The CoQ(10) concentration in skeletal muscle was 46% of the normal reference mean. The in vitro addition of 50 mumol/L of coenzyme Q(1) to the succinate cytochrome-c reductase assay of the patient's skeletal muscle whole homogenate increased the succinate cytochrome-c reductase activity 8-fold compared with 2.8-fold in the normal control homogenates. Follow-up of the patient in 6 months demonstrated significant clinical improvement with normalization of creatine kinase and lactate levels. Conclusions: The absence of central nervous system involvement and recurrent myoglobinuria expands the clinical phenotype of this treatable mitochondrial disorder. The complete recovery of myopathy with exogenous CoQ(10) supplementation observed in this patient highlights the importance of early identification and treatment of this genetic disorder.