A case of mitochondrial encephalomyopathy associated with a muscle coenzyme Q10 deficiency

We report severe coenzyme Q(10) deficiency of muscle in a 4-year-old boy presenting with progressive muscle weakness, seizures, cerebellar syndrome, and a raised cerebro-spinal fluid lactate concentration. State-3 respiratory rates of muscle mitochondria with glutamate, pyruvate, palmitoylcarnitine, and succinate as respiratory substrates were markedly reduced, whereas ascorbate/N,N,N',N'tetramethyl-p-phenylenediamine were oxidized normally. The activities of complexes I, II, LII and IV of the electron transport chain were normal, but the activities of complexes I+III and II+III, both systems requiring coenzyme Q(10) as an electron carrier, were dramatically decreased. These results suggested a defect in the mitochondrial coenzyme Q(10) content. This was confirmed by the direct assessment of coenzyme Q(10) level by high-performance liquid chromatography in patient's muscle homogenate and isolated mitochondria, revealing levels of 16% and 6% of the control values, respectively. We did not find any impairment of the respiratory chain either in a lymphoblastoid cell line or in skin cultured fibroblasts from the patient, suggesting that the coenzyme Q(10) depletion was tissue-specific. This is a new case of a muscle deficiency of mitochondrial coenzyme Q in a patient suffering from an encephalomyopathy. (C) 1998 Elsevier Science B.V.