Recurrent myoglobinuria and deranged acylcarnitines due to a mutation in the mtDNA MT-CO2 gene

Mitochondrial myopathies commonly present with exercise intolerance typified by breathlessness and fatigue on exercise. In contrast, exercise-induced rhabdomyolysis and myoglobinuria occur rarely. We present a 43-year-old man with a lifelong history of exercise intolerance associated with myalgia and recurrent episodes of exercise-induced myoglobinuria. From early childhood, he had weekly episodes of myoglobinuria, which became infrequent (every 3 months) as an adult. Carnitine transporter defect was suspected, because carnitine levels were low in muscle. During childhood, he was treated with carnitine (4-5 g daily), but without effect. With the advent of acylcarnitines, profiles mimicking but not diagnostic for multiple acyl-CoA dehydrogenase deficiency (MADD) were found. This led to treatment with riboflavin (100 mg/day for 3 years), again without effect. Clinical examination, including echocardiography, revealed no signs of involvement from other organs, and all relatives were asymptomatic.