Madsen KL, et al. - In patients with primary carnitine deficiency (PCD) with and without L-carnitine treatment, researchers studied energy metabolism during exercise. In this interventional study, they enrolled 8 adults with PCD who were homozygous for the c.95A>G (p.N32S) mutation and 10 healthy age- and sex-matched controls. In patients with L- carnitine treatment during exercise, the total fatty acid oxidation rate was higher than without treatment. During exercise, PCD patients have limited oxidation of fat. During exercise, L- carnitine treatment might not only prevent cardiac complications in asymptomatic patients with PCD but also increase skeletal muscle fat metabolism.