Carnitine intake and excretion in neuromuscular disease

Free and total carnitine serum concentrations and urinary excretion were examined in patients with various neuromuscular diseases. On a measured, low carnitine diet and during fasting, the patients did not differ from controls. Carnitine excretion in patients (3.08 ± 1.87 μmol/kg/day) and controls (2.99 ± 1.12) exceeded carnitine intake (patients, 2.35 ± 0.94 μmol/kg/day; controls 1.33 ± 0.70). Because of heterogeneity in the patient population, carnitine excretion was assessed according to creatinine excretion, chosen as an indicator of muscle mass. Those patients with daily creatinine excretion < 1 g/day had significantly lower carnitine excretion (106 ± 47 versus 205 ± 95 μmol/day, p<0.05), and there was a positive correlation between creatinine excretion and carnitine excretion (r=0.82) and between muscle carnitine and carnitine excretion (r=0.67). Urinary clearances for acylcarnitine were 10 to 20 times higher than those for free carnitine. Two patients with carnitine palmityl transferase deficiency were similar to the other patients, but the carnitine-deficient patient lost excessive carnitine during fasting, probably secondary to an elevated acylcarnitine fraction in the blood.