Carnitine intake and excretion in neuromuscular diseases.

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 (3.09 +/- 1.87 mumol/kg/day) and controls (2.99 +/- 1.12) exceeded carnitine intake (patients, 2.35 +/- 0.94 mumol/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 less than 1 g/day had significantly lower carnitine excretion (106 +/- 47 versus 205 +/- 95 mumol/day, p less than 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 and 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 elevated acylcarnitine fraction in the blood.