The effect of fasting, long-chain triglyceride load and carnitine load on plasma long-chain acylcarnitine levels in mitochondrial very long-chain acyl-CoA dehydrogenase deficiency

We studied a 10-year-old patient with very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency who was originally (mis)diagnosed as having systemic carnitine deficiency. He was subjected to a fasting test, a long-chain triglyceride (LCT) loading test (1.5g/kg) and an intravenous carnitine clearance test (0.25 mu mol/kg per min). Plasma acylcarnitines were analysed using a quantitative GC-CI-MS method. During fasting, all long-chain acylcarnitines with a chain length of C-14 and higher (especially C-14:1) increased dramatically. Total plasma long-chain acylcarnitine reached a concentration of 28.6 mu mol/L. LCT loading resulted in a moderate increase, mainly of the C-18 esters. The carnitine infusion, which led to a supranormal plasma free carnitine concentration, gave only a slight but generalized rise of long-chain acylcarnitines. Although only one patient could be tested, the results suggest that the accumulation of potentially toxic long-chain acylcarnitines in VLCAD deficiency is provoked by fasting, LCT loading and carnitine supplementation. Therapy should be adjusted accordingly.