Abstract
Because tandem mass spectrometry- (MS/MS-) based newborn screening identifies many suspicious cases of fatty acid oxidation and carnitine cycle disorders, a simple, noninvasive test is required to confirm the diagnosis. We have developed a novel method to evaluate the metabolic defects in peripheral blood mononuclear cells loaded with deuterium-labeled fatty acids directly using the ratios of acylcarnitines determined by flow injection MS/MS. We have identified diagnostic indices for the disorders as follows: decreased ratios of d(27)-C14-acylcarnitine/d(31)-C16-acylcarnitine and d(23)-C12-acylcarnitine/d(31)-C16-acylcarnitine for carnitine palmitoyltransferase-II (CPT-II) deficiency, decreased ratios of d(23)-C12-acylcarnitine/d(27)-C14-acylcarnitine for very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency, and increased ratios of d(29)-C16-OH-acylcarnitine/d(31)-C16-acylcarnitine for trifunctional protein (TFP) deficiency, together with increased ratios of d(7)-C4-acylcarnitine/d(31)-C16-acylcarnitine for carnitine palmitoyltransferase-I deficiency. The decreased ratios of d(1)-acetylcarnitine/d(31)-C16-acylcarnitine could be indicative of β-oxidation ability in patients with CPT-II, VLCAD, and TFP deficiencies. Overall, our data showed that the present method was valuable for establishing a rapid diagnosis of fatty acid oxidation disorders and carnitine cycle disorders and for complementing gene analysis because our diagnostic indices may overcome the weaknesses of conventional enzyme activity measurements using fibroblasts or mononuclear cells with assumedly uncertain viability.