Severity estimation of very-long-chain acyl-CoA dehydrogenase deficiency via 13C-fatty acid loading test.

BACKGROUND: The clinical severity of very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is difficult to predict using conventional diagnostic methods. METHODS: Peripheral blood mononuclear cells obtained from 14 VLCAD deficiency patients and 23 healthy adults were loaded with carbon-13-universally labeled (U-13C-) fatty acids. Differences in acylcarnitine ratios between the patients and healthy groups and correlations between acylcarnitine ratios and a newly established clinical severity score (CSS) in the patient group were statistically examined. RESULTS: There was a significant decrease in the 13C-C2/13C-C18 and 13C-C12/13C-C14 ratios in the U-13C-stearic acid loading test and in the 13C-C2/13C-C18:1 and 13C-C12:1/13C-C14:1 ratios in the U-13C-oleic acid loading test in the patient group. The values of each ratio were significantly correlated with the CSS, suggesting that they could predict disease severity. Additionally, patients with a higher 13C-C16/13C-C18 ratio than the 13C-C14/13C-C18 ratio in the U-13C-stearic acid loading test had a significantly higher CSS and were presumed to have more severe disease. CONCLUSIONS: Our data indicated that this method could be used to predict the clinical severity of VLCAD deficiency, and identify patients at a risk of severe disease. IMPACT: We established a novel method to predict the severity of VLCAD deficiency by performing a loading test with carbon-13-labeled fatty acids on peripheral blood mononuclear cells. The U-13C-oleic acid loading test was useful for comparing the patient group with the control group in terms of disease severity. The U-13C-stearic acid loading test was useful for identifying the more severely affected patients. These methods are relatively less invasive and enable rapid evaluation of the clinical severity.

Evaluation of Metabolic Defects in Fatty Acid Oxidation Using Peripheral Blood Mononuclear Cells Loaded with Deuterium-Labeled Fatty Acids.

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 d27-C14-acylcarnitine/d31-C16-acylcarnitine and d23-C12-acylcarnitine/d31-C16-acylcarnitine for carnitine palmitoyltransferase-II (CPT-II) deficiency, decreased ratios of d23-C12-acylcarnitine/d27-C14-acylcarnitine for very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency, and increased ratios of d29-C16-OH-acylcarnitine/d31-C16-acylcarnitine for trifunctional protein (TFP) deficiency, together with increased ratios of d7-C4-acylcarnitine/d31-C16-acylcarnitine for carnitine palmitoyltransferase-I deficiency. The decreased ratios of d1-acetylcarnitine/d31-C16-acylcarnitine could be indicative of ß-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.