Diagnosis of isovaleric acidaemia by tandem mass spectrometry: false positive result due to pivaloylcarnitine in a newborn screening programme.

Tandem mass spectrometric analysis of acylcarnitines and amino acids has been applied in newborn screening programmes for the detection of several inborn errors of metabolism. We report a false positive result for isovaleric acidaemia in a newborn screening programme using this method. The newborn screening sample showed a very prominent signal corresponding to the mass of isovalerylcarnitine. Repeat samples (age 6 days) of blood and urine showed similar results. However, urine organic acids were normal. Acylcarnitine analysis in blood, breast milk and urine of the mother also showed a prominent signal of the same mass. Gas chromatography-mass spectrometry of the methyl esters demonstrated that the signal in the patient's urine was due to the presence of pivaloylcarnitine, which is isomeric with isovalerylcarnitine. The patient's mother was receiving an antibiotic containing a derivative of pivalic acid to treat a urinary tract infection. Follow-up samples in the patient and the mother confirmed a decrease in the levels of pivaloylcarnitine, concomitant with the discontinuation of the treatment. We conclude that pivaloylcarnitine can give a false positive result for isovaleric acidaemia in newborns whose mothers are on treatment with pivoxilsulbactam-containing antibiotics.

Isovaleric acidemia: response to a leucine load after three weeks of supplementation with glycine, L-carnitine, and combined glycine-carnitine therapy.

OBJECTIVE: To assess the effectiveness of glycine and carnitine therapy on isovaleryl conjugate excretion in isovaleric acidemia (IVA). STUDY DESIGN: Urinary isovalerylglycine (IVG) and isovalerylcarnitine (IVC) were measured from 12-hour urine specimens collected overnight from an 8-year-old patient with IVA (who had no residual activity of isovaleryl-CoA dehydrogenase in fibroblasts) before and during 3-week courses of supplementation with glycine alone (250 mg/kg per day), L-carnitine alone (100 mg/kg per day) therapy, and both of these agents combined, with a 2 gm leucine challenge performed at the end of each treatment period. RESULTS: Isovalerylglycine was the predominant metabolite excreted throughout the study, and its mean value doubled with glycine treatment. Isovalerylcarnitine excretion was minimal without carnitine supplementation. L-Carnitine therapy was associated with a 50% decline in excretion of IVG without a fully compensatory increase in IVC. The readdition of glycine to the carnitine regimen resulted in an increase in IVG excretion. Leucine challenge resulted in a 2.7- and 2.4-fold increase of IVG and IVC excretion, respectively, during L-carnitine therapy but not during glycine supplementation, and a 3.5- and 4-fold increase in excretion of both metabolites during glycine plus L-carnitine therapy. Total conjugate excretion was highest after a leucine load during combined glycine and L-carnitine therapy. CONCLUSIONS: Combined glycine and L-carnitine therapy maximally increases isovaleryl conjugate excretion during metabolic stress but not under stable conditions.

Lessons from the late diagnosis of isovaleric acidemia in a five-year-old boy.

Chronic, intermittent isovaleric acidemia was undiagnosed in a boy with an increased anion gap metabolic acidosis until the boy was 5 years of age. This case emphasizes the importance of maintaining a high index of suspicion for inborn errors of metabolism in patients with metabolic acidosis, even in late childhood.

[Phenotypic expression variation of isovaleric acidemia in Argentinian patients. A long term follow-up]. / Variación en la expresión fenotípica de la acidemia isovalérica en pacientes argentinos. Observaciones de un prolongado seguimiento.

In this paper we discuss the first five Argentinean patients presenting isovaleric acidemia (IVA), an alteration of leucine catabolism due to a genetic defect of isovaleryl-CoA dehydrogenase. Belonging to unrelated families, one from native (H. Fam.) and the other from Italian ancestry (M. Fam.); the patients presented the clinical pattern highly suggestive of the disease: they were siblings, had disease-free intervals, vomiting, ketoacidosis crises, "sweaty feet" odor and progression of the neurologic involvement from somnolence and stupor to profound coma. In the four children of H. Fam. the disease had a late but severe beginning; one of the girls died (N.H.). The boy from M. Fam. presented a neonatal form of clearly benign course. The disease was confirmed by gas-chromatography (GC) of volatile acids in serum and also by the typical urinary acid GC-profiles (Fig. 1, A and B); the isovalerylglycine quantitative evaluation in urinary samples collected during crises is shown in Table 1. The morphological findings in liver and brain of N.H. showed at the ultrastructural study, an extensive fatty degeneration and greatly marked mitochondrial alterations in the liver and edema, neuronal karyorrhexis and karyolysis in the brain (Fig. 2). The therapeutic protocol based on a low leucine or low protein diet and use of glycine is described. The evolutionary follow up, more than 10 years for the first case, showed a normal mental development in three of them and retardation in the first child of H. Fam., who had a late diagnosis. IVA is still valuable as a paradigm in the acquisition of a highly clinical suspicion and for its introduction in the study of genetic organic acidemias.