Research Notes: Acylcarnitines

Pediatr Res. 2003 Aug.
Rare disorders of metabolism with elevated butyryl- and isobutyryl-carnitine detected by tandem mass spectrometry newborn screening.
Koeberl DD, Young SP, Gregersen NS, Vockley J, Smith WE, Benjamin DK Jr, An Y, Weavil SD, Chaing SH, Bali D, McDonald MT, Kishnani PS, Chen YT, Millington DS.
Division of Medical Genetics, DUMC 3528, Bell Building Room 237, Trent Duke University Medical Center, Durham, NC, U.S.A.

Tandem mass spectrometry was adopted for newborn screening by North Carolina in April 1999. Since then, three infants with short-chain acyl-CoA dehydrogenase (SCAD) and one with isobutyryl-CoA dehydrogenase deficiency were detected on the basis of elevated butyrylcarnitine/isobutyrylcarnitine (C4-carnitine) concentrations in newborn blood spots analyzed by tandem mass spectrometry. For three SCAD-deficient infants, biochemical evaluation included a plasma acylcarnitine profile with markedly elevated C4-carnitine, urine organic acid analysis with markedly elevated ethylmalonic and 2-methylsuccinic acids, and markedly elevated [U-13C]butyrylcarnitine concentrations in medium from fibroblasts incubated with [U-13C]palmitic acid and excess l-carnitine, consistent with classic SCAD deficiency. Two of three infants diagnosed with classic SCAD deficiency remained asymptomatic; however, the third infant presented with seizures and a cerebral infarct at 10 wk of age. All three infants had putatively inactivating mutations in both alleles of the SCAD gene. The highly elevated plasma C4-carnitine levels in the three infants detected by newborn screening tandem mass spectrometry differentiated them from infants and children who were homozygous or compound heterozygous for one of two SCAD gene susceptibility variations; for the latter group the C4-carnitine levels were normal. Isobutyryl-CoA dehydrogenase deficiency in a fourth infant was confirmed after isolated elevation of C4-carnitine in the acylcarnitine profile.

Mol Genet Metab. 1998 Dec.
Isolated isobutyryl-CoA dehydrogenase deficiency: an unrecognized defect in human valine metabolism.
Roe CR, Cederbaum SD, Roe DS, Mardach R, Galindo A, Sweetman L.
Institute of Metabolic Disease, Baylor University Medical Center, Dallas, Texas.

A 2-year-old female was well until 12 months of age when she was found to be anemic and had dilated cardiomyopathy. Total plasma carnitine was 6 microM and acylcarnitine analysis while receiving carnitine supplement revealed an increase in the four-carbon species. Urine organic acids were normal. In vitro analysis of the mitochondrial pathways for beta oxidation, and leucine, valine, and isoleucine metabolism was performed in fibroblasts using stable isotope-labeled precursors to these pathways followed by acylcarnitine analysis by tandem mass spectrometry. 16-2H3-palmitate was metabolized normally down to the level of butyryl-CoA thus excluding SCAD deficiency. 13C6-leucine and 13C6-isoleucine were also metabolized normally. 13C5-valine incubation revealed a significant increase in 13C4-isobutyrylcarnitine without any incorporation into propionylcarnitine as is observed normally. These same precursors were also evaluated in fibroblasts with proven ETF-QO deficiency in which acyl-CoA dehydrogenase deficiencies in each of these pathways was clearly identified. These results indicate that in the human, there is an isobutyryl-CoA dehydrogenase which exists as a separate enzyme serving only the valine pathway in addition to the 2-methyl branched-chain dehydrogenase which serves both the valine and the isoleucine pathways in both rat and human.

Acta Paediatr Jpn. 1994 Apr.
A study of urinary metabolites in patients with dicarboxylic aciduria for differential diagnosis.
Shimizu N, Yamaguchi S, Orii T.
Department of Pediatrics, Gifu University School of Medicine, Japan.

Dicarboxylic aciduria (DCA-uria) is a relatively common finding in the screening of organic acidemias by gas chromatography/mass spectrometry (GC/MS). A considerable number of patients with DCA-uria are involved in disturbances of mitochondrial and peroxisomal fatty acid beta-oxidation. The differential diagnosis of DCA-uria was investigated using a combination of organic acid analysis by GC/MS, carnitine determination, acylcarnitines by fast atom bombardment/mass spectrometry (FAB/MS) and acylglycines by stable-isotope dilution analysis. The relative distribution of urinary metabolites was examined in 46 patients with DCA-uria of different origins, including physiological ketosis of childhood, disorders of propionic acid metabolism, glutaric aciduria type II, Zellweger syndrome and patients who were clinically diagnosed as having Reye syndrome. Zellweger syndrome seemed to be distinguishable from other disorders by the high sebacic acid/adipic acid ratio of DCA-uria and increased excretion of 4-hydroxyphenyllactic acid and 2-hydroxysebacic acid. The mild form of glutaric aciduria type II was often missed by current organic acid analysis alone, but was readily diagnosed by acylcarnitine and acylglycine determination. The ratio of free/total carnitine was low in most of the DCA-uria patients except for two of five cases of Zellweger syndrome and one of three cases of Reye syndrome. The acylcarnitine analysis by FAB/MS showed adipyl-, suberyl-, sebacyl- or dodecanedioylcarnitine as major peaks in most of these patients, although these were not specific. Disease-specific peaks were detectable only in congenital organic acidemias such as glutaric aciduria type II, methylmalonic acidemia and propionic acidemia.

Pediatr Res. 1984 Dec.
Urinary excretion of l-carnitine and acylcarnitines by patients with disorders of organic acid metabolism: evidence for secondary insufficiency of l-carnitine.
Chalmers RA, Roe CR, Stacey TE, Hoppel CL.

Concentrations of l-carnitine and acylcarnitines have been determined in urine from patients with disorders of organic acid metabolism associated with an intramitochondrial accumulation of acyl-CoA intermediates. These included propionic acidemia, methylmalonic aciduria, isovaleric acidemia, multicarboxylase deficiency, 3-hydroxy-3-methylglutaric aciduria, methylacetoacetyl-CoA thiolase deficiency, and various dicarboxylic acidurias including glutaric aciduria, medium-chain acyl-CoA dehydrogenase deficiency, and multiple acyl-CoA dehydrogenase deficiency. In all cases, concentrations of acylcarnitines were greatly increased above normal with free carnitine concentrations ranging from undetectable to supranormal values. The ratios of acylcarnitine/carnitine were elevated above the normal value of 2.0 +/- 1.1. l-Carnitine was given to three of these patients; in each case, concentrations of plasma and urine carnitines increased accompanied by a marked increase in concentrations of short-chain acylcarnitines. These acylcarnitines have been examined using fast atom bombardment mass spectrometry in some of these diseases and have been shown to be propionylcarnitine in methylmalonic aciduria and propionic acidemia, isovalerylcarnitine in isovaleric acidemia, and hexanoylcarnitine and octanoylcarnitine in medium-chain acyl-CoA dehydrogenase deficiency. The excretion of these acylcarnitines is compatible with the known accumulation of the corresponding acyl-CoA esters in these diseases. In this group of disorders, the increased acylcarnitine/carnitine ratio in urine and plasma indicates an imbalance of mitochondrial mass action homeostasis and, hence, of acyl-CoA/CoA ratios. Despite naturally occurring attempts to increase endogeneous l-carnitine biosynthesis, there is insufficient carnitine available to restore the mass action ratio as demonstrated by the further increase in acylcarnitine excretion when patients were given oral l-carnitine.