3-HYDROXYISOVALERYLCARNITINE IN PATIENTS WITH DEFICIENCY OF 3-METHYLCROTONYL COA CARBOXYLASE

Highly elevated urinary acylcarnitine levels (range: 27.1-1314.0; norm al: < 30 mmol/mol creatinine) combined with a generalized, severe decr ease of free carnitine before treatment in six patients of two familie s with an isolated biotin-unresponsive deficiency of 3-methyl-crotonyl CoA:carboxylase (3-methylcrotonyl-CoA:carbon dioxide ligase; EC 6.4.1 .4) prompted the study to specify the acyl moities attached to the car rier molecule carnitine. Only traces of 3-methylcrotonyl carnitine (1. 3-2.2% of total ester concentration) were found by high performance li quid chromatography, whereas the prominent species determined by fast- atom bombardment/tandem mass spectrometry and gas chromatography-mass spectrometry corresponded to a hydroxy five-carbon-acylcarnitine. Crud e urine samples were derivatized directly and the resulting N-demethyl carnitine-propylester and trimethylsilylesters/ethers of intact acylca rnitines analyzed by gas chromatography-mass spectrometry. Mass spectr a acquired by both chemical ionization and electron impact gave both t he molecular weight and fragmentation patterns consistent with that ex pected for 3-hydroxyisovaleryl carnitine. In addition, acylcarnitines were extracted from urine, hydrolyzed and the trimethylsilyl-derivativ es of the organic acids analyzed by gas chromatography-mass spectromet ry. Free 3-hydroxyisovaleric acid found in the hydrolyzed sample and n ot in an unhydrolyzed one confirmed the suggested acyl group.