Identification of undescribed medium-chain acylcarnitines present in urineof patients with propionic and methylmalonic acidemias

In urine of patients with propionyl-CoA carboxylase deficiency or with meth ylmalonic acidemia, carnitine esters of 2-methyl-branched fatty acids of al l chain lengths between 4 and 9 atoms of carbon were identified during the acute phase of the diseases. The chemical structure of these compounds was obtained by gas chromatography-mass spectrometry analysis of their fatty ac id moieties in their free and picolinyl ester forms. We suggest mechanisms for the biosynthesis of these branched fatty acids, and their accumulation in urine during episodes of caloric imbalance. (C) 2000 Elsevier Science B. V. All rights reserved.