Pseudo-glutarylcarnitinaemia in medium-chain acyl-CoA dehydrogenase deficiency detected by tandem mass spectrometry newborn screening

As well as characteristic increases in C-8 carnitine, dried blood spot samples from 11 newborns with medium-chain acyl-CoA dehydrogenase deficiency detected by tandem mass spectrometry screening using butyl esters showed apparent increases in glutarylcarnitine (m/z 388 signals). In four of the newborns in which it was measured, apparent increases in malonylcarnitine (m/z 360) were also detected. It was shown that the apparent increases were caused by interfering acylcarnitines, putatively identified as hydroxyoctanoylcarnitine and hydroxydecanoylcarnitine, respectively, using alternative derivatives for tandem mass spectrometry. Levels of the two abnormal carnitines correlated with C-8 carnitine levels and normalized with repeat testing in 10 cases. These results indicated that the abnormal carnitines were significantly elevated only during periods of increased fatty acid catabolism, as may occur in the immediate postnatal period.