Normal acylcarnitine levels during confirmation of abnormal newborn screening in long-chain fatty acid oxidation defects

We report two infants identified by tandem mass spectrometry (MS/MS) of neonatal blood spot acylcarnitines and confirmed by molecular genetic analysis to have long-chain fatty acid oxidation defects. In both cases, acylcarnitine concentrations in confirmatory plasma samples were normal. None the less, molecular testing identified trifunctional protein (TFP) deficiency (McKusick 600890) and very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency (McKusick 201475).