RAPID DIAGNOSIS OF MAPLE-SYRUP-URINE-DISEASE IN BLOOD SPOTS FROM NEWBORNS BY TANDEM MASS-SPECTROMETRY

We report a new method for the diagnosis of maple syrup urine disease (MSUD) from dried blood spots on newborn screening cards based on tand em mass spectrometry (MS-MS). The mean +/- SD concentration of Leu plu s lie in normal newborns was 151 +/- 47 mu mol/L (n = 1096); for Val, 131 +/- 58 mu mol/L (n = 791). SDs were lower when the concentrations of these amino acids were expressed relative to that of Phe. The mean ratio for Leu + Ile to Phe was 2.5 +/- 0.49; for Val to Phe, 2.18 +/- 0.51. These results compare well with values previously reported in th e literature. With these criteria, samples from a collection categoriz ed by a bacterial inhibition assay as normal or falsely positive for M SUD were normal by MS-MS [(Leu + Ile):Phe <5.0]. Samples from confirme d MSUD patients were categorized as abnormal [(Leu + Ile):Phe >9.0] by MS-MS.