Newborn screening programs for inherited diseases are well established in many developed countries. Dried blood spots on screening cards are collected from newborns for early detection of diseases and improvement of their health. Before the recent application of tandem mass spectrometry (MS-MS) to newborn screening, one test on one sample of blood was used to screen a single disease, phenylketonuria (PKU), which was screened originally by a bacterial inhibition assay of phenylalanine.
However, MS-MS enables the sensitive and quantitative analysis of many ionic compounds with high polarity, such as acylcarnitines and amino acids, in a single process. The first proposal of this technology for newborn screening was reported in 1990. More than 30 inborn errors of metabolism (IEM) in the categories of fatty acid oxidation disorders, organic acidemias, and aminoacidopathies can be diagnosed simultaneously by MS-MS measurement of one small punch of a blood spot. In clinical settings, fatty acid oxidation disorders and organic acidemias were known to cause sudden death in infancy, which could be prevented by early recognition of these diseases by MS-MS. The phenylalanine/ tyrosine ratio determined by MS-MS was demonstrated to be a sensitive marker in PKU screening among newborns discharged from hospitals less than 24 hr. Thus the use of MS-MS technology has expanded rapidly into newborn screening.
However, most target diseases in MS-MS screening are rather rare and heterogeneous in clinical severity, and the screening's clinical validity, clinical utility, and cost-effectiveness have not yet been fully established. Further careful data collection regarding the sensitivity of MS-MS screening and outcomes of patients in whom disorders are detected is required.
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