Second-Tier Test for Quantification of Alloisoleucine and Branched-Chain Amino Acids in Dried Blood Spots to Improve Newborn Screening for Maple Syrup Urine Disease (MSUD)

Abstract

BACKGROUND:Newborn screening for maple syrup urine disease (MSUD) relies on finding increased concentrations of the branched-chain amino acids (BCAAs) leucine, isoleucine, and valine by tandem mass spectrometry (MS/MS). D-Alloisoleucine (alloIle) is the only pathognomonic marker of MSUD, but it cannot be identified by existing screening methods because it is not differentiated from isobaric amino acids. Furthermore, newborns receiving total parenteral nutrition often have increased concentrations of BCAAs. To improve the specificity of newborn screening for MSUD and to reduce the number of diet-related falsepositive results, we developed a LC-MS/MS method for quantifying allo-Ile.

Determination of Total Homocysteine, Methylmalonic Acid, and 2-Methylcitric Acid in Dried Blood Spots by Tandem Mass Spectrometry

“…Determination of analyte ratios, such as the C3/C2 ratio, and consideration of these ratios for the interpretation of abnormal C3-AC concentrations can help to reduce the number of false-positive results (6 ). However, only the measurement of pathognomonic analytes can markedly improve the balance between the diagnostic sensitivity and specificity of the test for nonspecific biomarkers (10,(22)(23)(24). Sometimes disease-specific markers such as succinylacetone can be included in routine screening (25,26 ) or a condition is sufficiently prevalent in a defined population, justifying specific testing of every newborn (8 ).…”

Dried blood spot sampling in combination with LC‐MS/MS for quantitative analysis of small molecules

“…Listed in Table 1 are some representative applications in the primary and/or confi rmatory newborn screening for the diagnosis of some inherited metabolic disorders, including congenital adrenal hyperplasia (CAH), hyperhomocysteinemia, tyrosinemia type 1, methylmalonic acidemia and homocytinuria, etc. (Janzen et al, 2007;Lacey et al, 2004;la Marca et al, 2008c;McCann et al, 2003;Oglesbee et al, 2008;Zoppa et al, 2006). There are many situations in newborn screening where absolute concentration of a single biomarker molecule may not be diagnostic; instead, accurate quantifi cation of multiple biomarker molecules using LC-MS/MS, followed by comparison of response ratios of one species to the other(s), is more powerful (Carpenter and Wiley, 2002).…”

“…However, the specifi city of MS/MS assay alone (infusion or fl ow injection) is often hampered by interferences of the matrix components, especially those sharing the same MS/MS transitions with the target analytes. The presence of isomeric and/or isobaric interference components has been reported to contribute to the higher incidences of false-positive results from the measurement of branch-chain amino acids, isovalerylglycine and C 4 /C 5 acylcarnitines that are, respectively, associated with the diagnosis of maple syrup urine disease, isovaleric academia and short-chain acyl-coenzyme A dehydrogenase defi ciency (Abdenur et al, 1998;Chace et al, 1995;Garg and Dasouki, 2006;Oglesbee et al, 2008;Shigematsu et al, 1999 and2007). Furthermore, the possible in-source fragmentation in the case that the target analyte is a derivative of another intact biomarker molecule and natural isotope contribution might add another challenge to MS/MS (infusion or fl ow injection) only assays (Garg and Dasouki, 2006;Piraud et al, 2003).…”

A Quantitative Method for the Measurement of Dried Blood Spot Amino Acids Using Ultra-Performance Liquid Chromatography

“…The measurement of amino acids in dried blood spots has been extensively used for the detection of newborns with various inborn errors of amino acid metabolism including phenylketonuria (PKU) 3 and maple syrup urine disease (MSUD). Dried blood spots are a convenient tool for the diagnosis of certain inborn errors of metabolism; however, their utility in regular monitoring of amino acids has been limited.…”