title: Tandem Mass Spectrometry Has a Larger Analytical Range than Fluorescence Assays of Lysosomal Enzymes: Application to Newborn Screening and Diagnosis of Mucopolysaccharidoses Types II, IVA, and VI.
abstract: BACKGROUND
  There is interest in newborn screening and diagnosis of lysosomal storage diseases because of the development of treatment options that improve clinical outcome. Assays of lysosomal enzymes with high analytical range (ratio of assay response from the enzymatic reaction divided by the assay response due to nonenzymatic processes) are desirable because they are predicted to lead to a lower rate of false positives in population screening and to more accurate diagnoses.
  
  
  METHODS
  We designed new tandem mass spectrometry (MS/MS) assays that give the largest analytical ranges reported to date for the use of dried blood spots (DBS) for detection of mucopolysaccharidoses type II (MPS-II), MPS-IVA, and MPS-VI. For comparison, we carried out fluorometric assays of 6 lysosomal enzymes using 4-methylumbelliferyl (4MU)-substrate conjugates.
  
  
  RESULTS
  The MS/MS assays for MPS-II, -IVA, and -VI displayed analytical ranges that are 1-2 orders of magnitude higher than those for the corresponding fluorometric assays. The relatively small analytical ranges of the 4MU assays are due to the intrinsic fluorescence of the 4MU substrates, which cause high background in the assay response.
  
  
  CONCLUSIONS
  These highly reproducible MS/MS assays for MPS-II, -IVA, and -VI can support multiplex newborn screening of these lysosomal storage diseases. MS/MS assays of lysosomal enzymes outperform 4MU fluorometric assays in terms of analytical range. Ongoing pilot studies will allow us to gauge the impact of the increased analytical range on newborn screening performance.
authors.affiliation: Departments of Chemistry.
authors.forename: Arun Babu
authors.initials: AB
authors.lastname: Kumar
authors.affiliation: Departments of Chemistry.
authors.forename: Sophia
authors.initials: S
authors.lastname: Masi
authors.affiliation: Departments of Chemistry.
authors.forename: Farideh
authors.initials: F
authors.lastname: Ghomashchi
authors.affiliation: Departments of Chemistry.
authors.forename: Naveen Kumar
authors.initials: NK
authors.lastname: Chennamaneni
authors.affiliation: Department of Bioscience and Biotechnology, Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Ito
authors.affiliation: Pediatrics, and.
authors.forename: C Ronald
authors.initials: CR
authors.lastname: Scott
authors.affiliation: Departments of Chemistry.
authors.forename: Frantisek
authors.initials: F
authors.lastname: Turecek
authors.affiliation: Departments of Chemistry, Biochemistry, University of Washington, Seattle, WA; gelb@chem.washington.edu spacil@u.washington.edu.
authors.forename: Michael H
authors.initials: MH
authors.lastname: Gelb
authors.affiliation: Departments of Chemistry, gelb@chem.washington.edu spacil@u.washington.edu.
authors.forename: Zdenek
authors.initials: Z
authors.lastname: Spacil
mesh_terms: D059788:Dried Blood Spot Testing / Q000379:methods*; D005470:Fluorometry; D006801:Humans; D007231:Infant, Newborn; D009083:Mucopolysaccharidoses / Q000097:blood / Q000175:diagnosis*; D015997:Neonatal Screening / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D053719:Tandem Mass Spectrometry / Q000379:methods*