Multiplex Tandem Mass Spectrometry Enzymatic Activity Assay for Newborn Screening of the Mucopolysaccharidoses and Type 2 Neuronal Ceroid Lipofuscinosis

Abstract

We expanded the use of tandem mass spectrometry combined with liquid chromatography (LC-MS/MS) for multiplex newborn screening of seven lysosomal enzymes in dried blood spots (DBS). The new assays are for enzymes responsible for the mucopolysaccharidoses (MPS-I, -II, -IIIB, -IVA, -VI, and -VII) and type 2 neuronal ceroid lipofuscinosis (LINCL). New substrates were prepared and characterized for tripeptidyl peptidase 1 (TPP1), α-N-acetylglucosaminidase (NAGLU), and lysosomal β-glucuronidase (GUSB). These assays were combined with previously developed assays to provide a multiplex LC-MS/MS assay of 7 lysosomal storage diseases. Multiple reaction monitoring of ion dissociations for enzyme products and deuterium-labeled internal standards was used to quantify the enzyme activities. Deidentified DBS samples from 62 nonaffected newborns were analyzed to simultaneously determine (run time 2 min per DBS) the activities of TPP1, NAGLU, and GUSB, along with those for α-iduronidase (IDUA), iduronate-2-sulfatase (I2S), N-acetylgalactosamine-6-sulfatase (GALNS), and N-acetylgalactosamine-4-sulfatase (ARSB). The activities measured in the 7-plex format showed assay response-to-blank-activity ratios (analytical ranges) of 102-909 that clearly separated healthy infants from affected children. The new multiplex assay provides a robust comprehensive newborn screening assay for the mucopolysaccharidoses. The method has been expanded to include additional lysosomal storage diseases.