Tandem Mass Spectrometric Analysis of Dried Blood Spots for Screening of Mucopolysaccharidosis I in Newborns

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Abstract
Mucopolysaccharidosis type I (MPS-I), caused by a deficiency of α-l-iduronidase (IDUA; EC 3.2.1.76) activity, can manifest as three major phenotypes, usually defined by clinical criteria: Hurler (severe), Scheie (mild), and Hurler–Scheie (intermediate) syndromes. IDUA is crucial for degradation of glycosaminoglycans such as dermatan and heparan sulfate. Failure to break down these polysaccharides causes physical changes such as joint stiffness, skeletal abnormalities, and corneal clouding. Hurler syndrome is characterized by valvular heart disease, mental deterioration, and death in childhood. Enzyme replacement therapy has been developed for MPS-I, and bone marrow transplantation is beneficial if performed early (1). Because early detection is necessary for optimum clinical response to therapy, the need for newborn screening of MPS-I is under active discussion. Lysosomal enzymes can be measured in rehydrated dried blood spots (DBS) (2)(3)(4)(5)(6)(7)(8). Fluorometric, radiometric, and electrospray ionization tandem mass spectrometry (ESI-MS/MS) assays have been developed. The latter offer the capability of assaying the products of several enzymes simultaneously (multiplexing) (8). In this report, we describe an ESI-MS/MS assay that directly measures the reaction velocity of IDUA in rehydrated DBS for the newborn screening of MPS-I. We also show that the assay can be combined with ESI-MS/MS assays of Niemann–Pick type A/B, Krabbe, Gaucher, Pompe, and Fabry diseases (8) for the simultaneous analysis of six lysosomal storage diseases. All experiments with DBS were conducted in compliance with Institutional Review Board review. All MPS-I-affected patients had been diagnosed previously with established clinical and biochemical procedures. DBS were kept at ambient temperature during shipment (<10 days) and then stored at −20 °C in zip-lock plastic bags (one bag sealed inside of a second bag). Zip-lock bags were kept in a sealed plastic box containing desiccant (anhydrous CaSO4 granules). We developed …