Leukocyte and Dried Blood Spot Arylsulfatase A Assay by Tandem Mass Spectrometry.

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay utilizing deuterated natural sulfatide substrate to measure arylsulfatase A (ARSA) activity in leukocytes and dried blood spot (DBS) was developed and validated. These new assays were highly specific and sensitive. Patients with metachromatic leukodystrophy (MLD) and multiple sulfatase deficiency (MSD) demonstrated clear deficit in the enzymatic activity, and can be completely distinguished from normal controls. The leukocyte assay reported here was important for diagnosing MLD and MSD patient and for monitoring the efficacy of therapeutic treatments. On the other hand, ARSA activity was measured in DBS for the first time without an antibody. Currently, this new ARSA DBS assay serves as a second-tier test following sulfatide measurement in DBS for newborn screening of MLD, leading to an elimination of most of the false positives identified by the sulfatide assay. We are also evaluating its potential as the first-tier test for the newborn sc...