Total Ion Chromatogram profiles of 4-MU at constant concentration of internal standard obtained with TripleQuad MRM-MSfor

<p>A—a blank sample or filter paper incubated in the same manner as the blood samples (that contain 4-MU present at the beginning of the enzymatic reaction as a byproduct of the synthesis); B—pathological blood sample (with similar TIC profile as the blank sample, used as a quality control in each assay); C—a normal activity blood sample (healthy control with an average GALNS activity used as a quality control in each assay); D—a high activity blood sample (a sample with atypically high activity of lysosomal enzymes).