4-Methylumbelliferyl 2-Acetamido-2-deoxy-α-D-galactopyranoside PEG Ether is a polymer derivative of GalNAc1-α-4MU (M333500), an effective substrate for the detection of N-acetyl-α-D-Galactopyranosiaminidase activity. The deficiency of this enzyme is the defect in Schindler disease.