NPC1 and Scheie syndrome: All mouse models of neurological MPS I, II, IIIA, IIIB, and IIIC, characterized by HS accumulation, exhibited strongly reduced total neuraminidase and NEU1 activity, whereas activity levels in mouse models of other LSDs were unaffected (i.e., MLD, Tay-Sachs), or even increased (i.e., NPC1, ML IV) compared with their corresponding WT littermate controls (Figure 1, F and G).