NEU1 and mucolipidosis type IV: To test whether the secondary deficiency of NEU1 is shared by other lysosomal disorders, we analyzed total neuraminidase and NEU1 activities in the brain tissues of available MPS mouse models (MPS I, II, IIIA, IIIB, and IVA) and models of other neurological LSDs (namely, metachromatic leukodystrophy [MLD], Tay-Sachs, Niemann-Pick type C1 [NPC1], and mucolipidosis IV [ML IV]).