Slightly changed or unchanged DPP-IV activity was detected in patients with Gaucher disease (not treated), ceroid lipofuscinosis type 1 (CLN1; n = 1), Niemann–Pick type C and A, Krabbe, Pompe diseases (not treated), gangliosidosis GM2 and metachromatic leukodystrophy (MLD). This evidence concerns the gene PPT1 and metachromatic leukodystrophy.