In summary, median DPP-IV activity, as well as median DPP-IV MoM, were significantly elevated in all types of mucopolysaccharidoses (MPS), alpha-mannosidosis, sialidosis, gangliosidosis GM1, mucolipidosis type II/III (ML II/III), Wolman/CESD, multiple sulphatase deficiency (MSD) and ceroid lipofuscinosis type 2 (CLN2) as compared to controls. The gene discussed is DPP4; the disease is mucolipidosis type II.