Very high DPP-IV activity was found in patients with mucolipidosis type II/III (over 5 MoM or 20 MoM in Warsaw or Moscow, respectively), alpha-mannosidosis (4.87 MoM, Warsaw) and mucopolysaccharidosis type II (6.06 MoM in Moscow and 3.16 MoM in Warsaw). This evidence concerns the gene DPP4 and mucolipidosis type II.