Urinary GAGs and specific lysosomal enzymes have been the only biomarkers for MPS, although recent studies identified serum heparin cofactor II-thrombin (HCII-T) as a biomarker for MPS I, II and III [33], dipeptidyl peptidase IV (DPP-IV) for MPS I, II, III, IVA and VI [34], and recently the potential of disease-specific non-reducing end carbohydrate biomarkers for MPS [35]. This evidence concerns the gene DPP4 and mucopolysaccharidosis.