At present, MPS-VI is mostly treated by enzyme replacement therapy (ERT), i.e. weekly infusion of the recombinant human ARSB (rhARSB) modified with mannose 6-phosphate (M6P) residues to allow M6P receptor-mediated cellular uptake and lysosomal delivery (12,13). The gene discussed is ARSB; the disease is mucopolysaccharidosis type 6.