The invention relates to a method of treating mucopolysaccharidoses using enzyme replacement therapy with chemically modified lysosomal enzymes. More specifically the method relates to administering chemically modified lysosomal enzymes intraperitoneal injection. In addition, the invention relates to treating type VII mucopolysaccharidoses or mucopolysaccharidoses type VII related bone lesions with a chemical modified β-glucuronidase, wherein the modified β-glucuronidase may be administered 5 weeks after birth, and or may be administered intraperitoneally.
