The purpose of the study is to evaluate the ability of rhASB versus placebo to enhance endurance in patients with Mucopolysaccharidosis VI (MPS VI), as evidenced by an increase in the number of meters walked in the 12 minute walk test at Week 24 compared with baseline.

Inclusion Criteria

• Patient consent
• Patient must be seven years of age or older
• Patient must have documented biochemical or genetic proof of MPS VI
• The patient must be able to walk independently at least 5 meters and no more than 270 meters in the first 6 minutes, or no more then 400 meters total in 12 minutes, in the screening 12-minute walk test
• If female of childbearing potential, patient must have a negative pregnancy test

Exclusion Criteria

• Patient is under consideration for or has undergone a successful bone marrow transplant (BMT)
• Patient refuses or is unable to complete all screening evaluations
• Pregnant or lactating patient
• Patient has received an investigational drug within 30 days prior to study enrollment
• Patient has been previously treated with rhASB
• Patient has a medical condition, serious intercurrent illness, or other extenuating circumstance that may significantly confound study results or decrease study compliance
• The patient has clinically significant spinal cord compression
• The patient has known hypersensitivity to rhASB or to components of the active or placebo test solutions