AGT-181 is a fusion protein containing alpha-L-iduronidase that is intended to deliver the enzyme peripherally and to the brain, when administered intravenously.

This is a long term safety and tolerability study of AGT-181 in patients with MPS I who completed the previous 26-week study, AGT-181-101. Information on the biological activity of the investigational drug will also be collected.

AGT-181-101E is a safety and tolerability study of AGT-181 in patients with MPS I who completed the previous 26-week study, AGT-181-101. Information on the biological activity of the investigational drug will be collected as well as longitudinal safety information.

Inclusion Criteria:

• 2 years of age or older (and less than 18)
• Must have been previously enrolled in study AGT-181-101
• Written consent and assent as required
• Female patients must not be pregnant, willing to utilize appropriate birth control methods and undergo pregnancy testing during the study

Exclusion Criteria:

• Refusal to complete all assessments
• Pregnant or Lactating
• Received investigational drug within 1 year prior to study enrollment
• Medical condition or extenuating circumstance that, in the opinion of the investigator, may interfere with study compliance
• Clinically significant spinal cord compression or evidence of cervical instability (i.e. expected to require intervention during study participation)
• Has developed clinically relevant hypersensitivity/anaphylactoid reactions to AGT-181