An adverse event (AE) is defined as any untoward medical occurrence, whether or not considered drug related. A serious AE is an AE that at any dose, results in any of the following outcomes: death; a life-threatening AE; inpatient hospitalization or prolongation of existing hospitalization; persistent or significant incapacity or substantial disruption of the ability to conduct normal life functions; a congenital anomaly/birth defect; or is an important medical event. AEs were graded using the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE), version 4.0: Grade 1 (mild), Grade 2 (moderate), Grade 3 (severe), Grade 4 (life-threatening), Grade 5 (death). TEAEs were defined as reported AEs with onset during the treatment.

Liquid chromatography-mass spectrometry/mass spectrometry-dermatan sulfate (LS-MS/MS-DS) method. For the participant previously treated with UX003 under an eIND, percent change from initial baseline was used.

Adverse event (AE): any untoward medical occurrence in a participant, whether or not considered drug related. Serious AE (SAE): an AE or suspected adverse reaction that at any dose results in any of the following outcomes: death; a life-threatening AE; inpatient hospitalization or prolongation of existing hospitalization; persistent or significant incapacity or substantial disruption of the ability to conduct normal life functions; a congenital anomaly/birth defect. Other important medical events may also, in the opinion of the Investigator, be considered SAEs. An AE was considered a TEAE if it occurred on or after the first dose, and was not present prior to the first dose, or it was present at the first dose but increased in severity during the study. Events recorded as either possibly, probably, or definitely related to treatment were categorized as related. AE severity was graded using the National Cancer Institute's Common Terminology Criteria for Adverse Events, Version 4.03.