Part A (Initial therapy): Participants received SBC-103, 0.3, 1.0, or 3.0 mg/kg QOW for 24 weeks, followed by a ≥ 4-week treatment break. Participants enrolled in the lowest dosage first.

Part B: Participants were escalated to the next highest dose that was considered safe (1.0 or 3.0 mg/kg QOW) for ≥ 8 weeks. Participants who received doses of 0.3 mg/kg in Part A were considered for a second dose escalation to 3.0 mg/kg at any time during Part B provided that they tolerated at least 2 doses of 1.0 mg/kg in Part B. Participants who received and tolerated at least 4 doses of SBC-103 QOW at 3.0 mg/kg were considered for participation in Part C.

Part C: Participants received SBC-103 5.0 or 10.0 mg/kg administered IV QOW. Dosing in Part C began at the 5.0 mg/kg dose level. The decision to begin dosing the first participant at 10.0 mg/kg was based on the review of safety data at 5.0 mg/kg.

TEAEs were defined as any adverse event (AE) that occurred after administration of the first dose of study drug on Day 1 (Part A). A severe AE was defined as an AE that was incapacitating and required medical intervention. TEAEs were summarized cumulatively over the entire study and separately for Part C, data for all severe TEAEs throughout the entire study is presented. A summary of serious and all other non-serious AEs regardless of causality is located in the Reported Adverse Events module.

Part A (Initial therapy): Participants received SBC-103, 0.3, 1.0, or 3.0 mg/kg QOW for 24 weeks, followed by a ≥ 4-week treatment break. Participants enrolled in the lowest dosage first.

Part B: Participants were escalated to the next highest dose that was considered safe (1.0 or 3.0 mg/kg QOW) for ≥ 8 weeks. Participants who received doses of 0.3 mg/kg in Part A were considered for a second dose escalation to 3.0 mg/kg at any time during Part B provided that they tolerated at least 2 doses of 1.0 mg/kg in Part B. Participants who received and tolerated at least 4 doses of SBC-103 QOW at 3.0 mg/kg were considered for participation in Part C.

Part C: Participants received SBC-103 5.0 or 10.0 mg/kg administered IV QOW. Dosing in Part C began at the 5.0 mg/kg dose level. The decision to begin dosing the first participant at 10.0 mg/kg was based on the review of safety data at 5.0 mg/kg.

TEAEs were defined as any adverse event (AE) that occurred after administration of the first dose of study drug on Day 1 (Part A). A severe AE was defined as an AE that was incapacitating and required medical intervention. TEAEs were summarized cumulatively over the entire study and separately for Part C, data for all severe TEAEs throughout the entire study is presented. A summary of serious and all other non-serious AEs regardless of causality is located in the Reported Adverse Events module.

Safety Population: all participants for whom informed consent had been obtained, who had a confirmed diagnosis of MPS IIIB, and who had received any amount of SBC-103.

Part A (Initial therapy): Participants received SBC-103, 0.3, 1.0, or 3.0 mg/kg QOW for 24 weeks, followed by a ≥ 4-week treatment break. Participants enrolled in the lowest dosage first.

Part B: Participants were escalated to the next highest dose that was considered safe (1.0 or 3.0 mg/kg QOW) for ≥ 8 weeks. Participants who received doses of 0.3 mg/kg in Part A were considered for a second dose escalation to 3.0 mg/kg at any time during Part B provided that they tolerated at least 2 doses of 1.0 mg/kg in Part B. Participants who received and tolerated at least 4 doses of SBC-103 QOW at 3.0 mg/kg were considered for participation in Part C.

Part C: Participants received SBC-103 5.0 or 10.0 mg/kg administered IV QOW. Dosing in Part C began at the 5.0 mg/kg dose level. The decision to begin dosing the first participant at 10.0 mg/kg was based on the review of safety data at 5.0 mg/kg.