A Phase 3 Long-term Extension Study to Assess the Long-term Safety and Efficacy of Pegtibatinase Treatment in Participants ≥5 to ≤65 Years of Age With Classical Homocystinuria (HCU) (ENSEMBLE)

The goal of this long-term extension (LTE) study is to evaluate the safety and efficacy of pegtibatinase in patients with classical homocystinuria (HCU). Patients who are active in the Phase 1/2 COMPOSE study or those who complete the 24 weeks of treatment in the Phase 3 HARMONY are eligible to participate. Participants will be in this clinical study for up to about 13 months including: * a treatment period of up to 104 weeks * a 4-week safety follow-up period

Overall Design: This is a global, multicenter, single-arm, open-label study. Participants who meet all eligibility criteria may transition from other pegtibatinase studies and enroll into this LTE study for long-term safety, efficacy, and clinical assessments of pegtibatinase treatment. All participants will follow a protocol of self-administration of pegtibatinase unless exempted. During the ENSEMBLE study, an optional protein tolerance modification (PTM) sub-study will also be conducted for eligible participants.