A Study to Investigate Efficacy and Safety of Pegtibatinase Compared With Placebo in Participants ≥12 to ≤65 Years of Age With Classical Homocystinuria (HCU) Due to Cystathionine Beta Synthase Deficiency Receiving Standard of Care Treatment

The purpose of this study is to measure efficacy and safety of pegtibatinase treatment compared with placebo in participants with classical HCU receiving standard of care. Study details include: * Total Study duration: up to 38 weeks * Screening: * Initial Screening duration: up to 4 weeks * Pre-treatment Diet Standardization Period duration: up to 6 weeks * Blinded Treatment Duration: 24 weeks * 2-week blinded dose titration period * 22-week blinded assessment period * Safety Follow-Up: 4 weeks after last dose (as applicable for those not enrolling in the long term extension study, ENSEMBLE)

Inclusion Criteria: * Must be ≥12 to ≤65 years of age, at the time of signing the informed consent * Must have a diagnosis of classical HCU based on clinical, biochemical, and/or molecular genetic testing * Plasma tHcy ≥80 µM at Screening visit, with allowance for up to 18 participants who may be enrolled with a Screening plasma tHcy ≥50 to \