This study is being conducted to evaluate the effectiveness and safety of a medication called pegtibatinase in individuals living with Classical Homocystinuria. This condition is caused by a deficiency in the cystathionine beta synthase enzyme, which leads to high levels of certain substances in the blood. Participants in the study will continue to receive their usual standard of care treatments while also receiving either pegtibatinase or a placebo via subcutaneous injection, which is a method of delivering medicine through a needle just under the skin.

The goal of the study is to see how pegtibatinase affects levels of total homocysteine (tHcy) and methionine (Met) in the blood. High levels of these substances are common in people with this disease. During the study, blood samples will be taken to monitor these levels and to ensure that the treatment is being tolerated well by the body.