A Study of MZE782 in Adults With PKU

Key Inclusion Criteria: * Males and females 18 to 75 years old * Confirmed diagnosis of PKU * Willing and able to keep diet and protein intake consistent during the study * For some study groups, is willing and able to stop certain PKU medications before starting study treatment * For some study groups, may need to meet additional blood phenylalanine level or background-treatment requirements * Meets minimum blood phenylalanine level requirements for study group Key Exclusion Criteria: * Is pregnant, breastfeeding, or planning to become pregnant or conceive a child during the study * Medical conditions or abnormal test results that could make participation unsafe or make it difficult to complete study procedures or interpret study results * Has recently received another investigational drug * Is unable to swallow tablets or tolerate oral medication Other inclusion/exclusion criteria defined in protocol apply.