This study is a Phase 3, randomized, double-blind, placebo-controlled study of DTX301 in patients with late-onset OTC deficiency 12 years of age and older.~Participants will be randomized 1:1 to DTX301 or placebo group and followed closely for 64 weeks. At week 64 eligible patients will crossover and receive DTX301 if they had previously received placebo or placebo if they had previously received DTX301.~The planned study duration is up to 324 weeks. Upon completion of this study or early withdrawal, all participants who received DTX301 are invited to enroll in the Disease Monitoring Program (DMP) for follow-up for up to an additional 5 years.
The primary objective is to evaluate the efficacy of DTX301 on the improvement of ornithine transcarbamylase (OTC) function by maintaining safe plasma ammonia levels with removal of dietary protein restriction and alternative pathway medication.