This clinical trial is focused on studying a condition called Phenylketonuria (PKU), which is a type of metabolic disorder. People with PKU have difficulty breaking down an amino acid called phenylalanine, which is found in many foods. The study is testing a treatment called PTC923, also known as Sepiapterin, which is taken as a powder by mouth. The purpose of the study is to evaluate the long-term safety of this treatment and to observe any changes in the participants’ diet, specifically their intake of phenylalanine and protein.

Participants in the study will take PTC923 for a period of up to 24 months. During this time, researchers will monitor the safety of the treatment by checking for any side effects and conducting regular health assessments, including laboratory tests and physical exams. The study will also look at how the treatment affects the participants’ quality of life and their ability to tolerate dietary phenylalanine. Some participants will be asked to complete questionnaires about their quality of life, depending on their age and language.

The study aims to provide valuable information about the safety and effectiveness of PTC923 in managing Phenylketonuria. By understanding how this treatment works over a longer period, researchers hope to improve the care and dietary management of individuals with PKU. The trial is open-label, meaning that both the participants and the researchers know which treatment is being administered. This approach helps in closely monitoring the effects of the treatment throughout the study.