This clinical trial is focused on studying a condition called Phenylketonuria (PKU), which is a rare genetic disorder that affects how the body processes a substance called phenylalanine, found in many foods. The study will compare two treatments: Sepiapterin and Sapropterin. Sepiapterin is a new treatment being tested, while Sapropterin is an existing medication used to help manage PKU. The purpose of the study is to see how effective Sepiapterin is compared to Sapropterin in reducing the levels of phenylalanine in the blood of people with PKU.

Participants in the study will be randomly assigned to receive either Sepiapterin or Sapropterin for a certain period, and then they will switch to the other treatment. This type of study is called a crossover study. The study will last for several weeks, during which participants will take the medication in the form of either soluble tablets or powder for oral use. The researchers will monitor the participants’ blood phenylalanine levels to see how well each treatment works. Some participants may also receive a placebo during the study.

The study aims to provide valuable information about the effectiveness of Sepiapterin compared to Sapropterin in managing PKU. By participating, individuals with PKU can contribute to research that may improve treatment options for this condition in the future. The study is open to both male and female participants who are at least two years old and have been diagnosed with PKU. Participants will need to continue their current diet and follow the study procedures as instructed by the research team.