After positive Phase 3 results and longer-term follow-up, sepiapterin was approved by Health Canada on October 7, 2025 under the brand name Sephience.
What Is Sepiapterin?
Sepiapterin is an oral therapy designed to increase levels of tetrahydrobiopterin, commonly called BH4, within the body.
BH4 is an important cofactor for phenylalanine hydroxylase, the enzyme used to convert phenylalanine into tyrosine. In PKU, activity of this enzyme is reduced because of changes in the PAH gene.
By increasing available BH4, sepiapterin is intended to enhance remaining PAH enzyme activity and improve the body's ability to metabolize phenylalanine.
The study included children and adults and used an initial treatment period to identify participants who responded to sepiapterin before moving into a randomized, double-blind comparison with placebo.
The Phase 3 results showed significant reductions in blood phenylalanine among participants who responded to treatment.
Why Was APHENITY Important?
APHENITY helped establish whether sepiapterin could provide clinically meaningful phenylalanine reduction across a broad range of people with PKU.
The results, published in The Lancet in 2024, became an important part of the evidence supporting regulatory review of sepiapterin.
That is no longer the full story.
Health Canada approved sepiapterin on October 7, 2025 under the brand name Sephience.
The completion of Phase 3 research and subsequent regulatory approval mark an important transition: APHENITY is now part of the history explaining how a research therapy became an approved PKU treatment in Canada.
Participants have continued to be followed through the APHENITY Extension Study, which has examined longer-term treatment and changes in dietary phenylalanine tolerance.
Interim results published in 2026 included 169 participants who had received sepiapterin. Among participants who underwent a structured dietary phenylalanine tolerance assessment, average dietary phenylalanine intake increased substantially over 26 weeks while blood phenylalanine continued to be monitored.
These findings suggest that, for some people who respond to sepiapterin, treatment may provide an opportunity not only to lower blood phenylalanine but also to increase the amount of natural protein or phenylalanine tolerated in the diet.
Why Dietary Tolerance Matters
For many people with PKU, treatment burden is not defined only by a blood phenylalanine number.
The amount of natural protein that can safely be included in the diet can affect food choice, meal planning, reliance on specialized medical foods and day-to-day quality of life.
This is why the extension research examining dietary phenylalanine tolerance is an important addition to the original Phase 3 results. It begins to answer not simply whether the medicine changes a laboratory value, but what that change may mean in everyday life.
Families and individuals who participated in APHENITY and its related studies helped researchers determine whether the treatment worked, how well it was tolerated and how treatment could affect dietary phenylalanine tolerance over time.
Those findings ultimately contributed to a new approved treatment option for PKU in Canada.
Whether Sephience is appropriate for an individual person with PKU depends on factors including age, treatment response, metabolic goals and clinical circumstances, and should be discussed with the metabolic care team.
With the Phase 3 study complete and sepiapterin now approved in Canada, the value of this information has changed. Rather than maintain an outdated study listing, we are preserving the research story here and directing readers to current regulatory, treatment and research sources for information that continues to evolve.
Learn More
Explore the original Phase 3 research and longer-term follow-up.
View the APHENITY Phase 3 Study ClinicalTrials.gov NCT05099640 Read the Published APHENITY Results The Lancet, 2024 View the APHENITY Extension Study Read the 2026 Dietary Tolerance Results Genetics in Medicine, 2026About this article: CanPKU+ provides plain-language research information to help our community understand how research contributes to new treatment options and changes in PKU care.
