From dietary restriction to disease-targeted therapy: Sephience TM (sepiapterin) in phenylketonuria

Phenylketonuria (PKU) is a rare metabolic disorder caused by deficient phenylalanine hydroxylase, leading to toxic phenylalanine buildup and severe neurodevelopmental consequences if untreated. Despite advances in newborn screening and dietary management, treatment options remain limited and burdensome. The recent FDA approval of Sephience (sepiapterin) marks a major advancement in PKU care. Sepiapterin, a precursor of tetrahydrobiopterin (BH₄), enhances enzyme activity and stability, offering therapeutic benefit even in patients unresponsive to BH₄ alone. Results from the pivotal APHENITY Phase III trial demonstrated a substantial 63% mean reduction in blood phenylalanine and significant dietary liberalization, with 97% of participants able to increase natural protein intake safely. Importantly, 43% of prior non-responders to sapropterin showed clinical improvement, highlighting its potential to address key gaps in PKU management. With broad approval for children and adults, Sephience provides a disease-targeted therapy that extends beyond dietary restriction. While careful monitoring for adverse effects such as gastrointestinal symptoms and hypophenylalaninemia is required, this approval represents a transformative step in precision medicine. Sephience has the potential to redefine the standard of care and improve long-term quality of life for individuals living with PKU.